diagram - Documentation toolbox

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# diagram(n) 0.3 tklib "Documentation toolbox"

## Name

diagram - Diagram drawing

## Table Of Contents

## Synopsis

- package require Tcl 8.5
- package require Tk 8.5
- package require diagram 1

- ::diagram objectName canvas ?script?
- diagramObject new direction name ?key value...?
- diagramObject new element name attributes cmdprefix
- diagramObject new alias name cmdprefix
- diagramObject new command name arguments body
- diagramObject new attribute name ?key value...?
- diagramObject unknown attribute cmdprefix
- diagramObject draw script
- arc attr...
- arrow attr...
- --> attr...
- <--> attr...
- <--> attr...
- block script attr...
- box attr...
- circle attr...
- O attr...
- diamond attr...
- <> attr...
- drum attr...
- ellipse attr...
- line attr...
- -- attr...
- move attr
- spline attr...
- text attr...
- west
- w
- left
- l
- south
- s
- down
- bottom
- bot
- b
- east
- e
- right
- r
- north
- n
- up
- top
- t
- northwest
- nw
- up-left
- upleft
- leftup
- northeast
- ne
- up-right
- upright
- rightup
- southwest
- sw
- down-left
- downleft
- leftdown
- southeast
- se
- down-right
- downright
- rightdown
- number cm
- number mm
- number inch
- number pt
- number number
- by distance direction
- point1 + point2
- point1 - point2
- point by distance direction
- point1 | point2
- n between poin1 point2
- intersect elem1 elem2
- element names ?pattern?
- element corner
- element corner1 corner2...
- element ?corner1... ?names ?pattern??]?
- nth ?corner?
- nth last ?corner?
- nth shape ?corner?
- nth last shape ?corner?
- last ?corner?
- last shape ?corner?
- 1st
- 2nd
- 3rd

## Description

Welcome to diagram, a package for the easy construction of diagrams (sic), i.e. 2D vector graphics, sometimes also called pictures. Note that this package is not a replacement for Tk's canvas, but rather a layer sitting on top of it, to make it easier to use. In other words, using the canvas as the core graphics engine diagram abstracts away from the minutiae of handling coordinates to position and size the drawn elements, allowing the user to concentrate on the content of the diagram instead.

This is similar to Brian Kernighan's PIC language for troff, which is the spiritual ancestor of this package.

This document contains the reference to the API and drawing (language) commands. Its intended audience are users of the package wishing to refresh their memory. Newcomers should read the Diagram Language Tutorial first. Developers wishing to work on the internals of the package and its supporting packages should look at section Diagram Classes first, and then the comments in the sources of the packages itself.

In the remainder of the document we first describe the APIs of the diagram class and its instances, followed by the language reference for the drawing language itself.

## API

### Class API

The package exports the API described here.

::diagram objectName canvas ?script?

  The command creates a new instance of a diagram controller and returns the fully qualified name of the object command as its result. The new instance is connected to the specified canvas object, which is used as the diagrams graphics engine. This is usually an instance of Tk's canvas, however any object which is API compatible to Tk's canvas can be used here.

  The API of this object command is described in the following section, Object API. It may be used to invoke various operations on the object.

  If the script argument is specified then method draw will be invoked on it.

### Object API

Instances of the diagram class support the following methods:

diagramObject new direction name ?key value...?

  This method defines a new named direction and its attributes. The latter is given through the key/value pairs coming after the name.

  Users are mostly free to specify arbitrary attributes with whatever meaning they desire. The exception are the names angle and opposite. They are special to the diagram package and have a fixed meaning.

  angle

    This attribute specifies the angle of the direction in degrees, where 0 points east (to the right) and 90 points north (up).

  opposite

    This attribute specifies the name of the direction which should be considered as complementary to the named one.

diagramObject new element name attributes cmdprefix

  This method defines a new graphics element for the drawing language. I.e. name will become a new command in the language, and the specified command prefix (cmdprefix) will be called to perform the actual drawing.

  attributes specifies the set of attributes for which data has to be available. I.e. the system will run the ...-callbacks for these attributes. See the method new attribute for more information on attribute definitions.

  The command prefix is expected to conform to the following signature:

  cmdprefix canvas attributes

    Where canvas is the handle of the canvas widget to draw to, and attributes is a dictionary holding the attributes for the element, be they user-specified, or defaults.

    The results of the command has to be a list containing at least two and at most four items. These are, in order:

    1. The list of canvas items the drawn element consists of.

    2. The dictionary of named locations in the element, its corners.

    3. An optional mode, either "relative" or "absolute". When not returned "relative" is assumed. In the case of a relative element position the attributes "with" and "at" are used to determine the final position of the new element.

    4. An optional name of a direction. If not the empty string this is handed to the automatic layouter as the new direction to follow.

diagramObject new alias name cmdprefix

  This method defines a new command for the drawing language. I.e. name will become a new command in the language, and the specified command prefix (cmdprefix) will be called on use of this new command. Any arguments given to the command are simply passed to the prefix. There is no fixed siganture.

  Note that the prefix is run in the context of the drawing language, allowing the direct use of any existing commands.

diagramObject new command name arguments body

  This is like new alias except that the new command is defined as a procedure in the language's context, with regular argument list and body.

diagramObject new attribute name ?key value...?

  This method defines a new named attribute which can be used by graphical elements. The handling of the attribute by the processor is declared through the key/value pairs coming after the name.

  The accepted keys and their meanings are:

  key

    The value of this key is the name of the key under which the attribute's value shall be stored in the attribute dictionary given to the drawing command after attribute processing is complete.

    This key is optional. If it is not specified it defaults to the name of the attribute.

  get

    The value of this key is a command prefix which will be invoked to retrieve the attribute's argument(s) from the command line.

    This key is optional. If it is not specified a default is used which takes the single word after the attribute name as the attribute's value.

    The signature of the command prefix is

    cmdprefix wordqueue

      Where wordqueue is the handle of a queue object conforming to the API of the queues provided by package struct::queue. This queue contains the not-yet-processed part of the attribute definitions, with one entry per word, with the first entry the word after name of the attribute. In other words, the attribute's name has already been removed from the queue.

      The result of the command is the value of the attribute, which may have been taken from the queue, or not.

  transform

    The value of this key is a command prefix which will be invoked to transform the retrieved value (See get) into their final form.

    This key is optional. If it is not specified no transformation is done. The signature of the command prefix is

    cmdprefix value

      Where value is the value to transform.

      The result of the command is the final value of the attribute.

  type

    The value of this key is a command prefix which will be invoked to validate the attribute's argument(s).

    This key is optional. If it is not specified no validation is done.

    The signature of the command prefix is that of snit validation types. See the documentation of the snit package.

  merge

    The value of this key is a command prefix which will be invoked to insert the transformed and validated attribute value into the dictionary of collected attributes.

    This key is optional. If it is not specified a default merge is chosen, based on the data for key aggregate, see below. The signature of the command prefix is

    cmdprefix value dict

      Where value is the value to insert, and dict the dictionary of attributes and values collected so far.

      The result of the command is the new dictionary of attributes.

  aggregate

    The value of this key is a boolean flag. It has an effect if and only if the key merge was not specified. This key is optional. If it is not specified it defaults to False.

    If the key is effective, the value of False means that the attribute's value is set into the dictionary using the value of key key (see above) as index, overwriting any previously specified value.

    If the key is effective, the value of True means that the attribute's value is added to the dictionary using the value of key key (see above) as index, extending any previously specified value. This means that the final value of the attribute as seen after processing will be a list of the collected values.

  default

    The value of this key is a command prefix which will be invoked after collection of attributes has been completed and this attribute is in the list of required attributes for the drawing element (See argument attributes of method new element).

    Note that the connection is made through the value of key key, not through the attribute name per se.

    Further note that this command prefix is invoked even if a user specified attribute value is present. This allows the command to go beyond simply setting defaults, it can calculate and store derived values as well.

    This key is optional. If an element requires this attribute, but default is not specified then nothing will be done.

    The signature of the command prefix is

    cmdprefix init

      This method is run when the attribute is defined, its responsibility is to initialize anything in the language namespace for the attribute and default processing.

      The result of this method is ignored.

    cmdprefix fill varname

      This method is run to put defaults, or derived values into the attribute dictionary named by varname. This variable will be found in the calling context.

      The result of this method is ignored.

    cmdprefix set name value

      This method is run to push current a attribute value into the language namespace, to make it the new default.

      The result of this method is ignored.

  linked

    This key is effective if and only if key default is not specified. In that case is supplies a default handling for default, linking the attribute to a variable in the language context.

    The value for this key is a 2-element list containing the name of the variable to link to, and its initial value, in this order.

diagramObject unknown attribute cmdprefix

  This method registers the command prefix with the subsystem processing the attributes for element commands, telling it to call it when it encounters an attribute it is unable to handle on its on.

  It is allowed to register more than callback, these will be called in order of registration (i.e. first to last), until one of the callbacks accepts the current input. The command prefix is expected to conform to the following signature:

  cmdprefix wordqueue

    Where wordqueue is the handle of a queue object conforming to the API of the queues provided by package struct::queue. This queue contains the not-yet-processed part of the attribute definitions, with one entry per word, with the first entry the name of the attribute which could not be processed.

    The results of the command has to be a boolean value where True signals that this callback has accepted the attribute, processed it, and the new state of the wordqueue is where the general processing shall continue.

    Given the signature the command has basically two ways of handling (rewriting) the attributes it recognizes:

    1. Replace the attribute (and arguments) with a different attribute and arguments.

    2. Push additional words in front to get the general processing unstuck.

diagramObject draw script

  This method runs the given script in the context of the drawing language definitions. See section Language Reference for details on the available commands.

  Note that script is trusted. It is executed in the current interpreter with access to its full abilities. For the execution of untrusted diagram scripts this interpreter should be a safe one.

## Language Reference

### Elements

This section lists the commands for the predefined drawing elements, aka shapes. These commands are all defined in the language's context. All commands of this section return the handle of the newly created element as their result. This handle also exists as a command which can be used to query the element for its corners (names, values). See section Miscellaneous Commands.

arc attr...

  An open element with the corresponding corners, i.e. "start", "end", and "center". Note however that it also has the compass rose of closed elements as its corners, with the center of the arc's circle as the center of the compass and the other points on the circle the arc is part of. It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  clockwise
  cw

    Specifies the direction of the arc element, here going clockwise. The complementary attribute is counterclockwise. If not specified the system falls back to the value taken from the language variable clockwise, which itself defaults to false, for counter-clockwise direction.

  color spec

    Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

  counterclockwise
  ccw

    Specifies the direction of the arc element, here counter-clockwise. The complementary attribute is clockwise. If not specified the system falls back to the value taken from the language variable clockwise, which itself defaults to false, for counter-clockwise direction.

  fillcolor spec

    Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

  from location

    Specifies the location where the arc element begins. Defaults to the current location as maintained by the layouting system.

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  radius length

    Specifies the radius of the arc element, or rather, the radius of the circle the shown arc is a part of. If not specified the system falls back to the value taken from the language variable arcradius, which itself defaults to the pixel equivalent of 1 cm.

  stroke width

    Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

  style spec

    Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

    solid, empty string

      Draw solid line.

    dash, dashed, -

      Draw a dashed line.

    dot, dotted, .

      Draw a dotted line.

    dash-dot, -.

      Draw a dash-dotted line

    dash-dot-dot, -..

      Draw a dash-dot-dotted line.

    Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  to location

    Specifies the location where the arc element ends. Defaults to a location such that a 90-degree arc is drawn in the chosen direction, starting at from.

arrow attr...
--> attr...
<--> attr...
<--> attr...

  An alias for the line element (see below), with the attribute arrowhead preset to ->, <->, or <-. The arrow is equivalent to -->.

block script attr...

  A closed element with the corresponding corners, i.e. the eight directions of the compass rose, and "center". The main effect is the aggregration of all elements created by the script into one element. This also means that while the elements created by the script are visible in the element history while the script is executing, afterward the history contains only the block itself, and not the elements it is composed of.

  The script has access to the current state of all variables in the language context. Any changes to the variables will be reverted after execution of the block. However, also, any variables set in the script will be exported as corners of the element, allowing users to define their own named locations in the block.

  Regarding the layout mechanism any changes made by the script are reverted after the element is done. In other words, a block is an implicit group.

  Blocks handle all attributes, propgating their settings into the script as the default values active during script execution.

box attr...

  A closed element with the corresponding corners, i.e. the eight directions of the compass rose, and "center". It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  at location

    Specifies the location of the element's corner named by the attribute with. Defaults to the current location as maintained by the layouting system.

  color spec

    Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

  fillcolor spec

    Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

  height length
  ht length

    Specifies the height of the element. If not specified the system falls back to the value taken from the language variable boxheight, which itself defaults to the pixel equivalent of 2 cm.

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  slant angle

    Specifies the angle by which the box element is slanted, in degrees. If not specified the system falls back to the value taken from the language variable slant, which itself defaults to 90, i.e. vertical, no slant. 0 degrees is slanting straight east, pointing to the right. 90 degrees is slanting to the north, pointing straight up.

  stroke width

    Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

  style spec

    Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

    solid, empty string

      Draw solid line.

    dash, dashed, -

      Draw a dashed line.

    dot, dotted, .

      Draw a dotted line.

    dash-dot, -.

      Draw a dash-dotted line

    dash-dot-dot, -..

      Draw a dash-dot-dotted line.

    Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  width length
  wid length

    Specifies the width of the element. If not specified the system falls back to the value taken from the language variable boxwidth, which itself defaults to the pixel equivalent of 2 cm.

  with corner

    Specifies the corner of the element to place at the location given by the attribute at. Defaults to the current corner as maintained by the layouting system, except if the value for at was specified by the user. In that case it defaults to center.

circle attr...
O attr...

  A closed element with the corresponding corners, i.e. the eight directions of the compass rose, and "center". It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  at location

    Specifies the location of the element's corner named by the attribute with. Defaults to the current location as maintained by the layouting system.

  color spec

    Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

  diameter length
  diam length

    Specifies the diameter of the circle element, as an alternative way to specify its radius. Effective if and only if the radius was not specified. I.e. if both diameter and radius are specified then the radius infomration has precendence. This attribute has no default, because the defaults are taken from the radius.

  fillcolor spec

    Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  radius length
  rad length

    Specifies the radius of the circle element. If not specified the system falls back to the value taken from the language variable circleradius, which itself defaults to the pixel equivalent of 1 cm.

  stroke width

    Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

  style spec

    Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

    solid, empty string

      Draw solid line.

    dash, dashed, -

      Draw a dashed line.

    dot, dotted, .

      Draw a dotted line.

    dash-dot, -.

      Draw a dash-dotted line

    dash-dot-dot, -..

      Draw a dash-dot-dotted line.

    Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  with corner

    Specifies the corner of the element to place at the location given by the attribute at. Defaults to the current corner as maintained by the layouting system, except if the value for at was specified by the user. In that case it defaults to center.

diamond attr...
<> attr...

  A closed element with the corresponding corners, i.e. the eight directions of the compass rose, and "center". It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  aspect number

    Specifies the aspect ratio, i.e ratio of width to height, of the diamond element. The manner in which a default is calculated when not specified also depends on the specifications of the attributes width and height, if any.

    If both width, and height are specified then any specification of aspect is ignored, as it is implicitly defined in the width and height as well, and this takes precedence. A missing specification is ignored in that case well, i.e. no defaults are required.

    If the aspect is specified, and one of the attributes width or height, then the missing attribute is calculated from the two which are specified. No defaults are required for these cases either.

    If only one of the attributes width or height is specified then the system uses a fallback for the aspect, the value taken from the language variable diamondaspect, which itselfs defaults to 2.

    If none of of the attributes width or height is specified then the system uses a fallback for the width, the value taken from the language variable boxwidth, which itselfs defaults to the pixel equivalent of 2 cm. For the aspect it uses either the user-specified value or the default taken as described in the previous paragraph.

  at location

    Specifies the location of the element's corner named by the attribute with. Defaults to the current location as maintained by the layouting system.

  color spec

    Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

  fillcolor spec

    Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

  height length

    Specifies the height of the diamond element. The manner in which a default is calculated when not specified also depends on the specifications of the attributes aspect and width, if any.

    If both width, and height are specified then any specification of aspect is ignored, as it is implicitly defined in the width and height as well, and this takes precedence. A missing specification is ignored in that case well, i.e. no defaults are required.

    If the aspect is specified, and one of the attributes width or height, then the missing attribute is calculated from the two which are specified. No defaults are required for these cases either.

    If only one of the attributes width or height is specified then the system uses a fallback for the aspect, the value taken from the language variable diamondaspect, which itselfs defaults to 2.

    If none of of the attributes width or height is specified then the system uses a fallback for the width, the value taken from the language variable boxwidth, which itselfs defaults to the pixel equivalent of 2 cm. For the aspect it uses either the user-specified value or the default taken as described in the previous paragraph.

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  stroke width

    Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

  style spec

    Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

    solid, empty string

      Draw solid line.

    dash, dashed, -

      Draw a dashed line.

    dot, dotted, .

      Draw a dotted line.

    dash-dot, -.

      Draw a dash-dotted line

    dash-dot-dot, -..

      Draw a dash-dot-dotted line.

    Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  width length

    Specifies the width of the diamond element. The manner in which a default is calculated when not specified also depends on the specifications of the attributes aspect and height, if any.

    If both width, and height are specified then any specification of aspect is ignored, as it is implicitly defined in the width and height as well, and this takes precedence. A missing specification is ignored in that case well, i.e. no defaults are required.

    If the aspect is specified, and one of the attributes width or height, then the missing attribute is calculated from the two which are specified. No defaults are required for these cases either.

    If only one of the attributes width or height is specified then the system uses a fallback for the aspect, the value taken from the language variable diamondaspect, which itselfs defaults to 2.

    If none of of the attributes width or height is specified then the system uses a fallback for the width, the value taken from the language variable boxwidth, which itselfs defaults to the pixel equivalent of 2 cm. For the aspect it uses either the user-specified value or the default taken as described in the previous paragraph.

  with corner

    Specifies the corner of the element to place at the location given by the attribute at. Defaults to the current corner as maintained by the layouting system, except if the value for at was specified by the user. In that case it defaults to center.

drum attr...

  A closed element with the corresponding corners, i.e. the eight directions of the compass rose, and "center". It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  aspect number

    Specifies the aspect ratio, i.e ratio of width to height, of the ellipses which are used to draw the top and bottom of the drum element. If not specified the system falls back to the value taken from the language variable drumaspect, which itself defaults to 0.35.

  at location

    Specifies the location of the element's corner named by the attribute with. Defaults to the current location as maintained by the layouting system.

  color spec

    Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

  fillcolor spec

    Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

  height length
  ht length

    Specifies the height of the element. If not specified the system falls back to the value taken from the language variable boxheight, which itself defaults to the pixel equivalent of 2 cm.

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  stroke width

    Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

  style spec

    Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

    solid, empty string

      Draw solid line.

    dash, dashed, -

      Draw a dashed line.

    dot, dotted, .

      Draw a dotted line.

    dash-dot, -.

      Draw a dash-dotted line

    dash-dot-dot, -..

      Draw a dash-dot-dotted line.

    Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  width length
  wid length

    Specifies the width of the element. If not specified the system falls back to the value taken from the language variable boxwidth, which itself defaults to the pixel equivalent of 2 cm.

  with corner

    Specifies the corner of the element to place at the location given by the attribute at. Defaults to the current corner as maintained by the layouting system, except if the value for at was specified by the user. In that case it defaults to center.

ellipse attr...

  A closed element with the corresponding corners, i.e. the eight directions of the compass rose, and "center". It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  at location

    Specifies the location of the element's corner named by the attribute with. Defaults to the current location as maintained by the layouting system.

  color spec

    Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

  fillcolor spec

    Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

  height length
  ht length

    Specifies the height of the element. If not specified the system falls back to the value taken from the language variable boxheight, which itself defaults to the pixel equivalent of 2 cm.

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  stroke width

    Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

  style spec

    Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

    solid, empty string

      Draw solid line.

    dash, dashed, -

      Draw a dashed line.

    dot, dotted, .

      Draw a dotted line.

    dash-dot, -.

      Draw a dash-dotted line

    dash-dot-dot, -..

      Draw a dash-dot-dotted line.

    Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  width length
  wid length

    Specifies the width of the element. If not specified the system falls back to the value taken from the language variable boxwidth, which itself defaults to the pixel equivalent of 2 cm.

  with corner

    Specifies the corner of the element to place at the location given by the attribute at. Defaults to the current corner as maintained by the layouting system, except if the value for at was specified by the user. In that case it defaults to center.

line attr...
-- attr...

  An open element with the corresponding corners, i.e. "start", "end", and "center". It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  arrowhead spec

    Specifies where to draw arrowheads on the line element, at the beginning or end, at both ends, or none. If not specified the system falls back to the value taken from the language variable arrowhead, which itself defaults to none. The legal values are

    none, -

      Draw no arrowheads, at neither end of the line.

    start, first, <-

      Draw an arrowhead at the beginning of the line, but not at its end.

    end, last, ->

      Draw an arrowhead at the end of the line, but not at its beginning.

    both, <->

      Draw arrowheads at both ends of the line.

    Note that the values "start", "end", "-", "->", "<-", and "<->" are all accepted as shorthands for the arrowhead command using them as argument.

  at location

    Line elements are normally positioned absolutely, using the locations specified through the attributes from, then, and to. If at is specified however then these positions are translated a last time, moving the line's corner named by the attribute with to the location given by this attribute.

  chop ?length?

    Specifies the length of the line element to remove from the beginning and/or end. Defaults to nothing. If specified once the chopping applies to both beginning and end of the line. If specified twice or more the last two specifications are used, and applied to beginning and end of the line, in this order. Whenever the attribute is specified without an explicit length, the system falls back to the value taken from the language variable circleradius, which itself defaults to the pixel equivalent of 1 cm

  color spec

    Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

  fillcolor spec

    Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

  from location

    Specifies the location where the line element begins. Defaults to the current location as maintained by the layouting system.

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  noturn

    Specifies that the direction of line element at its end is not propagated to the layout management. If not specified the direction of the line becomes the new direction the layout.

  smooth

    Specifies the use of bezier splines for the line element. If not specified lines are drawn exactly through the specified waypoints, without any smooth curves.

  stroke width

    Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

  style spec

    Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

    solid, empty string

      Draw solid line.

    dash, dashed, -

      Draw a dashed line.

    dot, dotted, .

      Draw a dotted line.

    dash-dot, -.

      Draw a dash-dotted line

    dash-dot-dot, -..

      Draw a dash-dot-dotted line.

    Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  then location
  then (<direction> ?length?)...
  (<direction> ?length?)...

    This attribute specifies an intermediate location the line element has to go through. It can be specified multiple times, with each use adding one additional location to the series which the line will go through. These location will be traversed in the order they were specified.

    The location can be given explicitly, or as a series of directions with distances. In the latter case the names of all known directions are accepted for the direction part. If no distance is specified for a direction the system falls back to the value taken from the language variable movelength, which itself defaults to the pixel equivalent of 2 cm. The whole set of direction,distance pairs is treated as a series of translations which are added up to provide the final translation specifying the intermediate point (relative to the preceding point).

    The last named direction is propagated to the layout system as the direction to follow. The use of noturn is not able to overide this behaviour.

    At last, the names of the registered directions also serve as attribute commands, with an implicit attribute then in front of them.

    If no intermediate or last location is specified for the line the system falls back to a point movelength pixels away from the starting location, in the current direction as maintained by the layouting system

  to location

    Specifies the location where the line element ends. This attribute has no default. The default is handled by the attribute then, which makes it appear as if to has a default when not specified.

  with corner

    Line elements are normally positioned absolutely, using the locations specified through the attributes from, then, and to. If at is specified however then these positions are translated a last time, moving the line's corner named by the attribute with to the location given by this attribute. This means that with is effective if and only if the attribute at was specified as well for the line.

move attr

  An open element with the corresponding corners, i.e. "start", "end", and "center". A move element is in essence an invisible line. While the main effect we are interested in is the change it makes to the layout system, it is an actual element, i.e. it has the same corners as an ordinary line, and shows up in the history as well, allowing future references to all the places it touched. It handles the same attibutes as line elements.

spline attr...

  An alias for the line element (see above), with the attribute smooth preset.

text attr...

  A closed element with the corresponding corners, i.e. the eight directions of the compass rose, and "center". It handles the attributes

  anchor name
  ljust
  rjust
  above
  below

    Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

    ljust

      "anchor west"

    rjust

      "anchor east"

    above

      "anchor south"

    below

      "anchor north"

  at location

    Specifies the location of the element's corner named by the attribute with. Defaults to the current location as maintained by the layouting system.

  height length

    Specifies the height of the text element. Defaults to the natural height of its text.

  justify left|center|right

    Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

  text string

    Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

  textcolor spec

    Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

  textfont spec

    Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

  width length

    Specifies the width of the text element. Defaults to the natural width of its text.

  with corner

    Specifies the corner of the element to place at the location given by the attribute at. Defaults to the current corner as maintained by the layouting system, except if the value for at was specified by the user. In that case it defaults to center.

### Attributes

The set of all attributes supported by all the element commands is shown below. While we speak of them as commands, and provide a syntax, they are not truly available as actual commands, but only as part of the arguments for an element command.

Note that some of the attribute names are overloaded, i.e. have multiple, different, definitions. During processing of attributes for an element the actual definition used is chosen based on the type of the element the processing is for.

Further, as a catch-all clause, any attribute which could not be processed according to the definitions below will be treated as the argument of an implicit text attribute.

anchor name
ljust
rjust
above
below

  Specifies the anchor of the text which is to be placed at the element's center, by name. I.e. this attribute defines the text's position relative to the element's center. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable anchor, which itself defaults to center. The legal values are all those accepted by Tk_GetAnchor. The commands without arguments are all shorthands with the anchor implied. Note that they do not combine, only the last is used. For comined directions the main attribute command, anchor has to be used.

  ljust

    "anchor west"

  rjust

    "anchor east"

  above

    "anchor south"

  below

    "anchor north"

arrowhead spec

  Specifies where to draw arrowheads on the line element, at the beginning or end, at both ends, or none. If not specified the system falls back to the value taken from the language variable arrowhead, which itself defaults to none. The legal values are

  none, -

    Draw no arrowheads, at neither end of the line.

  start, first, <-

    Draw an arrowhead at the beginning of the line, but not at its end.

  end, last, ->

    Draw an arrowhead at the end of the line, but not at its beginning.

  both, <->

    Draw arrowheads at both ends of the line.

  Note that the values "start", "end", "-", "->", "<-", and "<->" are all accepted as shorthands for the arrowhead command using them as argument.

aspect number

  Specifies the aspect ratio, i.e ratio of width to height, of the diamond element. The manner in which a default is calculated when not specified also depends on the specifications of the attributes width and height, if any.

  If both width, and height are specified then any specification of aspect is ignored, as it is implicitly defined in the width and height as well, and this takes precedence. A missing specification is ignored in that case well, i.e. no defaults are required.

  If the aspect is specified, and one of the attributes width or height, then the missing attribute is calculated from the two which are specified. No defaults are required for these cases either.

  If only one of the attributes width or height is specified then the system uses a fallback for the aspect, the value taken from the language variable diamondaspect, which itselfs defaults to 2.

  If none of of the attributes width or height is specified then the system uses a fallback for the width, the value taken from the language variable boxwidth, which itselfs defaults to the pixel equivalent of 2 cm. For the aspect it uses either the user-specified value or the default taken as described in the previous paragraph.

aspect number

  Specifies the aspect ratio, i.e ratio of width to height, of the ellipses which are used to draw the top and bottom of the drum element. If not specified the system falls back to the value taken from the language variable drumaspect, which itself defaults to 0.35.

at location

  Specifies the location of the element's corner named by the attribute with. Defaults to the current location as maintained by the layouting system.

at location

  Line elements are normally positioned absolutely, using the locations specified through the attributes from, then, and to. If at is specified however then these positions are translated a last time, moving the line's corner named by the attribute with to the location given by this attribute.

chop ?length?

  Specifies the length of the line element to remove from the beginning and/or end. Defaults to nothing. If specified once the chopping applies to both beginning and end of the line. If specified twice or more the last two specifications are used, and applied to beginning and end of the line, in this order. Whenever the attribute is specified without an explicit length, the system falls back to the value taken from the language variable circleradius, which itself defaults to the pixel equivalent of 1 cm

clockwise
cw

  Specifies the direction of the arc element, here going clockwise. The complementary attribute is counterclockwise. If not specified the system falls back to the value taken from the language variable clockwise, which itself defaults to false, for counter-clockwise direction.

color spec

  Specifies the color used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linecolor, which itself defaults to black.

counterclockwise
ccw

  Specifies the direction of the arc element, here counter-clockwise. The complementary attribute is clockwise. If not specified the system falls back to the value taken from the language variable clockwise, which itself defaults to false, for counter-clockwise direction.

diameter length
diam length

  Specifies the diameter of the circle element, as an alternative way to specify its radius. Effective if and only if the radius was not specified. I.e. if both diameter and radius are specified then the radius infomration has precendence. This attribute has no default, because the defaults are taken from the radius.

fillcolor spec

  Specifies the color used to draw the inside of the element. If not specified the system falls back to the value taken from the language variable fillcolor, which itself defaults to the empty string, signaling "no filling".

from location

  Specifies the location where the line element begins. Defaults to the current location as maintained by the layouting system.

from location

  Specifies the location where the arc element begins. Defaults to the current location as maintained by the layouting system.

height length
ht length

  Specifies the height of the element. If not specified the system falls back to the value taken from the language variable boxheight, which itself defaults to the pixel equivalent of 2 cm.

height length

  Specifies the height of the diamond element. The manner in which a default is calculated when not specified also depends on the specifications of the attributes aspect and width, if any.

  If both width, and height are specified then any specification of aspect is ignored, as it is implicitly defined in the width and height as well, and this takes precedence. A missing specification is ignored in that case well, i.e. no defaults are required.

  If the aspect is specified, and one of the attributes width or height, then the missing attribute is calculated from the two which are specified. No defaults are required for these cases either.

  If only one of the attributes width or height is specified then the system uses a fallback for the aspect, the value taken from the language variable diamondaspect, which itselfs defaults to 2.

  If none of of the attributes width or height is specified then the system uses a fallback for the width, the value taken from the language variable boxwidth, which itselfs defaults to the pixel equivalent of 2 cm. For the aspect it uses either the user-specified value or the default taken as described in the previous paragraph.

height length

  Specifies the height of the text element. Defaults to the natural height of its text.

justify left|center|right

  Specifies how multi-line text associated with the element is positioned within its box. The value is ignored if no text was specified for the element. If not specified the system falls back to the value taken from the language variable justify, which itself defaults to left. The legal values are left, right, and center.

noturn

  Specifies that the direction of line element at its end is not propagated to the layout management. If not specified the direction of the line becomes the new direction the layout.

radius length
rad length

  Specifies the radius of the circle element. If not specified the system falls back to the value taken from the language variable circleradius, which itself defaults to the pixel equivalent of 1 cm.

radius length

  Specifies the radius of the arc element, or rather, the radius of the circle the shown arc is a part of. If not specified the system falls back to the value taken from the language variable arcradius, which itself defaults to the pixel equivalent of 1 cm.

slant angle

  Specifies the angle by which the box element is slanted, in degrees. If not specified the system falls back to the value taken from the language variable slant, which itself defaults to 90, i.e. vertical, no slant. 0 degrees is slanting straight east, pointing to the right. 90 degrees is slanting to the north, pointing straight up.

smooth

  Specifies the use of bezier splines for the line element. If not specified lines are drawn exactly through the specified waypoints, without any smooth curves.

stroke width

  Specifies the width of the lines drawn for the the element, in pixels. If not specified the system falls back to the value taken from the language variable linewidth, which itself defaults to 1.

style spec

  Specifies the style used to draw the lines of the element. If not specified the system falls back to the value taken from the language variable linestyle, which itself defaults to solid lines. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

  solid, empty string

    Draw solid line.

  dash, dashed, -

    Draw a dashed line.

  dot, dotted, .

    Draw a dotted line.

  dash-dot, -.

    Draw a dash-dotted line

  dash-dot-dot, -..

    Draw a dash-dot-dotted line.

  Note that the values "solid", "dot(ted)", "dash(ed)", "dash-dot", and "dash-dot-dot" are all accepted as shorthands for the style command using them as argument.

text string

  Specifies the text to associate with the element. Defaults to nothing. When specified multiple times the actually shown text is the concatenation of the individual strings, vertically stacked, with the first string specified being the topmost element.

textcolor spec

  Specifies the color used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textcolor, which itself defaults to black.

textfont spec

  Specifies the font used to draw the text of an element with. Ignored if there is no text. If not specified the system falls back to the value taken from the language variable textfont, which itself defaults to Helvetica 12pt.

then location
then (<direction> ?length?)...
(<direction> ?length?)...

  This attribute specifies an intermediate location the line element has to go through. It can be specified multiple times, with each use adding one additional location to the series which the line will go through. These location will be traversed in the order they were specified.

  The location can be given explicitly, or as a series of directions with distances. In the latter case the names of all known directions are accepted for the direction part. If no distance is specified for a direction the system falls back to the value taken from the language variable movelength, which itself defaults to the pixel equivalent of 2 cm. The whole set of direction,distance pairs is treated as a series of translations which are added up to provide the final translation specifying the intermediate point (relative to the preceding point).

  The last named direction is propagated to the layout system as the direction to follow. The use of noturn is not able to overide this behaviour.

  At last, the names of the registered directions also serve as attribute commands, with an implicit attribute then in front of them.

  If no intermediate or last location is specified for the line the system falls back to a point movelength pixels away from the starting location, in the current direction as maintained by the layouting system

to location

  Specifies the location where the line element ends. This attribute has no default. The default is handled by the attribute then, which makes it appear as if to has a default when not specified.

to location

  Specifies the location where the arc element ends. Defaults to a location such that a 90-degree arc is drawn in the chosen direction, starting at from.

width length
wid length

  Specifies the width of the element. If not specified the system falls back to the value taken from the language variable boxwidth, which itself defaults to the pixel equivalent of 2 cm.

width length

  Specifies the width of the diamond element. The manner in which a default is calculated when not specified also depends on the specifications of the attributes aspect and height, if any.

  If both width, and height are specified then any specification of aspect is ignored, as it is implicitly defined in the width and height as well, and this takes precedence. A missing specification is ignored in that case well, i.e. no defaults are required.

  If the aspect is specified, and one of the attributes width or height, then the missing attribute is calculated from the two which are specified. No defaults are required for these cases either.

  If only one of the attributes width or height is specified then the system uses a fallback for the aspect, the value taken from the language variable diamondaspect, which itselfs defaults to 2.

  If none of of the attributes width or height is specified then the system uses a fallback for the width, the value taken from the language variable boxwidth, which itselfs defaults to the pixel equivalent of 2 cm. For the aspect it uses either the user-specified value or the default taken as described in the previous paragraph.

width length

  Specifies the width of the text element. Defaults to the natural width of its text.

with corner

  Specifies the corner of the element to place at the location given by the attribute at. Defaults to the current corner as maintained by the layouting system, except if the value for at was specified by the user. In that case it defaults to center.

with corner

  Line elements are normally positioned absolutely, using the locations specified through the attributes from, then, and to. If at is specified however then these positions are translated a last time, moving the line's corner named by the attribute with to the location given by this attribute. This means that with is effective if and only if the attribute at was specified as well for the line.

### Corners

Corners are named values for in elements, usually locations.

- The closed elements define corners for the compass rose, including the "center", and their "width" and "height".

- block elements additionally export all variables which were set during their definition as corners.

- The open elements on the other hand define "start", "end", and "center". The first two map to the locations originally provided through the attributes from and to of the element.

- The center of line and move elements is the location halfway between "start" and "end" corners, this is regardless of any intermediate locations the element may have.

- The line and move elements additionally name all their locations as corners using numbers as names, starting from 1 (equivalent to "start"), in order of traversal.

- The center of arc elements is the center of the circle the arc is part off.

- The arc elements additionally define the compass rose of closed elements as well.

### Named directions

The named directions are commands which tell the layout system in which direction to go when placing the next element without an explicit position specification. They can also be used as arguments to the attribute then, and the command by for relative points, see there for the relevant syntax.

The diagram core defines the directions of the compass rose, plus a number of aliases. See below for the full list.

This overlaps with the pre-defined corners for closed elements. This is used by the layout system, when are going in direction X the name of the opposite direction is the name of the corner at which the new element will be attached to the current position, and if this corner does not exist the nearest actual corner by angle is used.

west
w
left
l
south
s
down
bottom
bot
b
east
e
right
r
north
n
up
top
t
northwest
nw
up-left
upleft
leftup
northeast
ne
up-right
upright
rightup
southwest
sw
down-left
downleft
leftdown
southeast
se
down-right
downright
rightdown

### Miscellaneous Commands

number cm
number mm
number inch
number pt

  These commands allow the specification of distances and coordinates in metric and imperial units, returning the equivalent distance or coordinate in pixels, which is the unit used internally for all calculations.

  The conversion factors are based on the result of tk scaling and are computed once, at the time the package is sourced, future changes of the tk scaling factor have no effect.

number number

  This command takes the x and y coordinates of a location and returns the absolute point for it.

by distance direction

  This command takes a distance and direction (angle in degress, or registered direction name) and returns the relative point for it, i.e. the delta or translation it represents.

  Note also the (dis)similarities to the directional specifications for the attribute then of line and move elements. Where we say here

      by 50 east

  for the attribute we say

      ... then east 50 ...

  or just

      ... then east ...

point1 + point2

  This command interprets two points as vectors and adds them together. If at least one of the points is absolute the result is absolute as well. The result is a relative point if and only if both points are relative.

point1 - point2

  This command interprets two points as vectors and subtracts the second from the first. If at least one of the points is absolute the result is absolute as well. The result is a relative point if and only if both points are relative.

point by distance direction

  This command is a more convenient, or at least shorter, form of

          [$point + [by $distance $direction]]

point1 | point2

  This command calculates the projection of two points, i.e. the result is the point having the x-coordinate of point1 and the y-coordinate of point2.

n between poin1 point2

  This command computes the point which is n*100 percent of the way between point1 and point2, and returns it as its result. This means that for

  n == 0

    The result is point1.

  n == 1

    The result is point2.

  n == 0.5

    The result is half way between the two points.

  etc. Note that it is allowed to use values < 0 and > 1 for n

intersect elem1 elem2

  This command takes two open elements, computes the lines going through their "start"- and "end"-corners, and returns the point where these two lines intersect. The command throws an error if the lines do not intersect, or are coincident.

element names ?pattern?

  This command returns a list containing the names of all corners for the element. If a pattern is specified then only the names matching it (via string match are returned. Otherwise all names are returned (equivalent to a default pattern of *).

element corner

  This command returns the value for the corner of the element. This can be anything, including points and elements.

element corner1 corner2...

  This is a convenience shorthand for

      [[[$elem $corner1] $corner2] ...]

  assuming that the value for

       [$elem $corner1]

  , etc. is again an element.

element ?corner1... ?names ?pattern??]?

  This is a convenience shorthand for

      [[[$elem $corner1] ...] names ?pattern?]

  assuming that the value for

       [$elem $corner1]

  , etc. is again an element.

nth ?corner?

  This command asks the diagram history for the nth element created, searching from the beginning of the history (counting from 1) and returns it as its result. If the corner is specified then the value for this corner is returned instead.

nth last ?corner?

  This command asks the diagram history for the nth element created, searching from the end of the history and returns it as its result. If the corner is specified then the value for this corner is returned instead.

nth shape ?corner?

  This command asks the diagram history for the nth element created, of the given shape, searching from the beginning of the history (counting from 1) and returns it as its result. If the corner is specified then the value for this corner is returned instead.

nth last shape ?corner?

  This command asks the diagram history for the nth element created, of the given shape, searching from the end of the history and returns it as its result. If the corner is specified then the value for this corner is returned instead.

last ?corner?
last shape ?corner?

  Convenience commands mapping to "1st last" and "1st last shape".

1st
2nd
3rd

  Aliases for 1th, 2th, and 3th, for readability, usable whereever nth can ocur.

### Variables

The language context contains a number of predefined variables which hold the default values for various attributes. These variables, their uses, and values are:

anchor

  The default value for the attribute anchor. Initialized to center. The legal values are all those accepted by Tk_GetAnchor.

arcradius

  The default value for the attribute radius of arc elements. Initialized to the pixel equivalent of 1 cm.

arrowhead

  The default value for the attribute arrowhead. Initialized to none. The legal values are

  none, -

    Draw no arrowheads, at neither end of the line.

  start, first, <-

    Draw an arrowhead at the beginning of the line, but not at its end.

  end, last, ->

    Draw an arrowhead at the end of the line, but not at its beginning.

  both, <->

    Draw arrowheads at both ends of the line.

boxheight

  The default value for the attribute height of box, diamond and ellipse elements. Initialized to the pixel equivalent of 2 cm.

boxwidth

  The default value for the attribute width of box, diamond and ellipse elements. Initialized to the pixel equivalent of 2 cm.

clockwise

  The default value for the attributes clockwise and counterclockwise of arc elements. Initialized to False, for counter-clockwise direction.

circleradius

  The default value for the attribute radius of circle elements, and also the default for the attribute chop, when specified without an explicit length. Initialized to the pixel equivalent of 1 cm.

drumaspect

  The default value for the attribute aspect of drum elements. Initialized to 0.35.

fillcolor

  The default value for the attribute fillcolor of all elements which can be filled. Initialized to the empty string, signaling that the element is not filled.

justify

  The default value for the attribute justify. Initialized to left. The legal values are left, right, and center.

linecolor

  The default value for the attribute color of all elements having to draw lines (all but text). Initialized to black.

linestyle

  The default value for the attribute style of all elements having to draw some line. Initialized to solid. The legal values are all those accepted by Tk_GetDash, and additionally all which are listed below:

  solid, empty string

    Draw solid line.

  dash, dashed, -

    Draw a dashed line.

  dot, dotted, .

    Draw a dotted line.

  dash-dot, -.

    Draw a dash-dotted line

  dash-dot-dot, -..

    Draw a dash-dot-dotted line.

linewidth

  The default value for the attribute stroke of all elements having to draw some line. Initialized to 1 (pixels).

movelength

  The default value for the directional specification of intermediate locations by the attribute then of line and move elements. Initialized to the pixel equivalent of 2 cm.

slant

  The default value for the attribute slant of box elements. Initialized to 90 degrees, i.e. slant straight up.

textcolor

  The default value for the attribute textcolor of all elements having to draw some text. Initialized to black.

textfont

  The default value for the attribute textfont of all elements having to draw some text. Initialized to Helvetica 12pt.

## Diagram Classes

The intended audience of this section are developers wishing to work on the internals of the diagram package. Regular users of diagram can skip this section without missing anything.

The main information seen here is the figure below, showing the hierarchy of the classes implementing diagram.

At the bottom, all at the same level are the supporting packages like snit, etc. These can all be found in Tcllib.

Above them is the set of diagram classes implementing the various aspects of the system, i.e.:

diagram

  The main class, that which is seen by the user.

diagram::core

  The core engine, itself distributed over four helper classes.

diagram::basic

  The implementation of the standard shapes, like box, circle, etc., based on the extension features of the core.

diagram::element

  Core support class, the database of created elements. It also keeps the history, i.e. the order in which elements were created.

diagram::attribute

  Core support class, the generic handling of definition and processing of attributes.

diagram::direction

  Core support class, the database of named directions.

diagram::navigation

  Core support class, the state of layout engine, i.e. current position and directin, and operations on it.

diagram::point

  General support class handling various vector operations.

## References

## Keywords

2D geometry, arc, arrow, box, canvas, circle, diagram, diamond, drawing, drum, ellipse, image, interpolation, intersection, line, move, picture, plane geometry, plotting, point, raster image, spline, text, vector

## Category

Documentation tools