Custom Shape Module
===================

The custom shape module allows you to create new shapes for Dia
without	writing any C code.  Instead, you just have to write a simple
XML file describing the shape.  This opens up the job of creating new
shapes for dia to non programmers as well.

The actual shape is described using a subset of the SVG
specification.  The line, polyline, polygon, rect, circle, ellipse,
path and g elements are supported.  Note that the path element only
supports the M,m,L,l,H,h,V,v,C,c,A,a,S,s,Z and z commands.
Transformations and CSS units are not supported (only `user' units
are), and only a limited set of the CSS attributes are supported.

A number of connection points can be associated with the shape, which
are specified in the same coordinate system as the shape description.

A text box can be associated with the shape. The text box is also 
specified in the same coordinate system as the shape description. 

To choose size and position of the text box, you can think of one 
rectangle to contain the text box, and another one to  contain all 
other svg elements (call it the image rectangle): When you get the 
shape to the canvas, and write some text, all of it has to  go inside 
the text box; if necessary, this text box will grow, and, in the same 
proportion, the image rectangle will also grow.  

  

The rest is taken care of for you (resizing, moving, line connection,
loading, saving, undo, etc).


Shapes
======

A typical shape file may look something like this:
  <?xml version="1.0"?>

  <shape xmlns="http://www.daa.com.au/~james/dia-shape-ns"
         xmlns:svg="http://www.w3.org/2000/svg">
    <name>Circuit with identifiers - NPN Transistor</name>
    <icon>npn.xpm</icon>
    <connections>
      <point x="0" y="0"/>
      <point x="6" y="-4"/>
      <point x="6" y="4"/>
    </connections>

    <aspectratio type="fixed"/>

    <textbox x1="4" y1="-3" x2="12" y2="3" />

    <svg:svg>
      <svg:line x1="0" y1="0" x2="3" y2="0" />
      <svg:line x1="3" y1="-3" x2="3" y2="3" />
      <svg:line x1="3" y1="-2" x2="6" y2="-4" />
      <svg:line x1="3" y1="2" x2="6" y2="4" />

      <svg:polyline points="5,4 6,4 5.6154,3.0769" />
    </svg:svg>

  </shape>

Only the name and svg elements are required in the shape file.  The
rest are optional.

The name element give the name of the object.  The
name is a unique identifier for this shape that is used for saving and
loading. 

As in the example, you may use "compound names". Many shapes have first 
part of its name to indicate the sheet in which they appear, but this
is optional.
   
The icon element specifies an xpm file or a png file that is used as 
the icon in the dia toolbox.  The filename can be relative to the shape 
file.  If it is not given, a default custom shape icon will be used.

The connections section specifies a number of connection points for
the shape.  The coordinate system for these points is the same as the
coordinate system used in the svg shape description.

The aspectratio element allows you to specify how the shape can be
distorted.  The three possibilities are:
  <aspectratio type="free"/>    Any aspect ratio is OK (the default)
  <aspectratio type="fixed"/>   Fix the aspect ratio for this shape.
  <aspectratio type="range" min="n" max="m"/>  Give a range of values.

The last option allows you to specify a range of allowable amounts of
distortion, which may be useful in some cases.

The can-parent element allows to enable parenting for a shape. This is
only useful for rectangular shapes, which should work as a container
of other shapes or objects. So typical shapes wont have it.

The textbox element allows you to associate some text with
the shape.  The syntax is:
  <textbox x1="left" y1="top" x2="right" y2="bottom"/>
(Only one textbox per shape) Where the attributes give the bounds of 
the text box in the same coordinate system as the SVG shape description.

There are some optional attributes on <textbox/> namely
  resize="no" : by default the textbox is resized with the text
  align="center" : "center" is default, also "left" and "right" can be used

Shapes are given a default size on creation. If that default size does
not fit your needs you can overwrite it by (one or both):
  <default-width>1cm</default-width>
  <default-height>3cm</default-height>
The default unit "cm" can be omitted.

The svg element describes the shape.  The width and height attributes
are ignored, and only given to comply with the SVG specification.  For
more information on SVG, see the W3C pages about the format at:
  http://www.w3.org/Graphics/SVG/

The next section details what parts of the SVG spec can be used in
shape files.

The Shape Description
=====================

The Scalable Vector Graphics format is used to describe the shape.
That is why the separate namespace is used for that part of the file.

Each of the SVG drawing elements understands the style attribute.  The
attribute should be of the form:
  <svg:whatever style="name1: value1; name2: value2; ... name42: value42"/>

Currently only the following style attributes are understood:
  stroke-width - The width of the line, relative to the user specified
                 width.
  stroke-linecap    - The line cap style.  One of butt, round, square,
                      projecting (a synonym for square), or default.
  stroke-linejoin   - The line join style.  One of miter, round, bevel or
                      default.
  stroke-pattern    - The dash pattern.  One of none, dashed, dash-dot,
                      dash-dot-dot, dotted or default.
  stroke-dashlength - The length of the dashes in the dash pattern, in
                      relation to the user selected value (default is a
                      synonym for 1.0).
  stroke-opacity    - alpha value between 0..1.0
  fill-opacity      - alpha value between 0..1.0

  stroke       - The stroke colour.  You can use one of the symbolic
                 names foreground, fg, default, background, bg inverse,
                 text or none, or use a hex colour value of the form #rrggbb.
  fill         - The fill colour.  The same values as for stroke are used,
                 except that the meaning of default and inverse are
                 exchanged.  By default, elements are not filled, so to get
                 the default fill, use "fill: default"

So to draw a rectangle with a hairline stroke, the following would do
the trick:
  <svg:rect style="stroke-width: 0" x="..." y="..." width="..." height="..."/>

Ordinates x and y grow as in Dia. 

The recognised drawing elements are:

<svg:g>
  This is the group element.  You can place other drawing elements
  inside it.  The contents of the style attribute on a group element
  will propagate to the contained elements (unless they override it).

<svg:line x1="..." y1="..." x2="..." y2="..."/>
  This element is a line.

<svg:polyline points="...."/>
  This is a polyline.  That is, a number of connected line segments.
  The points attribute holds the coordinates of the end points for the
  line segments.  The coordinates are separated by white space or
  commas.  The suggested format is "x1,y1 x2,y2 x3,y3 ...".

<svg:polygon points="...."/>
  This is a polygon.  The points argument has the same format as the
  polyline.

<svg:rect x1="..." y1="..." width="..." height="..." rx="..." ry="..."/>
  This is a rectangle.  The upper left corner is (x1,y1), and the lower
  right corner is (x1+width,y1+height).
  To get rounded corners either rx or ry or both can be given for the
  single supported corner radius. If both are given the average gets
  used.

<svg:image x1="..." y1="..." width="..." height="..." xlink:href="..." />
  This is an external image.  The upper left corner is (x1,y1), and the 
  lower right corner is (x1+width,y1+height).
  Their are two forms of links supported, an absolute filename of the form
  "file:///home/user/image.png" or a relative one without the file:// prefix
  like in "image.png". The latter form is preferred because it is installation
  independent. The filename is relative to the shape file placement. In the
  above example PNG and shape need to be in the same directory.

  Inlined image data is also supported with xlink:href="data:image/png;base64,..."

<svg:circle cx="..." cy="..." r="..."/>
  This is a circle with centre (cx,cy) and radius r.

<svg:ellipse cx="..." cy="..." rx="..." ry="..."/>
  This is a ellipse with centre (cx, cy) and radius rx in the x direction
  and ry in the y direction.

<svg:path d="...."/>
  This is the most complicated drawing element.  It describes a path
  made up of line segments and bezier curves.  It currently does not
  support the elliptic arc or quadratic bezier curves.  The d string
  is made up of a number of commands of the form "x arg1 arg2 ..."
  where x is a character code identifying the command, and the
  arguments are numbers separated by white space or commas.  Each
  command has an absolute and relative variant.  The absolute one are
  spelled with an upper case letter. The relative ones are spelled with
  a lower case letter, and use the end point of the previous command
  as the origin.

  The supported commands are:
    M x,y                 Move cursor
    L x,y                 Draw a line to (x,y)
    H x                   Draw a horizontal line to x
    V y                   Draw a vertical line to y
    C x1,y1 x2,y2, x3,y3  Draw a bezier curve to (x3,y3) with (x1,y1)
                          and (x2,y2) as control points.
    S x1,y1 x2,y2         Same as above, but draw a `smooth' bezier.
                          That is, infer the first control point from
                          the previous bezier.
    Z                     Close the path.

  If the path is closed with z or Z, then it can be filled.
  Otherwise, it will just be drawn.

<svg:text x="..." y="..." style="...">...</svg:text>
  A text in the shape. The text has to be enclosed in the tags
  
  The parameters are:
  x,y			  The text position
  style			  Text formatting options
  
  The following style options are supported:
  font-size: font size in pt(?)  

Shapes in Shapes aka. Subshapes
===============================
Adding indepentently resizable symbols into your custom shapes is possible by
creating subshapes. This is done by some extra attributes on the group element.

<svg:g
 subshape="true"
 v_anchor="fixed.bottom"
 h_anchor="fixed.left"
 default_scale="1.0">

 v_anchor       The vertical anchoring of the subshape. Supported values are:
                "fixed.top", "fixed.bottom", "proportional"
 
 h_anchor       The horizontal anchoring of the subshape. Supported values are:
                "fixed.left", "fixed.right", "proportional"

 default_scale        currently unused

Extented Attributes
===================
To extend your custom shape with custom attributes you can put something like:

  <ext_attributes>
    <ext_attribute name="Integer" type="int" />
    <ext_attribute name="String" type="string" />
    <ext_attribute name="Float" type="real" />
  </ext_attributes>

between the <shape></shape> tags. The effect will be some custom properties
in your object. They are editable by the properties dialog and will be loaded 
and saved with your diagram. To programatically access them use "custom:<name>" 

The Sheet description
=====================

You can put several shapes in one sheet: the shapes you create  or any 
other shape or object "belonging" to other sheets.

A simple sheet file may look something as this:

<?xml version="1.0" encoding="utf-8"?> 
<sheet xmlns="http://www.lysator.liu.se/~alla/dia/dia-sheet-ns">
  <name>Circuit with identifiers</name>
  <name xml:lang="es">Circuito con identificadores</name>
  <description>Components for circuit diagrams</description>
  <description xml:lang="es">Componentes para diagramas de circuitos</description>
  <contents>
    
     <description>A bipolar npn transistor</description>
     <description xml:lang="es">Un transistor bipolar npn identificable</description>

     <description>An UML object</description>
     <description xml:lang="es">Un objeto UML</description>
    
   </contents>
</sheet>

How Dia helps to create and manage sheets and shapes.
=====================================================

You can use Dia with its available elements to draw a shape and then 
export it to a shape file, by using  
   File (of  diagram)->Export->By extension->Shape. 
But until now, this shapes  don't have any text box. (They are expected 
to manage some svg:text but not a text box). If you need one,  you can 
edit the file. 
Together with the shape file, you get a png file (after accepting the 
proposed size) which can be used for the shape's icon. 

By using
      File(of principal menu)->Sheets and Objects 
you can create  new sheets;  and add,  remove and parcially edit  shapes;
and copy or move shapes from one sheet to other.  

Design Notes
============

The custom shape code is designed so that a sheet of objects can be
self contained in a single directory.  Installing new shapes can be as
easy as untaring a .tar.gz file to ~/.dia/shapes or
$(prefix)/share/dia/shapes, with the sheet description going to 
~/.dia/sheets

If you have any suggestions for this code, please discuss on dia-list@gnome.org.

  James Henstridge <james@daa.com.au>
 with some modifications written by 
 Dolores Alia de Saravia<loli@unsa.edu.ar>     
