22.6 Walkthrough: Creating Your Own Shapes

You can create your own shapes and include them in your own sheet simply be defining the shapes in XML (using a subset of SVG, the scalable vector graphics format based on XML). Installing a new shape is simply a matter of installing it into ~/.dia/shapes.

22.6.1 Simple Example

A shape consists of at least a name and a SVG element. That is, every shape, at a minimum, has a name and a description:

<?xml version="1.0"?>

<shape xmlns="http://www.daa.com.au/~james/dia-shape-ns"
  <name>Sample - Minimal Shape</name>
  <svg:svg width="10" height="10">
    <svg:polygon points="0,0 10,0 5,10"/>

You can place this in a subdirectory of your own dia shapes directory, perhaps called Sample as in ~/.dia/shapes/Sample/minimal.shape. The actual filename in which the shape is stored (minimal.shape) is not so important—dia will find the file.

Now you need to create a sheet into which this shape is placed. Again, a sheet is specified using XML. This example is placed in the file ~/.dia/sheets/Sample.sheet:

<?xml version="1.0" encoding="iso-8859-1"?>

<sheet xmlns="http://www.lysator.liu.se/~alla/dia/dia-sheet-ns">
  <description>A collection of sample shapes.</description>
    <object name="Sample - Minimal Shape">
      <description>The most minimal of shapes</description>

Now start up dia and you should see this new sheet, called Sample, containing a single button with a default icon. %

You can now create a new canvas and add this shape to your canvas. Note that dia takes care of the resizing of the shape and the other characteristics.

The XML describing the shape begins with the usual xml meta element followed the actual shape element, identifying the appropriate XML namespaces (xmlns). The shape has a unique name used to identify the shape by dia. Next we have the actual SVG description of the shape which is 10 by 10 in size % (actually these are ignored by dia but are required by the SVG format), and consisting of a single polygon. The shape is a simple triangle (a polygon with three points) pointing downwards. The polygon is drawn from the top left corner (0,0) to the top right (10,0) then to the bottom middle (5,10) and then back to the top left to finish off the polygon.

The XML for the sheet then identifies this shape as belonging to the Sample sheet, which contains just one object, the Sample - Minimal Shape shape. The description for the object is used as the tooltip for the resulting button.

22.6.2 Shape Elements

An icon can be associated with the shape through the icon element. An example is:


% which comes after the name element. The specified X pixmap file is used as the icon in the dia toolbox. The filename can be relative to the shape file (e.g., icons/minimal.xpm or ../icons/minimal.xpm). When no icon is specified a default icon is used. %

Connection points can be added to the shape with the connections element which allows any number of point elements. For example you can add two connection points to the above Minimal Shape by inserting the following after the icon element (or after the name element if there is no icon element):

    <point x="5" y="0"/>
    <point x="5" y="10"/>

% This adds a connection point to the top and another to the bottom of the triangle. The coordinate system used for connection points is the same as for the shape itself.

Next an aspectratio element can be specified to indicate how the shape is to be distorted. The default is as if the following was specified:

  <aspectratio type="free"/>

This indicates that there is no restriction on the aspect ratio (i.e., you can stretch the shape arbitrarily in the X and Y directions independently). A fixed aspect ratio requires Y to change in the same proportion as X, and vice versa. A range can be specified, with two attributes, min and max, identifying a range of allowable amounts of distortion. For example,

  <aspectratio type="range" min="4" max="8"/>

A textbox element can appear next. This is used to provide a box that automatically adjusts the size of the shape to fit the supplied text. The location of the text box is specified using the same coordinate system:

  <textbox x1="2" y1="1" x2="8" y2="5"/>

22.6.3 SVG Support

From SVG the supported elements are: line, polyline, polygon, rect, circle, ellipse, path and g. For the path element only the M, m, L, l, H, h, V, v, C, c, S, s, Z, and z commands are supported. User units are supported but not CSS units (only a limited set of the CSS attributes are supported). Transformations are not supported.

%### Sheet Elements

22.6.4 Installing New Sheets

Sheets are often distributed as compressed tar files (having the filename extension of .tar.gz). To install the sheet (assuming the tar file has been created properly) open the tar file in the GNOME archive tool (guitar). Select all files in the archive (Ctl+A or Archive\(\rightarrow\)Select all) then click the Extract button. You will be asked where to extract the files to—choose the .dia folder in your home directory.

Next time you start up dia the new sheet will be available.

%## Reference: The dia Save Format

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