Graphiti PlatformGraphicsAlgorithms

Graphiti's PlatformGraphicsAlgorithms allow the user to implement custom rendering for some shapes in a diagram. They are created just like any other GraphicsAlgorithm with the GaCreateService. When displayed, however, the diagram type provider is asked for a IGraphicsAlgorithmRendererFactory which in turn will be asked to create a IGraphicsAlgorithmRenderer for the specific PlatformGraphicsAlgorithm. The renderer interface is just a marker. The returned value can (or maybe even must) be a Draw2D object.

Example

Some code!
In the add feature where we want to create such a shape we will have something like:

import org.eclipse.graphiti.features.*;
import org.eclipse.graphiti.mm.pictograms.*;
import org.eclipse.graphiti.services.*;

public class SomeAddFeature extends AbstractAddFeature {
  // ... usual stuff (contructor, canAdd, etc)

  @Override
  public PictogramElement add(IAddContext context) {
    IPeCreateService peCreateService = Graphiti.getPeCreateService();
    Shape shape = peCreateService.createShape(context.getTargetContainer(), true);
    IGaCreateService gaCreateService = Graphiti.getGaCreateService();
    gaCreateService.createPlatformGraphicsAlgorithm(shape, "SOME_ID");

    link(shape, context.getNewObject());
    layoutPictogramElement(shape);
    return shape;
  }
}

As explained above we will also need an implementation of IGraphicsAlgorithmRendererFactory

import org.eclipse.graphiti.platform.ga.*;

public class GraphicsAlgorithmRendererFactory implements IGraphicsAlgorithmRendererFactory {

  @Override
  public IGraphicsAlgorithmRenderer createGraphicsAlgorithmRenderer(IRendererContext rendererContext) {
    String id = rendererContext.getPlatformGraphicsAlgorithm().getId();
    if ("SOME_ID".equals(id)) {
      return new SomeIdGARenderer();
    }
    return null;
  }
}

A new instance of this class has to be returned by the DiagramTypeProvider class upon calls to the getGraphicsAlgorithmRendererFactory method.

We still missing the implementation of the actual renderer.

import org.eclipse.draw2d.Graphics;
import org.eclipse.draw2d.Shape;
import org.eclipse.graphiti.platform.ga.IGraphicsAlgorithmRenderer;

public class SomeIdGARenderer extends Shape implements IGraphicsAlgorithmRenderer {

  @Override
  protected void fillShape(Graphics graphics) {
    // your code here
  }

  @Override
  protected void outlineShape(Graphics graphics) {
    // draw outline here
  }
}

More

• The example shows a GA used as the whole elements visual. PlatformGraphicsAlgorithms can obviously be used also in a PictogramElement composition.
• Since the renderer is a Figure, we can add children and use layouts.
• The minimum/maximum and preferred size of the renderer are not used to limit or initialize the bounds of the PictogramElement. Since PE are EObjects we could register an adapter and, at each change of location or size, query the renderer for the limits. (Never really tried this)