[EBOB-DISCUSS] found swt.graphics; it's a trade-off

[Liam M. <lm...@WP...>]

After looking through a few more SWT docs, I found a package I must have 
overlooked before -- org.eclipse.swt.graphics -- that handles drawing 
simple shapes. There's a class called GC that can draw rectangles, 
gradient rectangles, rounded rectangles, etc. However, it looks like it 
might be more difficult to use than GEF (though not impossible).

The key part of the existing code base, where all of this fits in, is 
ObjBenchView.createPartControl(Composite). This is the entry point to 
the view, where we get a reference to a "Composite" object, which as far 
as I can tell is more or less like a JComponent object, as far as its 
place in the heirarchy goes.

I've been looking into GEF the last few days (as you know), and it has a 
nice component-oriented system. You create a "Figure" (which is the 
parent class for different types of shapes, including RoundedRectangle) 
and add it to a FigureCanvas; the FigureCanvas is a go-between between 
the SWT Composite object and the GEF Figure objects. This makes it 
really easy to add/remove things; all you need to do is add these 
RoundedRectangles to the parent, and the layout manager handles their 
placement.

SWT's drawing is a little more like the AWT. You create a new GC object, 
using the passed-in Composite object's Display:
GC gc = new GC(parent.getDisplay());

Then you just call draw methods on the GC object, like this:
gc.drawRoundRectangle(int x, int y, int width, int height, int arcWidth, 
int arcHeight);

This is a little more difficult to deal with. Now the view is not only 
responsible for adding and removing, but for doing the drawing as well.. 
unless we go passing the gc object to the component to be added, in 
which case the component needs to be concerned about its placement. What 
happens if we remove the 2nd component out of 5? We'll have to worry 
about redrawing the other 3. As this is more low-level, it will be 
harder to code well, or rather we'll have to do more.

So there's a trade-off; do we stick with GEF, that makes everything 
easier, or do we write something around SWT, so that we don't force 
users to include extra plug-ins?