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Home » Eclipse Projects » GEF3D » Changes in GEF3D API
Changes in GEF3D API [message #562654] Tue, 04 August 2009 19:47
Kristian Duske is currently offline Kristian DuskeFriend
Messages: 64
Registered: July 2009
Hi everyone,

I just merged and committed an experimental branch we were working on
to the trunk. In this branch, Jens and I reimplemented the picking
mechanism in GEF3D and cleaned up everything that had to do with
coordinate systems and coordinate conversion. Since I am running a
little low on time due to my thesis, I will just sum up the most
significant changes:

1. Picking

Up until now, we used a technique called color picking (similar to
OpenGL selection mode) to determine which figure was at a given set of
mouse coordinates. This technique worked well, but has the major flaw
that you can only find the frontmost figure at any given location. If
you want to know what's behind that figure, you have to re-render the
color and depth buffers, and with that comes a big performance penalty.
The problem here is that GEF allows you to limit your search for a
figure at a given location using an instance of TreeSearch. For
example, if you want to know whether there's a handle at a certain
location, you'd ignore everything but the handle layer.

To support this in GEF3D, we had to rewrite the picking mechanism. We
did away with the color picking and now use the geometric data of the
figures and shapes to find intersections with a picking ray. This works
very well, has the desired flexibility when it comes to limiting a
search and is very fast even in larger diagrams. There is only one
downside, and that is that every figure must now implement the
interface org.eclipse.draw3d.picking.Pickable and its method

public float getDistance(Query i_query);

This method basically calculates the point of intersection between a
ray (stored in the given query) and the figure itself. This puts a
burden on framework users because if they want to use their own
figures, they have to implement this method, which requires a good
understanding of 3D math and such. To alleviate this, we will expand
our library of basic shapes, which are all pickable, and we will make
it easier for figures to simply be composed of a number of basic shapes
by introducing a ShapeFigure which delegates all rendering to one or
more shapes. This figure will also delegate the intersection detection
to the shapes, which will all implement this efficiently.

But even if someone cannot use Shapes and needs to write their own
rendering code, they will find that Math3D contains a number of very
useful functions for intersection detection, most notably
rayIntersectsPolygon, which does most of the heavy lifting.

In addition to this, we plan won writing a figure that can load polygon
models and display them in GEF3D, which would make it possible for
framework users to create their figures in a 3D editor like Maya and
then use them directly in GEF3D without any coding at all!

We hope that these tools and the improved performance and flexibility
that the new picking method gives us will make up for the added burden
of possible writing 3D math. But as we said, we will do what we can to
keep the math away from the users ;-)

2. Coordinate systems

With the new picking, we have introduced a trio of coordinate systems
that GEF3D uses, including simple methods of converting between them.
All this will be explained in a Wiki article I'm writing here:

The article is a work in progress and some of the information in there
is already out of date, but I will try to update it
tomorrow. The most important change we made is that
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