20071025 - Motion Cards


(Lost all the Images)

Here is a shot from todays work. It is of a 360 degree fisheye projection of a few thousand motion cards rotating around the camera really really fast.

Triangle Reduction, From 4 to 1
Today I rewrote the motion card engine again, this time with a single triangle per motion card instead of 4. The aim here is to increase the efficiency of the geometry side of the engine now that I am planning on rendering 6 sides of a cubemap per frame. One thing I am guessing on is that when the GPU rasterizes small triangles which only cover a few pixels, that a chunk of SPUs are shading pixels which are not even in the polygon (since the GeForce 8 series has something like 8x4 fragment shader granularity). So changing from four tiny triangles per particle to one should provide somewhat of a performance boost in the fragment shading as well.

Ellipsoid Rendering
Anyone remember the Ecstatica game series from Psygnosis in 1997? Here is a screen shot,


The Atom engine is similar in concept, but taken to the next level. Instead of rendering with polygons, the basic primitive in the engine is an ellipsoid, limited to 2 radii instead of three. The motion card part of the engine composites the motion blurred ellipsoids into the framebuffer, and the rendering part of the engine turns each ellipsoid into a shaded impostor.

Here is a few flat shaded ellipsoid primatives (fisheye projection curves them).

Then a little motion.

Then a lot of motion.

And finally showing triangle primitives created by a large motion case.

The engine uses a alpha falloff under motion to insure a correct transparency for each moving particle.

What's Next
Still need to find a faster output path than the geometry shaders. I'm thinking of trying a trick to use transform feedback on points (one point per motion card) in a vertex shader and then output three interleaved attributes (for the triangle) in a VBO. Then later read in as a non-interleaved array of vertexes for triangles for all my cubemap passes.