The presentation i’ll be giving tomorrow

After squashing a rather nasty bug this morning (GLSL shader memory alloc is tricky), I made some renders to demonstrate the algorithm.

The algorithm is an object-space algorithm.  This has some implications: Operations are performed with direct vertex info. No intermediate rendering+signal filtering is done. Rendering it on the GPU makes it hard to control line width. This is the main disadvantage in using this algorithm over a CPU-implemented one. The main advantage is – of course – significant speedup in rendering.

The current version computes info for all vertices. I think I can speed things up a bit more by adding some additional tests in the vertex shader, which could signal the fragment shader that the fragment is unlikely to have contours. Whether or not the additional overhead of these tests is worth it, we’ll see. Pretty images behind the cut.

I don’t know what just happened to my shader, but this sure looks funky.

I’ve been trying to work out a good CPU-accelerated version the my suggestive contours algorithm during the last few weeks, and after working through some technical difficulties, I managed to compute and draw regular contour lines this afternoon:

Hard to see? I know,  it looks craptastic.

But after an afternoon of reading tutorials, bulletin boards and newsgroups, I know why. And I think it’s going to help me write a better thesis, so this delightful saturday wasn’t completely wasted. Conclusions behind the cut.

Today I rewrote parts of Trimesh2’s Mesh Viewer to work with GLSL-shaders. I implemented a simple cartoon shader. This is still pretty basic, since it doesn’t involve sending information back and forth between OpenGL and the shader.

Still, here is the result.

Because my current Suggestive Contours/Suggestive Highlights implementation is written using OpenGL calls for rendering, it was best to start work on the vertex/fragment shaders for a GPU implementation in the OpenGL shading language (GLSL). This would reduce OS/Platform dependency too. Another option was using Nvidia’s Cg, which claims to be compatible with an OpenGL renderer too, but documentation about this was scarce