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.

An overview of the work done upto january on my thesis. My most recent work (on the GLSL implementation) is not included, this is all rendered using the CPU. The main differences with last video:

• Better viewport consistency by applying fading of the contour lines. (Reduces flicker effect)
• Optimalisation of suggestive contour rendering using an additional paper: Interactive Rendering of SC with Temporal Coherence (also from Decarlo et. al.)
• Quick and dirty implementation of suggestive highlights

Some more features implemented in my thesis project:

• Stroke fading (soft lines + anti-aliasing)
• Suggestive Highlights (still some tweaking – in combination with suggestive contours they give a false “embossed” impression)
• Various optimizations for time-coherent contours (see this follow-up paper). The ‘flickering’ issues I had with changing viewports have been reduced severely.
• Quick and dirty GUI for testing.

Unfortunately, no video yet, since recordmydesktop (even with the –full-shots switch), has issues recording OpenGL output in Ubuntu running in a Virtual Machine.

I thought it would be a nice experiment to log my progress on implementing suggestive contours for my thesis on a minute-by-minute basis.

Whether this turns out to be an interesting log or a boring concatenation of my sloppy coding adventures, we’ll see. I might discover what’s eating the most of my time …

Now works in every viewing direction. Up next: suggestive contours.

Some contour results.