Saturday, April 21, 2012

Slow Progress + Issues

Worked on the code a bunch today. I'll quickly run through some of the issues.

Implemented the recursive tetrahedral outlined here. However, it is represented in points, and is not appropriate for this framework. So I decided to remove it. Below's a render of the fractal using the number of steps.

Next was to reverse my last change for the branch optimization that I blogged about. I just did a few tests and realized that when I flip the camera such that it is under the ground plane and it would only render black, I noticed a FPS increase of 2-3. This is because of screen space coherence and warp termination. There is branch diversion during whether it would render or not, and when enough pixels do not need to render, there is a performance increase.

Next I ported a knot shape code from the.savage's renderer from his renderer in GLSL Sandbox. Performance took a huge hit. Result below:

Then I realized that his renderer does something quite smart. He uses a circular bounding volume, and his renderer only renders what is inside the volume. It works for him since he only renders single floating objects in the middle of the screen. I implemented this into my own pipeline. It was a huge performance boost, over double the FPS. And if I zoom out such that the bounding volume occupies a even smaller portion of the screen, I see significant performance increase, from ~18 FPS to up to 90 FPS, again, due to coherency and warp termination. However, this technique is not too suitable for the types of images I'm trying to render since it crops only the center area of the scene. Here's a result:

I'll have to think about whether to use this technique, since it does provide a very significant performance boost.

Next, I discovered that my renderer has a huge issue in that for certain shapes when viewed from certain angles, there are banding / rippling distortion errors. I spent a long time looking at it but still cannot find the answer. I might have to go ahead without solving this issue since time is running out and I'd rather focus on other things. Here's an example:

Inline image 6

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