Thursday, April 12, 2012

Multiple Objects and Refractions

I've done a few things since the last blog post.

1) My ray stepping algorithm is now linear + binary search. What this means is I step my ray by large increments initially, detect when the ray's z-value is below the depth value, move my ray backwards, and decrease the step size. This is better than my previous approach of doing pure linear stepping because I can detect intersections faster and refine my results in less time.

2) Back-face rendering. I now use two framebuffer objects, one for front faces and one for back faces. Although this is somewhat slower than before, it makes reflections more accurate at certain angles.

3) Refractions. These were actually not that hard to do. Right now, the only difference between reflection and refraction in the shader is glsl refract vs reflect on the input ray. I might need to differentiate the two effects to be more physically accurate. I do not render refractive objects to the frame buffer because they would get in the way of the pixels behind.

4) Falloff. What I mean by this is the longer the ray must move to reflect an object, the more the reflected pixels fade. This lets me create objects that are cloudy or blurry, yet still reflective (not included in the demo below).

5) Lots of objects at once + physics (using Bullet)

What I need to do:

1) Improve visual quality. I've noticed that the reflected pixels get really jagged at around 45 degree angles to the surface. I'm still trying to figure out why this is happening. Also, I need to tweak my ray step algorithm to find the right balance between speed and accuracy.

2) Fresnel reflection. Reflection and refraction should adjust based on the view angle (assuming an object is both reflective and refractive).

3) I don't know if this is feasible for a couple reasons, but I would like to try out a linked list fragment structure for extremely accurate reflections. This would get rid of the ugly shadows when the reflective object covers the wall behind it. Unfortunately, this technique has high memory consumption. More details on this technique from Sean Lilley's blog:

Anyway, there is still a good amount to work to do but I thought I would show a demo of my progress:
Note: The fps drops to around 40 when I'm really zoomed in, but otherwise it is 60+

1 comment:

  1. Great work so far Ian. I agree with your road map, #1 and #2 are the most important; however, #2 is probably easier.

    Are any of the traditional techniques used to improve the visual quality of shadows useful to you?