Check Out Live Code!

Quite satisfied with the rendering results. Go to http://iamnop.com/raymarch/ for some nice real-time live code! (Hint: it's animated!)

Observed Performance Difference

With the full shading stack, rendering each frame becomes much more heavy, and performance differences become greater.

From observation, when viewport is mostly sky (far distances), the frame rate is about 30 fps. When the viewport is mostly ground or geometry (close distances), the frame rate jumps to about 50 fps. This is good news, since it implies that the ray marching loop is correctly optimized, where it successfully terminates when an intersection is found. I was not able to observe this difference until now.

Combined Render Passes

I have tweaked and fixed up various shading passes, and I think I am ready to move onto the modeling part of the project.

Here are the components of the shading:

1. Diffuse lighting
2. Soft shadows. Used instead of ray traced shadows. Also eliminates the need for ambient occlusion.
3. Subsurface scattering (so called). I figured it looks more like effects of depth volume rendering, not quite like subsurface scattering, but can account for some types of a similar effect.
4. Fog. Mainly used to hide numerical errors for large distances. Instead of light blue (or other fog color), can be set to black to simulate view-aligned lighting. 

Here's the current output:

Initial Subsurface Scattering

Implemented subsurface scattering based on sample code from Mazapan. The code again is similar to the technique for ambient occlusion. It samples distances along the marching ray. However, since it relies on negative sampled distance, it only works on signed distance fields (for example, it doesn't work with udBox).

Here's an initial result.

Soft Shadows

Implemented soft shadows. The technique is very similar to ambient occlusion. Instead of taking samples along the normal at the surface, it takes samples along the ray from the surface to the light. This roughly estimates the distances of the surrounding object to the ray of light, creating an effect very visually similar to soft shadows. Therefore, this is "fake" empirical soft shadows and is purely geometry based.

Here are some results of just the soft shadows component. I personally think they look very nice, and I am questioning the need for the diffuse lighting component at all.

Ambient Occlusion

Implemented ambient occlusion, based on method proposed by Iñigo Quilez. The method is originally based on another paper, "Fast Approximations for Global Illumination on Dynamic Scenes."

Here's how the method works: the ambient occlusion coefficient at each surface point is computed by taking samples of the distance field at varying distances above the point long its normal. This essentially estimates the "openness" of the region above the point. Here is a more formal mathematical description:

Here is an output of just the ambient occlusion term.

Here is ambient occlusion with diffused lighting.

Also, I want to point out that, with ambient occlusion implemented, there is an unintentional "skyline" effect where the ground plane ends. This could be because the ray does not intersect anything and therefore the normal is undefined at those points. However, it does provide a nice gradient visual effect, where before there were curved bands going across as a result of numerical errors. Here's a better picture of the "skyline".

Midpoint Presentation

See the slide deck for the midpoint presentation here.