Image Based Lighting is used to implement ambient lighting for dynamic objects coming from static objects in a game level. In most cases, it is used for specular lighting or reflections. In this process lighting information at the potential point of interests is stored in a special type of cube maps called Light probes. These Light probes are created using environment maps captured at same locations, which are then blurred in some special way depending on the BRDF  that will consume them at runtime. Each mipmap of a light probe contains a version of environment map blurred by a different amount depending roughness represented by that level. For example, if we are using 10 mip map levels to represent roughness from 0 to 1, then mip-0 will be blurred by a value representing roughness 0, mip-1 will represent 0.1 and so on. The last mip level mip-10 will be blurred by a value represent the roughness of 1.0. This process is also called Cubemap Convolution . All of this is done as a pre-process and resulting light probes are fetched at runtime to enable reflections or Image Based Lighting.
From past few weeks, I have been working on Image Based Lighting. Finally, I have finished writing features to generate dynamic cube maps and generate pre-convoluted probes for both diffuse (lambert) and GGX based specular.
Still there’s a lot of work to do. Here’s some rough list of features(or problems) I will be working on next:
- Support for many IBL probes – I am thinking maybe 32
- Choosing IBL probe (probes) to be used for the current pixel being shaded – I am thinking to maybe implement something similar to point light selection using tiled rendering or something. I can just replace point light calculation with cube map sampling for IBL. This way I can store all probes in a single array can bind all IBL probes to the single slot. I think this would be faster than checking the closest IBL probe for every object and passing it while shading. (Same benefits as deferred rendering over forward)
- Parallax correction for local probes
- Realtime IBL probes? – I don’t know if I would need this or SSR would be good enough.
- Fix seams for lower MIP levels. I am not sure whether I should implement parabolic maps or code some other techniques like wrap, or something.
- Improve Pre-convolution performance by further randomizing the samples and use less number of samples.