HDR Environment Map Improvements

I made some improvements to my HDR bitmap environment map system to make it more robust, fix a couple little bugs. and make it faster. For testing, I made an 8x4 pixel equirectangular environment map in OpenEXR format, then I used my equirectangular camera to render some pictures of an object using the environment map as a light source. This way, I was able to see the entire environment, what my linear interpolation smoothing was doing, and how the object was being lit.

An enlarged PNG version of the 8x4 pixel OpenEXR environment map.

Here are the final results of my tests, after I made all of the improvements and fixes:

No smoothing. BRDF-based distribution path tracing.

No smoothing. Direct illumination using environment map importance sampling.

Linear interpolation. BRDF-based distribution path tracing.

Linear interpolation. Direct illumination using environment map importance sampling.

You might notice some subtle colored strips on the edges of these images. That's due to anti-aliasing and jittering (of the output image, not the environment map) which, when combined with the equirectangular mapping, cause some samples to end up on the other edges.