HTrace RTAO vs. HDRP RTAO
Both algorithms feature the same ray-tracing implementation, which, due to its nature, converges to the same result. Given the same ray count and other parameters, they yield identical performance in the default configuration. Therefore, this comparison will focus on features (which affect performance) and denoising.
For these comparisons, the Sample (Ray) Count for both HDRP's RTAO and HTrace's RTAO was set to 4, and the Max Ray Length was set to 2.
Checkerboard Rendering
HTrace provides a Checkerboarding option that renders approximately 50% of pixels each frame and combines the final image over two consecutive frames. This approach significantly reduces the cost of the effect while keeping the visual output almost intact.
Alpha Cutout Evaluation
HTrace allows skipping hit material evaluation for rays, which can dramatically speed up ray-tracing performance. The only essential per-material feature for an effect like Ambient Occlusion is the alpha cutout, and HTrace provides an alternative solution by evaluating it in screen-space and falling back to a fully opaque geometry representation outside the frame.
Half Resolution
HTrace allows to disable full resolution tracing which can lead to up to 4x (resolution is downscaled 2X along each axis) performance boost. The final result can be upscaled to the target resolution with a FSR 1.0 inspired adaptive Lanczos filter augmented with bilateral weights.
By combining Checkerboard Rendering with Half Resolution and opting for Depth Test alpha cutout evaluation, we managed to reduce the performance time from 8.5 ms to 1.5 ms without decreasing the Ray Count or the Radius of occlusion.
Spatial Denoising
In the case of HDRP, all previous screenshots were made with the Denoiser Radius set to its minimum value of 0.01 for the sake of image quality. With such a small radius, there's almost no chance for denoising artifacts. However, according to HDRP's presets, this value is supposed to be at least 0.25 (Low), so for the next comparison, a value of 0.5 will be used, which corresponds to the Medium quality preset.
Unfortunately, as the radius grows, HDRP's RTAO yields progressively blurrier results, with many occlusion details destroyed by such aggressive denoising. Moreover, separate spatial samples become visible, forming distinctive lines and contours around geometric features.
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