Add GLSL functions for PDFs#2779
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jstone-lucasfilm merged 4 commits intoAcademySoftwareFoundation:mainfrom Feb 19, 2026
Merged
Add GLSL functions for PDFs#2779jstone-lucasfilm merged 4 commits intoAcademySoftwareFoundation:mainfrom
jstone-lucasfilm merged 4 commits intoAcademySoftwareFoundation:mainfrom
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This changelist adds explicit GLSL functions for PDFs (probability density functions) to MaterialX, making its physically based shading code clearer and more self-documenting, and providing a stepping stone towards future use of generated GLSL/ESSL/MSL in path tracers as well as rasterization renderers.
Following up on a conversation with Stephen Hill, this update clarifies the name and description of `mx_ggx_VNDF_reflection_PDF`, which represents the PDF of a reflection direction sampled from the GGX VNDF.
| // uniform_pdf = 1 / (2 * PI) | ||
| // radiance = reflectance * NdotL / uniform_pdf; | ||
| radiance += reflectance * NdotL * 2.0 * M_PI; | ||
| radiance += reflectance * NdotL / mx_uniform_hemisphere_PDF(); |
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I guess this new division is easy for the compiler to remove since the PDF function returns a constant.
niklasharrysson
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This looks good to me!
shill-lucasfilm
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As discussed offline, we should probably add a mx_ggx_VNDF_PDF() function that directly corresponds to the sampling function (which maybe mx_generate_prefilter_env() could use, since unlike mx_environment_radiance(), it's not performance critical), and also update a few functions to handle anisotropy correctly. However, those changes are out of scope for this PR, so I'll prep a new one soon.
jstone-lucasfilm
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This changelist adds explicit GLSL functions for PDFs (probability density functions) to MaterialX, making its physically based shading code clearer and more self-documenting, and providing a stepping stone towards future use of generated GLSL/ESSL/MSL in path tracers as well as rasterization renderers.