Mask BSDF: fix sampling weight to get correct gradients

mitsuba-renderer · Sep 25, 2023 · ee87f1c · ee87f1c
1 parent 7d91235
commit ee87f1c
Showing 1 changed file with 3 additions and 2 deletions.
diff --git a/src/bsdfs/mask.cpp b/src/bsdfs/mask.cpp
@@ -147,14 +147,15 @@ class MaskBSDF final : public BSDF<Float, Spectrum> {
         bs.sampled_component = null_index;
         bs.sampled_type      = +BSDFFlags::Null;
         bs.pdf               = 1.f - opacity;
-        result               = 1.f;
+        result               = (1.f - opacity) / dr::detach(1.f - opacity);
 
         Mask nested_mask = active && sample1 < opacity;
         if (dr::any_or<true>(nested_mask)) {
             sample1 /= opacity;
             auto tmp                = m_nested_bsdf->sample(ctx, si, sample1, sample2, nested_mask);
             dr::masked(bs, nested_mask) = tmp.first;
-            dr::masked(result, nested_mask) = tmp.second;
+            dr::masked(result, nested_mask) = tmp.second * opacity / dr::detach(opacity);
+            dr::masked(bs.pdf, nested_mask) *= opacity;
         }
 
         return { bs, result };