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Protect against degenerate (zero area) mesh light faces (#2257) #21

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Protect against degenerate (zero area) mesh light faces (#2257) #21

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38 changes: 26 additions & 12 deletions lib/rendering/pbr/light/MeshLight.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -805,7 +805,11 @@ MeshLight::setMesh(geom::internal::Primitive* prim)
}
}
mArea += area;
faces[f].mInvArea = 1 / area;
// Guard against degenerate (zero-area) faces storing inf in mInvArea.
// Ideally, zero-area (which are also zero energy) faces will not be chosen.
// However, if both branches have zero energy, we choose one branch randomly
// (see the edge case in drawSampleRecurse). This guard prevents inf from propagating.
faces[f].mInvArea = (area > 0.0f) ? (1.0f / area) : 0.0f;

// get energy
// TODO: more fine detail on texture sampling? Take average instead of max?
Expand Down Expand Up @@ -1633,8 +1637,9 @@ MeshLight::intersect(const scene_rdl2::math::Vec3f &p, const scene_rdl2::math::V
}

bool
MeshLight::sample(const scene_rdl2::math::Vec3f &p, const scene_rdl2::math::Vec3f *n, float time, const scene_rdl2::math::Vec3f& r,
scene_rdl2::math::Vec3f &wi, LightIntersection &isect, float rayDirFootprint) const
MeshLight::sample(const scene_rdl2::math::Vec3f &p, const scene_rdl2::math::Vec3f *n, float time,
const scene_rdl2::math::Vec3f& r, scene_rdl2::math::Vec3f &wi, LightIntersection &isect,
float rayDirFootprint) const
{
MNRY_ASSERT(mOn);

Expand All @@ -1654,7 +1659,10 @@ MeshLight::sample(const scene_rdl2::math::Vec3f &p, const scene_rdl2::math::Vec3
faceIndex = drawSampleRecurse(transformedP, nullptr, 0, r3, pdf);
}

MNRY_ASSERT(scene_rdl2::math::isfinite(pdf) && pdf >= 0.0f);
MNRY_ASSERT(scene_rdl2::math::isfinite(pdf) && pdf > 0.0f);
if (!scene_rdl2::math::isfinite(pdf) || pdf <= 0.0f) {
return false;
}
MNRY_ASSERT(mBVH[faceIndex].isLeaf());
const Face& face = *mBVH[faceIndex].mFace;

Expand All @@ -1668,6 +1676,20 @@ MeshLight::sample(const scene_rdl2::math::Vec3f &p, const scene_rdl2::math::Vec3
scene_rdl2::math::Vec3f p2 = getFaceVertex(face, 1, time);
scene_rdl2::math::Vec3f p3 = getFaceVertex(face, 2, time);

if (mDeformationMb) {
const scene_rdl2::math::Vec3f crossProd = cross(p2 - p1, p3 - p1);
const float crossLen = length(crossProd);
// Handle degenerate, zero-area triangles
if (crossLen < scene_rdl2::math::sEpsilon) {
return false;
}
// We cannot directly use face.mNormal here because it is the normal at
// time = centroidTime. Therefore we compute it here.
normal = crossProd / crossLen;
} else {
normal = face.mNormal;
}

// the random numbers r1 and r2 can be used as uv coordinates
float u = r1;
float v = r2;
Expand All @@ -1680,14 +1702,6 @@ MeshLight::sample(const scene_rdl2::math::Vec3f &p, const scene_rdl2::math::Vec3
}
hit = w*p1 + u*p2 + v*p3;

if (mDeformationMb) {
// We cannot directly use face.mNormal here because it is the normal at
// time = centroidTime. Therefore we compute it here.
normal = normalize(cross(p2 - p1, p3 - p1));
} else {
normal = face.mNormal;
}

if (mMapShader) {
// get barycentric coordinate for hit
uv.x = u;
Expand Down
27 changes: 18 additions & 9 deletions lib/rendering/pbr/light/MeshLight.ispc
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Original file line number Diff line number Diff line change
Expand Up @@ -397,7 +397,10 @@ MeshLight_sample(const uniform Light * uniform li,
faceIndex = MeshLight_drawSampleRecurse(light, transformedP, nullptr, 0, r3, pdf);
}

MNRY_ASSERT(isfinite(pdf) && pdf >= 0.0f);
MNRY_ASSERT(isfinite(pdf) && pdf > 0.0f);
if (!isfinite(pdf) || pdf <= 0.0f) {
return false;
}
MNRY_ASSERT(Node_isLeaf(&light->mBVHPtr[faceIndex]));

const uniform Face * varying face = light->mBVHPtr[faceIndex].mFace;
Expand All @@ -412,6 +415,20 @@ MeshLight_sample(const uniform Light * uniform li,
Vec3f p2 = MeshLight_getFaceVertex(light, face, 1, time);
Vec3f p3 = MeshLight_getFaceVertex(light, face, 2, time);

if (light->mDeformationMb) {
const Vec3f crossProd = cross(p2 - p1, p3 - p1);
const float crossLen = length(crossProd);
// Handle degenerate, zero-area triangles
if (crossLen < sEpsilon) {
return false;
}
// We cannot directly use face.mNormal here because it is the normal at
// time = centroidTime. Therefore we compute it here.
normal = crossProd / crossLen;
} else {
normal = face->mNormal;
}

// the random numbers r1 and r2 can be used as uv coordinates
float u = r1;
float v = r2;
Expand All @@ -424,14 +441,6 @@ MeshLight_sample(const uniform Light * uniform li,
}
hit = w*p1 + u*p2 + v*p3;

if (light->mDeformationMb) {
// We cannot directly use face.mNormal here because it is the normal at
// time = centroidTime. Therefore we compute it here.
normal = normalize(cross(p2 - p1, p3 - p1));
} else {
normal = face->mNormal;
}

if (light->mMapShader) {
// get barycentric coordinate for hit
uv.x = u;
Expand Down