a few differential geometry fixes, extended TriMesh::samplePosition() so that it also stores the UV coordinates

include/mitsuba/core/triangle.h

@@ -58,9 +58,10 @@ struct MTS_EXPORT_CORE Triangle {
 	 */
 	AABB getClippedAABB(const Point *positions, const AABB &aabb) const;
 
-	/// Uniformly sample a point on the triangle and return its normal
+	/// Uniformly sample a point on the triangle and return its normal and UV coordinates
 	Point sample(const Point *positions, const Normal *normals,
-			Normal &n, const Point2 &seed) const;
+			const Point2 *texCoords, Normal &n, Point2 &uv,
+			const Point2 &seed) const;
 
 	/// Calculate the surface area of this triangle
 	Float surfaceArea(const Point *positions) const;

src/libcore/triangle.cpp

@@ -22,7 +22,7 @@
 MTS_NAMESPACE_BEGIN
 
 Point Triangle::sample(const Point *positions, const Normal *normals,
-		Normal &normal, const Point2 &sample) const {
+		const Point2 *texCoords, Normal &normal, Point2 &uv, const Point2 &sample) const {
 	const Point &p0 = positions[idx[0]];
 	const Point &p1 = positions[idx[1]];
 	const Point &p2 = positions[idx[2]];
@@ -44,6 +44,17 @@ Point Triangle::sample(const Point *positions, const Normal *normals,
 		normal = Normal(normalize(cross(sideA, sideB)));
 	}
 
+	if (texCoords) {
+		const Point2 &uv0 = texCoords[idx[0]];
+		const Point2 &uv1 = texCoords[idx[1]];
+		const Point2 &uv2 = texCoords[idx[2]];
+
+		uv = uv0 * (1.0f - bary.x - bary.y) +
+			uv1 * bary.x + uv2 * bary.y;
+	} else {
+		uv = bary;
+	}
+
 	return p;
 }
 

src/librender/trimesh.cpp

@@ -367,7 +367,8 @@ void TriMesh::samplePosition(PositionSamplingRecord &pRec,
 
 	Point2 sample(_sample);
 	size_t index = m_areaDistr.sampleReuse(sample.y);
-	pRec.p = m_triangles[index].sample(m_positions, m_normals, pRec.n, sample);
+	pRec.p = m_triangles[index].sample(m_positions, m_normals,
+		m_texcoords, pRec.n, pRec.uv, sample);
 	pRec.pdf = m_invSurfaceArea;
 	pRec.measure = EArea;
 }

src/shapes/cylinder.cpp

@@ -210,12 +210,12 @@ public:
 
 		Vector dpdu = Vector(-local.y, local.x, 0) * (2*M_PI);
 		Vector dpdv = Vector(0, 0, m_length);
-		if (m_flipNormals)
-			dpdu *= -1;
 		its.shape = this;
 		its.dpdu = m_objectToWorld(dpdu);
 		its.dpdv = m_objectToWorld(dpdv);
 		its.geoFrame.n = Normal(normalize(cross(its.dpdu, its.dpdv)));
+		if (m_flipNormals)
+			its.geoFrame.n *= -1;
 		its.geoFrame.s = normalize(its.dpdu);
 		its.geoFrame.t = normalize(its.dpdv);
 		its.shFrame = its.geoFrame;

src/shapes/sphere.cpp

@@ -273,7 +273,7 @@ public:
 
 	void getNormalDerivative(const Intersection &its,
 			Vector &dndu, Vector &dndv, bool shadingFrame) const {
-		Float invRadius = 1.0f / m_radius;
+		Float invRadius = (m_flipNormals ? -1.0f : 1.0f) / m_radius;
 		dndu = its.dpdu * invRadius;
 		dndv = its.dpdv * invRadius;
 	}