Fix to prevent undefined normals being generated with `add_face_normals()', from triangles with zero area.

2 files changed, 19 insertions, 5 deletions

diff --git a/intern/cycles/blender/blender_mesh.cpp b/intern/cycles/blender/blender_mesh.cpp
index e9250ec3eff..a01b2e9ee38 100644
--- a/intern/cycles/blender/blender_mesh.cpp
+++ b/intern/cycles/blender/blender_mesh.cpp
@@ -223,10 +223,19 @@ static void create_mesh(Scene *scene, Mesh *mesh, BL::Mesh b_mesh, const vector<
 		int shader = used_shaders[mi];
 		bool smooth = f->use_smooth();
 
-		mesh->add_triangle(vi[0], vi[1], vi[2], shader, smooth);
-
-		if(n == 4)
-			mesh->add_triangle(vi[0], vi[2], vi[3], shader, smooth);
+		if(n == 4) {
+			if(len_squared(cross(mesh->verts[vi[1]] - mesh->verts[vi[0]], mesh->verts[vi[2]] - mesh->verts[vi[0]])) == 0.0f ||
+				len_squared(cross(mesh->verts[vi[2]] - mesh->verts[vi[0]], mesh->verts[vi[3]] - mesh->verts[vi[0]])) == 0.0f) {
+				mesh->add_triangle(vi[0], vi[1], vi[3], shader, smooth);
+				mesh->add_triangle(vi[2], vi[3], vi[1], shader, smooth);
+			}
+			else {
+				mesh->add_triangle(vi[0], vi[1], vi[2], shader, smooth);
+				mesh->add_triangle(vi[0], vi[2], vi[3], shader, smooth);
+			}
+		}
+		else
+			mesh->add_triangle(vi[0], vi[1], vi[2], shader, smooth);
 
 		nverts.push_back(n);
 	}
diff --git a/intern/cycles/render/mesh.cpp b/intern/cycles/render/mesh.cpp
index a2d545d51c0..b20e5cebdc5 100644
--- a/intern/cycles/render/mesh.cpp
+++ b/intern/cycles/render/mesh.cpp
@@ -178,7 +178,12 @@ void Mesh::add_face_normals()
 			float3 v1 = verts_ptr[t.v[1]];
 			float3 v2 = verts_ptr[t.v[2]];
 
-			fN[i] = normalize(cross(v1 - v0, v2 - v0));
+			float3 norm = cross(v1 - v0, v2 - v0);
+			float normlen = len(norm);
+			if(normlen == 0.0f)
+				fN[i] = make_float3(0.0f, 0.0f, 0.0f);
+			else
+				fN[i] = norm / normlen;
 
 			if(flip)
 				fN[i] = -fN[i];