Fix T41116: Motion Blur causes random black surfaces on rigged models

Fix T41115: Motion Blur renders Objects Black - But not in Viewport Preview

This actually extends previous fix to normals and makes it all much nicer now.

Worth doing some intense testing, quick one worked just fine but there always
could be some corner cases.

intern/cycles/kernel/geom/geom_triangle.h

@@ -127,10 +127,7 @@ ccl_device_inline float3 triangle_normal(KernelGlobals *kg, ShaderData *sd)
 	float3 v2 = float4_to_float3(kernel_tex_fetch(__tri_verts, __float_as_int(tri_vindex.z)));
 	
 	/* return normal */
-	if(sd->flag & SD_NEGATIVE_SCALE_APPLIED)
-		return normalize(cross(v2 - v0, v1 - v0));
-	else
-		return normalize(cross(v1 - v0, v2 - v0));
+	return normalize(cross(v1 - v0, v2 - v0));
 }
 
 /* point and normal on triangle  */

intern/cycles/kernel/kernel_types.h

@@ -593,7 +593,6 @@ enum ShaderDataFlag {
 	SD_HOLDOUT_MASK = 524288,			/* holdout for camera rays */
 	SD_OBJECT_MOTION = 1048576,			/* has object motion blur */
 	SD_TRANSFORM_APPLIED = 2097152,		/* vertices have transform applied */
-	SD_NEGATIVE_SCALE_APPLIED = 4194304,	/* vertices have negative scale applied */
 
 	SD_OBJECT_FLAGS = (SD_HOLDOUT_MASK|SD_OBJECT_MOTION|SD_TRANSFORM_APPLIED)
 };

intern/cycles/render/mesh.cpp

@@ -341,6 +341,13 @@ void Mesh::add_vertex_normals()
 				vN[i] = -vN[i];
 		}
 	}
+	else if(flip) {
+		Attribute *attr_vN = attributes.find(ATTR_STD_VERTEX_NORMAL);
+		float3 *vN = attr_vN->data_float3();
+		for(size_t i = 0; i < verts_size; i++) {
+			vN[i] = -vN[i];
+		}
+	}
 
 	/* motion vertex normals */
 	Attribute *attr_mP = attributes.find(ATTR_STD_MOTION_VERTEX_POSITION);
@@ -375,6 +382,14 @@ void Mesh::add_vertex_normals()
 			}
 		}
 	}
+	else if(has_motion_blur() && attr_mN && flip) {
+		for(int step = 0; step < motion_steps - 1; step++) {
+			float3 *mN = attr_mN->data_float3() + step*verts.size();
+			for(size_t i = 0; i < verts_size; i++) {
+				mN[i] = -mN[i];
+			}
+		}
+	}
 }
 
 void Mesh::pack_normals(Scene *scene, float *tri_shader, float4 *vnormal)

intern/cycles/render/object.cpp

@@ -449,8 +449,6 @@ void ObjectManager::apply_static_transforms(DeviceScene *dscene, Scene *scene, u
 				}
 
 				object_flag[i] |= SD_TRANSFORM_APPLIED;
-				if(object->mesh->transform_negative_scaled)
-					object_flag[i] |= SD_NEGATIVE_SCALE_APPLIED;
 			}
 			else
 				have_instancing = true;