Cycles: compute triangle location from barycentric instead of re-intersecting

This is a bit more efficient than what we did before.

Ref D12954

4 files changed, 23 insertions, 215 deletions

diff --git a/intern/cycles/kernel/geom/motion_triangle_intersect.h b/intern/cycles/kernel/geom/motion_triangle_intersect.h
index cb6d210d90f..a11cb88385b 100644
--- a/intern/cycles/kernel/geom/motion_triangle_intersect.h
+++ b/intern/cycles/kernel/geom/motion_triangle_intersect.h
@@ -29,46 +29,19 @@
 
 CCL_NAMESPACE_BEGIN
 
-/* Refine triangle intersection to more precise hit point. For rays that travel
- * far the precision is often not so good, this reintersects the primitive from
- * a closer distance.
+/**
+ * Use the barycentric coordinates to get the intersection location
  */
-
-ccl_device_inline float3 motion_triangle_refine(KernelGlobals kg,
-                                                ccl_private ShaderData *sd,
-                                                float3 P,
-                                                float3 D,
-                                                float t,
-                                                const int isect_object,
-                                                const int isect_prim,
-                                                float3 verts[3])
+ccl_device_inline float3 motion_triangle_point_from_uv(KernelGlobals kg,
+                                                       ccl_private ShaderData *sd,
+                                                       const int isect_object,
+                                                       const int isect_prim,
+                                                       const float u,
+                                                       const float v,
+                                                       float3 verts[3])
 {
-#ifdef __INTERSECTION_REFINE__
-  if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
-    if (UNLIKELY(t == 0.0f)) {
-      return P;
-    }
-    const Transform tfm = object_get_inverse_transform(kg, sd);
-
-    P = transform_point(&tfm, P);
-    D = transform_direction(&tfm, D * t);
-    D = normalize_len(D, &t);
-  }
-
-  P = P + D * t;
-
-  /* Compute refined intersection distance. */
-  const float3 e1 = verts[0] - verts[2];
-  const float3 e2 = verts[1] - verts[2];
-  const float3 s1 = cross(D, e2);
-
-  const float invdivisor = 1.0f / dot(s1, e1);
-  const float3 d = P - verts[2];
-  const float3 s2 = cross(d, e1);
-  float rt = dot(e2, s2) * invdivisor;
-
-  /* Compute refined position. */
-  P = P + D * rt;
+  float w = 1.0f - u - v;
+  float3 P = u * verts[0] + v * verts[1] + w * verts[2];
 
   if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
     const Transform tfm = object_get_transform(kg, sd);
@@ -76,71 +49,8 @@ ccl_device_inline float3 motion_triangle_refine(KernelGlobals kg,
   }
 
   return P;
-#else
-  return P + D * t;
-#endif
 }
 
-/* Same as above, except that t is assumed to be in object space
- * for instancing.
- */
-
-#ifdef __BVH_LOCAL__
-#  if defined(__KERNEL_CUDA__) && (defined(i386) || defined(_M_IX86))
-ccl_device_noinline
-#  else
-ccl_device_inline
-#  endif
-    float3
-    motion_triangle_refine_local(KernelGlobals kg,
-                                 ccl_private ShaderData *sd,
-                                 float3 P,
-                                 float3 D,
-                                 float t,
-                                 const int isect_object,
-                                 const int isect_prim,
-                                 float3 verts[3])
-{
-#  if defined(__KERNEL_GPU_RAYTRACING__)
-  /* t is always in world space with OptiX and MetalRT. */
-  return motion_triangle_refine(kg, sd, P, D, t, isect_object, isect_prim, verts);
-#  else
-#    ifdef __INTERSECTION_REFINE__
-  if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
-    const Transform tfm = object_get_inverse_transform(kg, sd);
-
-    P = transform_point(&tfm, P);
-    D = transform_direction(&tfm, D);
-    D = normalize(D);
-  }
-
-  P = P + D * t;
-
-  /* compute refined intersection distance */
-  const float3 e1 = verts[0] - verts[2];
-  const float3 e2 = verts[1] - verts[2];
-  const float3 s1 = cross(D, e2);
-
-  const float invdivisor = 1.0f / dot(s1, e1);
-  const float3 d = P - verts[2];
-  const float3 s2 = cross(d, e1);
-  float rt = dot(e2, s2) * invdivisor;
-
-  P = P + D * rt;
-
-  if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
-    const Transform tfm = object_get_transform(kg, sd);
-    P = transform_point(&tfm, P);
-  }
-
-  return P;
-#    else  /* __INTERSECTION_REFINE__ */
-  return P + D * t;
-#    endif /* __INTERSECTION_REFINE__ */
-#  endif
-}
-#endif /* __BVH_LOCAL__ */
-
 /* Ray intersection. We simply compute the vertex positions at the given ray
  * time and do a ray intersection with the resulting triangle.
  */
diff --git a/intern/cycles/kernel/geom/motion_triangle_shader.h b/intern/cycles/kernel/geom/motion_triangle_shader.h
index fc7c181882e..15730c83969 100644
--- a/intern/cycles/kernel/geom/motion_triangle_shader.h
+++ b/intern/cycles/kernel/geom/motion_triangle_shader.h
@@ -68,15 +68,7 @@ ccl_device_noinline void motion_triangle_shader_setup(KernelGlobals kg,
   verts[1] = (1.0f - t) * verts[1] + t * next_verts[1];
   verts[2] = (1.0f - t) * verts[2] + t * next_verts[2];
   /* Compute refined position. */
-#ifdef __BVH_LOCAL__
-  if (is_local) {
-    sd->P = motion_triangle_refine_local(kg, sd, P, D, ray_t, isect_object, isect_prim, verts);
-  }
-  else
-#endif /* __BVH_LOCAL__*/
-  {
-    sd->P = motion_triangle_refine(kg, sd, P, D, ray_t, isect_object, isect_prim, verts);
-  }
+  sd->P = motion_triangle_point_from_uv(kg, sd, isect_object, isect_prim, sd->u, sd->v, verts);
   /* Compute face normal. */
   float3 Ng;
   if (sd->object_flag & SD_OBJECT_NEGATIVE_SCALE_APPLIED) {
diff --git a/intern/cycles/kernel/geom/shader_data.h b/intern/cycles/kernel/geom/shader_data.h
index f5055d8b285..2027190fdd2 100644
--- a/intern/cycles/kernel/geom/shader_data.h
+++ b/intern/cycles/kernel/geom/shader_data.h
@@ -89,7 +89,7 @@ ccl_device_inline void shader_setup_from_ray(KernelGlobals kg,
       sd->shader = kernel_tex_fetch(__tri_shader, sd->prim);
 
       /* vectors */
-      sd->P = triangle_refine(kg, sd, ray->P, ray->D, isect->t, isect->object, isect->prim);
+      sd->P = triangle_point_from_uv(kg, sd, isect->object, isect->prim, isect->u, isect->v);
       sd->Ng = Ng;
       sd->N = Ng;
 
diff --git a/intern/cycles/kernel/geom/triangle_intersect.h b/intern/cycles/kernel/geom/triangle_intersect.h
index 0169b40bc34..8458cf020a0 100644
--- a/intern/cycles/kernel/geom/triangle_intersect.h
+++ b/intern/cycles/kernel/geom/triangle_intersect.h
@@ -142,116 +142,23 @@ ccl_device_inline bool triangle_intersect_local(KernelGlobals kg,
 }
 #endif /* __BVH_LOCAL__ */
 
-/* Refine triangle intersection to more precise hit point. For rays that travel
- * far the precision is often not so good, this reintersects the primitive from
- * a closer distance. */
-
-/* Reintersections uses the paper:
- *
- * Tomas Moeller
- * Fast, minimum storage ray/triangle intersection
- * http://www.cs.virginia.edu/~gfx/Courses/2003/ImageSynthesis/papers/Acceleration/Fast%20MinimumStorage%20RayTriangle%20Intersection.pdf
+/**
+ * Use the barycentric coordinates to get the intersection location
  */
-
-ccl_device_inline float3 triangle_refine(KernelGlobals kg,
-                                         ccl_private ShaderData *sd,
-                                         float3 P,
-                                         float3 D,
-                                         float t,
-                                         const int isect_object,
-                                         const int isect_prim)
+ccl_device_inline float3 triangle_point_from_uv(KernelGlobals kg,
+                                                ccl_private ShaderData *sd,
+                                                const int isect_object,
+                                                const int isect_prim,
+                                                const float u,
+                                                const float v)
 {
-#ifdef __INTERSECTION_REFINE__
-  if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
-    if (UNLIKELY(t == 0.0f)) {
-      return P;
-    }
-    const Transform tfm = object_get_inverse_transform(kg, sd);
-
-    P = transform_point(&tfm, P);
-    D = transform_direction(&tfm, D * t);
-    D = normalize_len(D, &t);
-  }
-
-  P = P + D * t;
-
   const uint tri_vindex = kernel_tex_fetch(__tri_vindex, isect_prim).w;
   const packed_float3 tri_a = kernel_tex_fetch(__tri_verts, tri_vindex + 0),
                       tri_b = kernel_tex_fetch(__tri_verts, tri_vindex + 1),
                       tri_c = kernel_tex_fetch(__tri_verts, tri_vindex + 2);
-  float3 edge1 = make_float3(tri_a.x - tri_c.x, tri_a.y - tri_c.y, tri_a.z - tri_c.z);
-  float3 edge2 = make_float3(tri_b.x - tri_c.x, tri_b.y - tri_c.y, tri_b.z - tri_c.z);
-  float3 tvec = make_float3(P.x - tri_c.x, P.y - tri_c.y, P.z - tri_c.z);
-  float3 qvec = cross(tvec, edge1);
-  float3 pvec = cross(D, edge2);
-  float det = dot(edge1, pvec);
-  if (det != 0.0f) {
-    /* If determinant is zero it means ray lies in the plane of
-     * the triangle. It is possible in theory due to watertight
-     * nature of triangle intersection. For such cases we simply
-     * don't refine intersection hoping it'll go all fine.
-     */
-    float rt = dot(edge2, qvec) / det;
-    P = P + D * rt;
-  }
-
-  if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
-    const Transform tfm = object_get_transform(kg, sd);
-    P = transform_point(&tfm, P);
-  }
-
-  return P;
-#else
-  return P + D * t;
-#endif
-}
-
-/* Same as above, except that t is assumed to be in object space for
- * instancing.
- */
-ccl_device_inline float3 triangle_refine_local(KernelGlobals kg,
-                                               ccl_private ShaderData *sd,
-                                               float3 P,
-                                               float3 D,
-                                               float t,
-                                               const int isect_object,
-                                               const int isect_prim)
-{
-#if defined(__KERNEL_GPU_RAYTRACING__)
-  /* t is always in world space with OptiX and MetalRT. */
-  return triangle_refine(kg, sd, P, D, t, isect_object, isect_prim);
-#else
-  if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
-    const Transform tfm = object_get_inverse_transform(kg, sd);
-
-    P = transform_point(&tfm, P);
-    D = transform_direction(&tfm, D);
-    D = normalize(D);
-  }
+  float w = 1.0f - u - v;
 
-  P = P + D * t;
-
-#  ifdef __INTERSECTION_REFINE__
-  const uint tri_vindex = kernel_tex_fetch(__tri_vindex, isect_prim).w;
-  const packed_float3 tri_a = kernel_tex_fetch(__tri_verts, tri_vindex + 0),
-                      tri_b = kernel_tex_fetch(__tri_verts, tri_vindex + 1),
-                      tri_c = kernel_tex_fetch(__tri_verts, tri_vindex + 2);
-  float3 edge1 = make_float3(tri_a.x - tri_c.x, tri_a.y - tri_c.y, tri_a.z - tri_c.z);
-  float3 edge2 = make_float3(tri_b.x - tri_c.x, tri_b.y - tri_c.y, tri_b.z - tri_c.z);
-  float3 tvec = make_float3(P.x - tri_c.x, P.y - tri_c.y, P.z - tri_c.z);
-  float3 qvec = cross(tvec, edge1);
-  float3 pvec = cross(D, edge2);
-  float det = dot(edge1, pvec);
-  if (det != 0.0f) {
-    /* If determinant is zero it means ray lies in the plane of
-     * the triangle. It is possible in theory due to watertight
-     * nature of triangle intersection. For such cases we simply
-     * don't refine intersection hoping it'll go all fine.
-     */
-    float rt = dot(edge2, qvec) / det;
-    P = P + D * rt;
-  }
-#  endif /* __INTERSECTION_REFINE__ */
+  float3 P = u * tri_a + v * tri_b + w * tri_c;
 
   if (!(sd->object_flag & SD_OBJECT_TRANSFORM_APPLIED)) {
     const Transform tfm = object_get_transform(kg, sd);
@@ -259,7 +166,6 @@ ccl_device_inline float3 triangle_refine_local(KernelGlobals kg,
   }
 
   return P;
-#endif
 }
 
 CCL_NAMESPACE_END