Cycles: switch Cycles triangle barycentric convention to match Embree/OptiX

Simplifies intersection code a little and slightly improves precision regarding
self intersection.

The parametric texture coordinate in shader nodes is still the same as before
for compatibility.

4 files changed, 18 insertions, 24 deletions

diff --git a/intern/cycles/kernel/device/cpu/bvh.h b/intern/cycles/kernel/device/cpu/bvh.h
index 8ebeee99c47..6c06232a692 100644
--- a/intern/cycles/kernel/device/cpu/bvh.h
+++ b/intern/cycles/kernel/device/cpu/bvh.h
@@ -166,16 +166,16 @@ ccl_device_inline void kernel_embree_convert_hit(KernelGlobals kg,
   }
   else {
     isect->type = kernel_data_fetch(objects, isect->object).primitive_type;
-    isect->u = 1.0f - hit->v - hit->u;
-    isect->v = hit->u;
+    isect->u = hit->u;
+    isect->v = hit->v;
   }
 }
 
 ccl_device_inline void kernel_embree_convert_sss_hit(
     KernelGlobals kg, const RTCRay *ray, const RTCHit *hit, Intersection *isect, int object)
 {
-  isect->u = 1.0f - hit->v - hit->u;
-  isect->v = hit->u;
+  isect->u = hit->u;
+  isect->v = hit->v;
   isect->t = ray->tfar;
   RTCScene inst_scene = (RTCScene)rtcGetGeometryUserData(
       rtcGetGeometry(kernel_data.device_bvh, object * 2));
diff --git a/intern/cycles/kernel/device/metal/bvh.h b/intern/cycles/kernel/device/metal/bvh.h
index f30b21abaf9..03faa3f020f 100644
--- a/intern/cycles/kernel/device/metal/bvh.h
+++ b/intern/cycles/kernel/device/metal/bvh.h
@@ -129,9 +129,8 @@ ccl_device_intersect bool scene_intersect(KernelGlobals kg,
 
   isect->t = intersection.distance;
   if (intersection.type == intersection_type::triangle) {
-    isect->u = 1.0f - intersection.triangle_barycentric_coord.y -
-               intersection.triangle_barycentric_coord.x;
-    isect->v = intersection.triangle_barycentric_coord.x;
+    isect->u = intersection.triangle_barycentric_coord.x;
+    isect->v = intersection.triangle_barycentric_coord.y;
   }
   else {
     isect->u = payload.u;
@@ -346,9 +345,8 @@ ccl_device_intersect bool scene_intersect_volume(KernelGlobals kg,
 
   isect->t = intersection.distance;
   if (intersection.type == intersection_type::triangle) {
-    isect->u = 1.0f - intersection.triangle_barycentric_coord.y -
-               intersection.triangle_barycentric_coord.x;
-    isect->v = intersection.triangle_barycentric_coord.x;
+    isect->u = intersection.triangle_barycentric_coord.x;
+    isect->v = intersection.triangle_barycentric_coord.y;
   }
   else {
     isect->u = payload.u;
diff --git a/intern/cycles/kernel/device/metal/kernel.metal b/intern/cycles/kernel/device/metal/kernel.metal
index b295e081f3f..3d173b0d601 100644
--- a/intern/cycles/kernel/device/metal/kernel.metal
+++ b/intern/cycles/kernel/device/metal/kernel.metal
@@ -122,8 +122,8 @@ TReturn metalrt_local_hit(constant KernelParamsMetal &launch_params_metal,
   isect->object = object;
   isect->type = kernel_data_fetch(objects, object).primitive_type;
 
-  isect->u = 1.0f - barycentrics.y - barycentrics.x;
-  isect->v = barycentrics.x;
+  isect->u = barycentrics.x;
+  isect->v = barycentrics.y;
 
   /* Record geometric normal */
   const uint tri_vindex = kernel_data_fetch(tri_vindex, isect->prim).w;
@@ -185,18 +185,14 @@ bool metalrt_shadow_all_hit(constant KernelParamsMetal &launch_params_metal,
     return true;
   }
 
-  float u = 0.0f, v = 0.0f;
+  const float u = barycentrics.x;
+  const float v = barycentrics.y;
   int type = 0;
   if (intersection_type == METALRT_HIT_TRIANGLE) {
-    u = 1.0f - barycentrics.y - barycentrics.x;
-    v = barycentrics.x;
     type = kernel_data_fetch(objects, object).primitive_type;
   }
 #  ifdef __HAIR__
   else {
-    u = barycentrics.x;
-    v = barycentrics.y;
-
     const KernelCurveSegment segment = kernel_data_fetch(curve_segments, prim);
     type = segment.type;
     prim = segment.prim;
diff --git a/intern/cycles/kernel/device/optix/bvh.h b/intern/cycles/kernel/device/optix/bvh.h
index 0fb8156c27d..d1d342f6034 100644
--- a/intern/cycles/kernel/device/optix/bvh.h
+++ b/intern/cycles/kernel/device/optix/bvh.h
@@ -116,8 +116,8 @@ extern "C" __global__ void __anyhit__kernel_optix_local_hit()
   isect->type = kernel_data_fetch(objects, isect->object).primitive_type;
 
   const float2 barycentrics = optixGetTriangleBarycentrics();
-  isect->u = 1.0f - barycentrics.y - barycentrics.x;
-  isect->v = barycentrics.x;
+  isect->u = barycentrics.x;
+  isect->v = barycentrics.y;
 
   /* Record geometric normal. */
   const uint tri_vindex = kernel_data_fetch(tri_vindex, prim).w;
@@ -152,8 +152,8 @@ extern "C" __global__ void __anyhit__kernel_optix_shadow_all_hit()
   int type = 0;
   if (optixIsTriangleHit()) {
     const float2 barycentrics = optixGetTriangleBarycentrics();
-    u = 1.0f - barycentrics.y - barycentrics.x;
-    v = barycentrics.x;
+    u = barycentrics.x;
+    v = barycentrics.y;
     type = kernel_data_fetch(objects, object).primitive_type;
   }
 #  ifdef __HAIR__
@@ -336,8 +336,8 @@ extern "C" __global__ void __closesthit__kernel_optix_hit()
 
   if (optixIsTriangleHit()) {
     const float2 barycentrics = optixGetTriangleBarycentrics();
-    optixSetPayload_1(__float_as_uint(1.0f - barycentrics.y - barycentrics.x));
-    optixSetPayload_2(__float_as_uint(barycentrics.x));
+    optixSetPayload_1(__float_as_uint(barycentrics.x));
+    optixSetPayload_2(__float_as_uint(barycentrics.y));
     optixSetPayload_3(prim);
     optixSetPayload_5(kernel_data_fetch(objects, object).primitive_type);
   }