Cycles: always perform backface culling for curve, remove option

The hair BSDFs are already designed to assume this, and disabling backface
culling would break them in some cases.

Ref T73778

Depends on D8009

Maniphest Tasks: T73778

Differential Revision: https://developer.blender.org/D8010

1 files changed, 37 insertions, 35 deletions

diff --git a/intern/cycles/bvh/bvh_embree.cpp b/intern/cycles/bvh/bvh_embree.cpp
index 4e064f54742..eb103b4e712 100644
--- a/intern/cycles/bvh/bvh_embree.cpp
+++ b/intern/cycles/bvh/bvh_embree.cpp
@@ -67,29 +67,9 @@ static_assert(Object::MAX_MOTION_STEPS == Geometry::MAX_MOTION_STEPS,
  * as well as filtering for volume objects happen here.
  * Cycles' own BVH does that directly inside the traversal calls.
  */
-static void rtc_filter_func(const RTCFilterFunctionNArguments *args)
-{
-  /* Current implementation in Cycles assumes only single-ray intersection queries. */
-  assert(args->N == 1);
-
-  const RTCRay *ray = (RTCRay *)args->ray;
-  const RTCHit *hit = (RTCHit *)args->hit;
-  CCLIntersectContext *ctx = ((IntersectContext *)args->context)->userRayExt;
-  KernelGlobals *kg = ctx->kg;
-
-  /* Check if there is backfacing hair to ignore. */
-  if (IS_HAIR(hit->geomID) && !(kernel_data.curve.curveflags & CURVE_KN_BACKFACING) &&
-      !(kernel_data.curve.curveflags & CURVE_KN_RIBBONS)) {
-    if (dot(make_float3(ray->dir_x, ray->dir_y, ray->dir_z),
-            make_float3(hit->Ng_x, hit->Ng_y, hit->Ng_z)) > 0.0f) {
-      *args->valid = 0;
-      return;
-    }
-  }
-}
-
 static void rtc_filter_occluded_func(const RTCFilterFunctionNArguments *args)
 {
+  /* Current implementation in Cycles assumes only single-ray intersection queries. */
   assert(args->N == 1);
 
   const RTCRay *ray = (RTCRay *)args->ray;
@@ -97,16 +77,6 @@ static void rtc_filter_occluded_func(const RTCFilterFunctionNArguments *args)
   CCLIntersectContext *ctx = ((IntersectContext *)args->context)->userRayExt;
   KernelGlobals *kg = ctx->kg;
 
-  /* For all ray types: Check if there is backfacing hair to ignore */
-  if (IS_HAIR(hit->geomID) && !(kernel_data.curve.curveflags & CURVE_KN_BACKFACING) &&
-      !(kernel_data.curve.curveflags & CURVE_KN_RIBBONS)) {
-    if (dot(make_float3(ray->dir_x, ray->dir_y, ray->dir_z),
-            make_float3(hit->Ng_x, hit->Ng_y, hit->Ng_z)) > 0.0f) {
-      *args->valid = 0;
-      return;
-    }
-  }
-
   switch (ctx->type) {
     case CCLIntersectContext::RAY_SHADOW_ALL: {
       /* Append the intersection to the end of the array. */
@@ -168,7 +138,7 @@ static void rtc_filter_occluded_func(const RTCFilterFunctionNArguments *args)
       }
 
       /* Ignore curves. */
-      if (hit->geomID & 1) {
+      if (IS_HAIR(hit->geomID)) {
         /* This tells Embree to continue tracing. */
         *args->valid = 0;
         break;
@@ -249,6 +219,34 @@ static void rtc_filter_occluded_func(const RTCFilterFunctionNArguments *args)
   }
 }
 
+static void rtc_filter_func_thick_curve(const RTCFilterFunctionNArguments *args)
+{
+  const RTCRay *ray = (RTCRay *)args->ray;
+  RTCHit *hit = (RTCHit *)args->hit;
+
+  /* Always ignore backfacing intersections. */
+  if (dot(make_float3(ray->dir_x, ray->dir_y, ray->dir_z),
+          make_float3(hit->Ng_x, hit->Ng_y, hit->Ng_z)) > 0.0f) {
+    *args->valid = 0;
+    return;
+  }
+}
+
+static void rtc_filter_occluded_func_thick_curve(const RTCFilterFunctionNArguments *args)
+{
+  const RTCRay *ray = (RTCRay *)args->ray;
+  RTCHit *hit = (RTCHit *)args->hit;
+
+  /* Always ignore backfacing intersections. */
+  if (dot(make_float3(ray->dir_x, ray->dir_y, ray->dir_z),
+          make_float3(hit->Ng_x, hit->Ng_y, hit->Ng_z)) > 0.0f) {
+    *args->valid = 0;
+    return;
+  }
+
+  rtc_filter_occluded_func(args);
+}
+
 static size_t unaccounted_mem = 0;
 
 static bool rtc_memory_monitor_func(void *userPtr, const ssize_t bytes, const bool)
@@ -652,7 +650,6 @@ void BVHEmbree::add_triangles(const Object *ob, const Mesh *mesh, int i)
   }
 
   rtcSetGeometryUserData(geom_id, (void *)prim_offset);
-  rtcSetGeometryIntersectFilterFunction(geom_id, rtc_filter_func);
   rtcSetGeometryOccludedFilterFunction(geom_id, rtc_filter_occluded_func);
   rtcSetGeometryMask(geom_id, ob->visibility_for_tracing());
 
@@ -825,8 +822,13 @@ void BVHEmbree::add_curves(const Object *ob, const Hair *hair, int i)
   update_curve_vertex_buffer(geom_id, hair);
 
   rtcSetGeometryUserData(geom_id, (void *)prim_offset);
-  rtcSetGeometryIntersectFilterFunction(geom_id, rtc_filter_func);
-  rtcSetGeometryOccludedFilterFunction(geom_id, rtc_filter_occluded_func);
+  if (use_ribbons) {
+    rtcSetGeometryOccludedFilterFunction(geom_id, rtc_filter_occluded_func);
+  }
+  else {
+    rtcSetGeometryIntersectFilterFunction(geom_id, rtc_filter_func_thick_curve);
+    rtcSetGeometryOccludedFilterFunction(geom_id, rtc_filter_occluded_func_thick_curve);
+  }
   rtcSetGeometryMask(geom_id, ob->visibility_for_tracing());
 
   rtcCommitGeometry(geom_id);