Fix T99201: Cycles render difference with 3D hair curves between OptiX and Emrbee

It should consistently use the Cycles pirmitive ID for self intersection detection,
not the one from the OptiX or Embree acceleration structure.

Differential Revision: https://developer.blender.org/D15632

1 files changed, 22 insertions, 12 deletions

diff --git a/intern/cycles/kernel/device/cpu/bvh.h b/intern/cycles/kernel/device/cpu/bvh.h
index 6c06232a692..d9267e1cd6d 100644
--- a/intern/cycles/kernel/device/cpu/bvh.h
+++ b/intern/cycles/kernel/device/cpu/bvh.h
@@ -114,27 +114,37 @@ ccl_device_inline bool kernel_embree_is_self_intersection(const KernelGlobals kg
                                                           const RTCHit *hit,
                                                           const Ray *ray)
 {
-  bool status = false;
+  int object, prim;
+
   if (hit->instID[0] != RTC_INVALID_GEOMETRY_ID) {
-    const int oID = hit->instID[0] / 2;
-    if ((ray->self.object == oID) || (ray->self.light_object == oID)) {
+    object = hit->instID[0] / 2;
+    if ((ray->self.object == object) || (ray->self.light_object == object)) {
       RTCScene inst_scene = (RTCScene)rtcGetGeometryUserData(
           rtcGetGeometry(kernel_data.device_bvh, hit->instID[0]));
-      const int pID = hit->primID +
-                      (intptr_t)rtcGetGeometryUserData(rtcGetGeometry(inst_scene, hit->geomID));
-      status = intersection_skip_self_shadow(ray->self, oID, pID);
+      prim = hit->primID +
+             (intptr_t)rtcGetGeometryUserData(rtcGetGeometry(inst_scene, hit->geomID));
+    }
+    else {
+      return false;
     }
   }
   else {
-    const int oID = hit->geomID / 2;
-    if ((ray->self.object == oID) || (ray->self.light_object == oID)) {
-      const int pID = hit->primID + (intptr_t)rtcGetGeometryUserData(
-                                        rtcGetGeometry(kernel_data.device_bvh, hit->geomID));
-      status = intersection_skip_self_shadow(ray->self, oID, pID);
+    object = hit->geomID / 2;
+    if ((ray->self.object == object) || (ray->self.light_object == object)) {
+      prim = hit->primID +
+             (intptr_t)rtcGetGeometryUserData(rtcGetGeometry(kernel_data.device_bvh, hit->geomID));
     }
+    else {
+      return false;
+    }
+  }
+
+  const bool is_hair = hit->geomID & 1;
+  if (is_hair) {
+    prim = kernel_data_fetch(curve_segments, prim).prim;
   }
 
-  return status;
+  return intersection_skip_self_shadow(ray->self, object, prim);
 }
 
 ccl_device_inline void kernel_embree_convert_hit(KernelGlobals kg,