Cycles: Add support for native OptiX curve primitive

This patch adds support for the curve primitive from OptiX to Cycles. It's currently hidden
behind a debug option, since there can be some slight rendering differences still (because no
backface culling is performed and something seems off with endcaps). The curve primitive
was added with the OptiX 7.1 SDK and requires a r450 driver or newer, so this also updates
the codebase to be able to build with the new SDK.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D8223

1 files changed, 31 insertions, 17 deletions

diff --git a/intern/cycles/kernel/kernels/optix/kernel_optix.cu b/intern/cycles/kernel/kernels/optix/kernel_optix.cu
index c730d952ed4..3b166e59dfd 100644
--- a/intern/cycles/kernel/kernels/optix/kernel_optix.cu
+++ b/intern/cycles/kernel/kernels/optix/kernel_optix.cu
@@ -15,6 +15,7 @@
  * limitations under the License.
  */
 
+// clang-format off
 #include "kernel/kernel_compat_optix.h"
 #include "util/util_atomic.h"
 #include "kernel/kernel_types.h"
@@ -23,6 +24,7 @@
 
 #include "kernel/kernel_path.h"
 #include "kernel/kernel_bake.h"
+// clang-format on
 
 template<typename T> ccl_device_forceinline T *get_payload_ptr_0()
 {
@@ -139,8 +141,8 @@ extern "C" __global__ void __anyhit__kernel_optix_local_hit()
   }
   else {
     if (local_isect->num_hits && optixGetRayTmax() > local_isect->hits[0].t) {
-      // Record closest intersection only (do not terminate ray here, since there is no guarantee
-      // about distance ordering in anyhit)
+      // Record closest intersection only
+      // Do not terminate ray here, since there is no guarantee about distance ordering in any-hit
       return optixIgnoreIntersection();
     }
 
@@ -153,15 +155,9 @@ extern "C" __global__ void __anyhit__kernel_optix_local_hit()
   isect->object = get_object_id();
   isect->type = kernel_tex_fetch(__prim_type, isect->prim);
 
-  if (optixIsTriangleHit()) {
-    const float2 barycentrics = optixGetTriangleBarycentrics();
-    isect->u = 1.0f - barycentrics.y - barycentrics.x;
-    isect->v = barycentrics.x;
-  }
-  else {
-    isect->u = __uint_as_float(optixGetAttribute_0());
-    isect->v = __uint_as_float(optixGetAttribute_1());
-  }
+  const float2 barycentrics = optixGetTriangleBarycentrics();
+  isect->u = 1.0f - barycentrics.y - barycentrics.x;
+  isect->v = barycentrics.x;
 
   // Record geometric normal
   const uint tri_vindex = kernel_tex_fetch(__prim_tri_index, isect->prim);
@@ -198,10 +194,18 @@ extern "C" __global__ void __anyhit__kernel_optix_shadow_all_hit()
     isect->u = 1.0f - barycentrics.y - barycentrics.x;
     isect->v = barycentrics.x;
   }
+#  ifdef __HAIR__
   else {
-    isect->u = __uint_as_float(optixGetAttribute_0());
+    const float u = __uint_as_float(optixGetAttribute_0());
+    isect->u = u;
     isect->v = __uint_as_float(optixGetAttribute_1());
+
+    // Filter out curve endcaps
+    if (u == 0.0f || u == 1.0f) {
+      return optixIgnoreIntersection();
+    }
   }
+#  endif
 
 #  ifdef __TRANSPARENT_SHADOWS__
   // Detect if this surface has a shader with transparent shadows
@@ -213,7 +217,6 @@ extern "C" __global__ void __anyhit__kernel_optix_shadow_all_hit()
 #  ifdef __TRANSPARENT_SHADOWS__
   }
 
-  // TODO(pmours): Do we need REQUIRE_UNIQUE_ANYHIT for this to work?
   optixSetPayload_2(optixGetPayload_2() + 1);  // num_hits++
 
   // Continue tracing
@@ -227,13 +230,25 @@ extern "C" __global__ void __anyhit__kernel_optix_visibility_test()
   uint visibility = optixGetPayload_4();
 #ifdef __VISIBILITY_FLAG__
   const uint prim = optixGetPrimitiveIndex();
-  if ((kernel_tex_fetch(__prim_visibility, prim) & visibility) == 0)
+  if ((kernel_tex_fetch(__prim_visibility, prim) & visibility) == 0) {
     return optixIgnoreIntersection();
+  }
+#endif
+
+#ifdef __HAIR__
+  if (!optixIsTriangleHit()) {
+    // Filter out curve endcaps
+    const float u = __uint_as_float(optixGetAttribute_0());
+    if (u == 0.0f || u == 1.0f) {
+      return optixIgnoreIntersection();
+    }
+  }
 #endif
 
   // Shadow ray early termination
-  if (visibility & PATH_RAY_SHADOW_OPAQUE)
+  if (visibility & PATH_RAY_SHADOW_OPAQUE) {
     return optixTerminateRay();
+  }
 }
 
 extern "C" __global__ void __closesthit__kernel_optix_hit()
@@ -250,7 +265,7 @@ extern "C" __global__ void __closesthit__kernel_optix_hit()
     optixSetPayload_2(__float_as_uint(barycentrics.x));
   }
   else {
-    optixSetPayload_1(optixGetAttribute_0());
+    optixSetPayload_1(optixGetAttribute_0());  // Same as 'optixGetCurveParameter()'
     optixSetPayload_2(optixGetAttribute_1());
   }
 }
@@ -286,7 +301,6 @@ ccl_device_inline void optix_intersection_curve(const uint prim, const uint type
                             __float_as_int(isect.u),   // Attribute_0
                             __float_as_int(isect.v));  // Attribute_1
   }
-
 }
 
 extern "C" __global__ void __intersection__curve_ribbon()