sycl: hoist timeSegment computation in motion blur mesh paths

For motion-blur triangle and quad meshes, each vertex(i, time) call
independently recomputes timeSegment(time, ftime), which involves a
floating-point divide, multiply, floor, and clamp.  Since all vertices
of the same primitive are sampled at identical ray.time(), the segment
index and fractional time are the same for every vertex in the batch.

Compute timeSegment once per primitive and call the indexed
vertex(i, itime) overload with a manual lerp for all three (triangle)
or four (quad) vertices.  This eliminates 2-3 redundant timeSegment
computations per procedural motion-blur primitive hit.

Author: stefanatwork

kernels/sycl/rthwif_embree.cpp

@@ -384,9 +384,10 @@ __forceinline bool intersect_primitive(intel_ray_query_t& query, Ray& ray, Scene
   {
     const TriangleMesh* triangle_mesh = (const TriangleMesh*) geom;
     const TriangleMesh::Triangle triangle = triangle_mesh->triangle(primID);
-    Vec3fa v0 = triangle_mesh->vertex(triangle.v[0], ray.time());
-    Vec3fa v1 = triangle_mesh->vertex(triangle.v[1], ray.time());
-    Vec3fa v2 = triangle_mesh->vertex(triangle.v[2], ray.time());
+    float ftime; const size_t itime = triangle_mesh->timeSegment(ray.time(), ftime);
+    const Vec3fa v0 = lerp(triangle_mesh->vertex(triangle.v[0], itime+0), triangle_mesh->vertex(triangle.v[0], itime+1), ftime);
+    const Vec3fa v1 = lerp(triangle_mesh->vertex(triangle.v[1], itime+0), triangle_mesh->vertex(triangle.v[1], itime+1), ftime);
+    const Vec3fa v2 = lerp(triangle_mesh->vertex(triangle.v[2], itime+0), triangle_mesh->vertex(triangle.v[2], itime+1), ftime);
     return TriangleIntersector().intersect(ray,v0,v1,v2,Intersect1Epilog1_HWIF<Ray>(ray, context, geomID, primID, filter));
   } else
 #endif
@@ -396,10 +397,11 @@ __forceinline bool intersect_primitive(intel_ray_query_t& query, Ray& ray, Scene
   {
     const QuadMesh* quad_mesh = (const QuadMesh*) geom;
     const QuadMesh::Quad quad = quad_mesh->quad(primID);
-    Vec3fa v0 = quad_mesh->vertex(quad.v[0], ray.time());
-    Vec3fa v1 = quad_mesh->vertex(quad.v[1], ray.time());
-    Vec3fa v2 = quad_mesh->vertex(quad.v[2], ray.time());
-    Vec3fa v3 = quad_mesh->vertex(quad.v[3], ray.time());
+    float ftime; const size_t itime = quad_mesh->timeSegment(ray.time(), ftime);
+    const Vec3fa v0 = lerp(quad_mesh->vertex(quad.v[0], itime+0), quad_mesh->vertex(quad.v[0], itime+1), ftime);
+    const Vec3fa v1 = lerp(quad_mesh->vertex(quad.v[1], itime+0), quad_mesh->vertex(quad.v[1], itime+1), ftime);
+    const Vec3fa v2 = lerp(quad_mesh->vertex(quad.v[2], itime+0), quad_mesh->vertex(quad.v[2], itime+1), ftime);
+    const Vec3fa v3 = lerp(quad_mesh->vertex(quad.v[3], itime+0), quad_mesh->vertex(quad.v[3], itime+1), ftime);
     bool ishit0 = TriangleIntersector().intersect(ray,v0,v1,v3,Intersect1Epilog1_HWIF<Ray>(ray, context, geomID, primID, filter));
     bool ishit1 = TriangleIntersector().intersect(ray,v2,v3,v1,[&](float &u, float &v, Vec3f& Ng) { u = 1.f - u; v = 1.f - v; }, Intersect1Epilog1_HWIF<Ray>(ray, context, geomID, primID, filter));
     return ishit0 || ishit1;