Fix "motion_blur" tests with OptiX in Cycles

Curves with motion blur produced wrong results with OptiX (T69801). This is because the AABBs for the motion steps were calculated from incorrect attribute data because the offset into the attribute data array was incorrect.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D5961

1 files changed, 8 insertions, 7 deletions

diff --git a/intern/cycles/device/device_optix.cpp b/intern/cycles/device/device_optix.cpp
index 84d7ecf6934..b745235aed5 100644
--- a/intern/cycles/device/device_optix.cpp
+++ b/intern/cycles/device/device_optix.cpp
@@ -881,20 +881,23 @@ class OptiXDevice : public Device {
 
         // Get AABBs for each motion step
         for (size_t step = 0; step < num_motion_steps; ++step) {
+          // The center step for motion vertices is not stored in the attribute
           const float3 *keys = mesh->curve_keys.data();
-
           size_t center_step = (num_motion_steps - 1) / 2;
-          // The center step for motion vertices is not stored in the attribute
           if (step != center_step) {
-            keys = motion_keys->data_float3() +
-                   (step > center_step ? step - 1 : step) * num_segments;
+            size_t attr_offset = (step > center_step) ? step - 1 : step;
+            // Technically this is a float4 array, but sizeof(float3) is the same as sizeof(float4)
+            keys = motion_keys->data_float3() + attr_offset * mesh->curve_keys.size();
           }
 
-          for (size_t i = step * num_segments, j = 0; j < num_curves; ++j) {
+          size_t i = step * num_segments;
+          for (size_t j = 0; j < num_curves; ++j) {
             const Mesh::Curve c = mesh->get_curve(j);
+
             for (size_t k = 0; k < c.num_segments(); ++i, ++k) {
               BoundBox bounds = BoundBox::empty;
               c.bounds_grow(k, keys, mesh->curve_radius.data(), bounds);
+
               aabb_data[i].minX = bounds.min.x;
               aabb_data[i].minY = bounds.min.y;
               aabb_data[i].minZ = bounds.min.z;
@@ -917,7 +920,6 @@ class OptiXDevice : public Device {
         // Disable visibility test anyhit program, since it is already checked during intersection
         // Those trace calls that require anyhit can force it with OPTIX_RAY_FLAG_ENFORCE_ANYHIT
         unsigned int build_flags = OPTIX_GEOMETRY_FLAG_DISABLE_ANYHIT;
-
         OptixBuildInput build_input = {};
         build_input.type = OPTIX_BUILD_INPUT_TYPE_CUSTOM_PRIMITIVES;
         build_input.aabbArray.aabbBuffers = (CUdeviceptr *)aabb_ptrs.data();
@@ -975,7 +977,6 @@ class OptiXDevice : public Device {
 
         // No special build flags for triangle primitives
         unsigned int build_flags = OPTIX_GEOMETRY_FLAG_NONE;
-
         OptixBuildInput build_input = {};
         build_input.type = OPTIX_BUILD_INPUT_TYPE_TRIANGLES;
         build_input.triangleArray.vertexBuffers = (CUdeviceptr *)vertex_ptrs.data();