Cycles: decouple shadow paths from main path on GPU

The motivation for this is twofold. It improves performance (5-10% on most
benchmark scenes), and will help  to bring back transparency support for the
ambient occlusion pass.

* Duplicate some members from the main path state in the shadow path state.
* Add shadow paths incrementally to the array similar to what we do for
  the shadow catchers.
* For the scheduling, allow running shade surface and shade volume kernels
  as long as there is enough space in the shadow paths array. If not, execute
  shadow kernels until it is empty.

* Add IntegratorShadowState and ConstIntegratorShadowState typedefs that
  can be different between CPU and GPU. For GPU both main and shadow paths
  juse have an integer for SoA access. Bt with CPU it's a different pointer
  type so we get type safety checks in code shared between CPU and GPU.
* For CPU, add a separate IntegratorShadowStateCPU struct embedded in
  IntegratorShadowState.
* Update various functions to take the shadow state, and make SVM take either
  type of state using templates.

Differential Revision: https://developer.blender.org/D12889

1 files changed, 7 insertions, 4 deletions

diff --git a/intern/cycles/kernel/integrator/integrator_megakernel.h b/intern/cycles/kernel/integrator/integrator_megakernel.h
index a3b2b1f9e90..6e3220aa3b7 100644
--- a/intern/cycles/kernel/integrator/integrator_megakernel.h
+++ b/intern/cycles/kernel/integrator/integrator_megakernel.h
@@ -39,14 +39,17 @@ ccl_device void integrator_megakernel(KernelGlobals kg,
    * TODO: investigate if we can use device side enqueue for GPUs to avoid
    * having to compile this big kernel. */
   while (true) {
-    if (INTEGRATOR_STATE(state, shadow_path, queued_kernel)) {
+    const uint32_t shadow_queued_kernel = INTEGRATOR_STATE(
+        &state->shadow, shadow_path, queued_kernel);
+
+    if (shadow_queued_kernel) {
       /* First handle any shadow paths before we potentially create more shadow paths. */
-      switch (INTEGRATOR_STATE(state, shadow_path, queued_kernel)) {
+      switch (shadow_queued_kernel) {
         case DEVICE_KERNEL_INTEGRATOR_INTERSECT_SHADOW:
-          integrator_intersect_shadow(kg, state);
+          integrator_intersect_shadow(kg, &state->shadow);
           break;
         case DEVICE_KERNEL_INTEGRATOR_SHADE_SHADOW:
-          integrator_shade_shadow(kg, state, render_buffer);
+          integrator_shade_shadow(kg, &state->shadow, render_buffer);
           break;
         default:
           kernel_assert(0);