Cycles: merge of cycles-x branch, a major update to the renderer

This includes much improved GPU rendering performance, viewport interactivity,
new shadow catcher, revamped sampling settings, subsurface scattering anisotropy,
new GPU volume sampling, improved PMJ sampling pattern, and more.

Some features have also been removed or changed, breaking backwards compatibility.
Including the removal of the OpenCL backend, for which alternatives are under
development.

Release notes and code docs:
https://wiki.blender.org/wiki/Reference/Release_Notes/3.0/Cycles
https://wiki.blender.org/wiki/Source/Render/Cycles

Credits:
* Sergey Sharybin
* Brecht Van Lommel
* Patrick Mours (OptiX backend)
* Christophe Hery (subsurface scattering anisotropy)
* William Leeson (PMJ sampling pattern)
* Alaska (various fixes and tweaks)
* Thomas Dinges (various fixes)

For the full commit history, see the cycles-x branch. This squashes together
all the changes since intermediate changes would often fail building or tests.

Ref T87839, T87837, T87836
Fixes T90734, T89353, T80267, T80267, T77185, T69800

1 files changed, 198 insertions, 0 deletions

diff --git a/intern/cycles/kernel/integrator/integrator_intersect_volume_stack.h b/intern/cycles/kernel/integrator/integrator_intersect_volume_stack.h
new file mode 100644
index 00000000000..60d8a8e3e54
--- /dev/null
+++ b/intern/cycles/kernel/integrator/integrator_intersect_volume_stack.h
@@ -0,0 +1,198 @@
+/*
+ * Copyright 2011-2021 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include "kernel/bvh/bvh.h"
+#include "kernel/geom/geom.h"
+#include "kernel/integrator/integrator_volume_stack.h"
+#include "kernel/kernel_shader.h"
+
+CCL_NAMESPACE_BEGIN
+
+ccl_device void integrator_volume_stack_update_for_subsurface(INTEGRATOR_STATE_ARGS,
+                                                              const float3 from_P,
+                                                              const float3 to_P)
+{
+  PROFILING_INIT(kg, PROFILING_INTERSECT_VOLUME_STACK);
+
+  ShaderDataTinyStorage stack_sd_storage;
+  ShaderData *stack_sd = AS_SHADER_DATA(&stack_sd_storage);
+
+  kernel_assert(kernel_data.integrator.use_volumes);
+
+  Ray volume_ray ccl_optional_struct_init;
+  volume_ray.P = from_P;
+  volume_ray.D = normalize_len(to_P - from_P, &volume_ray.t);
+
+#ifdef __VOLUME_RECORD_ALL__
+  Intersection hits[2 * VOLUME_STACK_SIZE + 1];
+  uint num_hits = scene_intersect_volume_all(
+      kg, &volume_ray, hits, 2 * VOLUME_STACK_SIZE, PATH_RAY_ALL_VISIBILITY);
+  if (num_hits > 0) {
+    Intersection *isect = hits;
+
+    qsort(hits, num_hits, sizeof(Intersection), intersections_compare);
+
+    for (uint hit = 0; hit < num_hits; ++hit, ++isect) {
+      shader_setup_from_ray(kg, stack_sd, &volume_ray, isect);
+      volume_stack_enter_exit(INTEGRATOR_STATE_PASS, stack_sd);
+    }
+  }
+#else
+  Intersection isect;
+  int step = 0;
+  while (step < 2 * VOLUME_STACK_SIZE &&
+         scene_intersect_volume(kg, &volume_ray, &isect, PATH_RAY_ALL_VISIBILITY)) {
+    shader_setup_from_ray(kg, stack_sd, &volume_ray, &isect);
+    volume_stack_enter_exit(INTEGRATOR_STATE_PASS, stack_sd);
+
+    /* Move ray forward. */
+    volume_ray.P = ray_offset(stack_sd->P, -stack_sd->Ng);
+    if (volume_ray.t != FLT_MAX) {
+      volume_ray.D = normalize_len(to_P - volume_ray.P, &volume_ray.t);
+    }
+    ++step;
+  }
+#endif
+}
+
+ccl_device void integrator_intersect_volume_stack(INTEGRATOR_STATE_ARGS)
+{
+  PROFILING_INIT(kg, PROFILING_INTERSECT_VOLUME_STACK);
+
+  ShaderDataTinyStorage stack_sd_storage;
+  ShaderData *stack_sd = AS_SHADER_DATA(&stack_sd_storage);
+
+  Ray volume_ray ccl_optional_struct_init;
+  integrator_state_read_ray(INTEGRATOR_STATE_PASS, &volume_ray);
+  volume_ray.t = FLT_MAX;
+
+  const uint visibility = (INTEGRATOR_STATE(path, flag) & PATH_RAY_ALL_VISIBILITY);
+  int stack_index = 0, enclosed_index = 0;
+
+  /* Write background shader. */
+  if (kernel_data.background.volume_shader != SHADER_NONE) {
+    const VolumeStack new_entry = {OBJECT_NONE, kernel_data.background.volume_shader};
+    integrator_state_write_volume_stack(INTEGRATOR_STATE_PASS, stack_index, new_entry);
+    stack_index++;
+  }
+
+#ifdef __VOLUME_RECORD_ALL__
+  Intersection hits[2 * VOLUME_STACK_SIZE + 1];
+  uint num_hits = scene_intersect_volume_all(
+      kg, &volume_ray, hits, 2 * VOLUME_STACK_SIZE, visibility);
+  if (num_hits > 0) {
+    int enclosed_volumes[VOLUME_STACK_SIZE];
+    Intersection *isect = hits;
+
+    qsort(hits, num_hits, sizeof(Intersection), intersections_compare);
+
+    for (uint hit = 0; hit < num_hits; ++hit, ++isect) {
+      shader_setup_from_ray(kg, stack_sd, &volume_ray, isect);
+      if (stack_sd->flag & SD_BACKFACING) {
+        bool need_add = true;
+        for (int i = 0; i < enclosed_index && need_add; ++i) {
+          /* If ray exited the volume and never entered to that volume
+           * it means that camera is inside such a volume.
+           */
+          if (enclosed_volumes[i] == stack_sd->object) {
+            need_add = false;
+          }
+        }
+        for (int i = 0; i < stack_index && need_add; ++i) {
+          /* Don't add intersections twice. */
+          VolumeStack entry = integrator_state_read_volume_stack(INTEGRATOR_STATE_PASS, i);
+          if (entry.object == stack_sd->object) {
+            need_add = false;
+            break;
+          }
+        }
+        if (need_add && stack_index < VOLUME_STACK_SIZE - 1) {
+          const VolumeStack new_entry = {stack_sd->object, stack_sd->shader};
+          integrator_state_write_volume_stack(INTEGRATOR_STATE_PASS, stack_index, new_entry);
+          ++stack_index;
+        }
+      }
+      else {
+        /* If ray from camera enters the volume, this volume shouldn't
+         * be added to the stack on exit.
+         */
+        enclosed_volumes[enclosed_index++] = stack_sd->object;
+      }
+    }
+  }
+#else
+  int enclosed_volumes[VOLUME_STACK_SIZE];
+  int step = 0;
+
+  while (stack_index < VOLUME_STACK_SIZE - 1 && enclosed_index < VOLUME_STACK_SIZE - 1 &&
+         step < 2 * VOLUME_STACK_SIZE) {
+    Intersection isect;
+    if (!scene_intersect_volume(kg, &volume_ray, &isect, visibility)) {
+      break;
+    }
+
+    shader_setup_from_ray(kg, stack_sd, &volume_ray, &isect);
+    if (stack_sd->flag & SD_BACKFACING) {
+      /* If ray exited the volume and never entered to that volume
+       * it means that camera is inside such a volume.
+       */
+      bool need_add = true;
+      for (int i = 0; i < enclosed_index && need_add; ++i) {
+        /* If ray exited the volume and never entered to that volume
+         * it means that camera is inside such a volume.
+         */
+        if (enclosed_volumes[i] == stack_sd->object) {
+          need_add = false;
+        }
+      }
+      for (int i = 0; i < stack_index && need_add; ++i) {
+        /* Don't add intersections twice. */
+        VolumeStack entry = integrator_state_read_volume_stack(INTEGRATOR_STATE_PASS, i);
+        if (entry.object == stack_sd->object) {
+          need_add = false;
+          break;
+        }
+      }
+      if (need_add) {
+        const VolumeStack new_entry = {stack_sd->object, stack_sd->shader};
+        integrator_state_write_volume_stack(INTEGRATOR_STATE_PASS, stack_index, new_entry);
+        ++stack_index;
+      }
+    }
+    else {
+      /* If ray from camera enters the volume, this volume shouldn't
+       * be added to the stack on exit.
+       */
+      enclosed_volumes[enclosed_index++] = stack_sd->object;
+    }
+
+    /* Move ray forward. */
+    volume_ray.P = ray_offset(stack_sd->P, -stack_sd->Ng);
+    ++step;
+  }
+#endif
+
+  /* Write terminator. */
+  const VolumeStack new_entry = {OBJECT_NONE, SHADER_NONE};
+  integrator_state_write_volume_stack(INTEGRATOR_STATE_PASS, stack_index, new_entry);
+
+  INTEGRATOR_PATH_NEXT(DEVICE_KERNEL_INTEGRATOR_INTERSECT_VOLUME_STACK,
+                       DEVICE_KERNEL_INTEGRATOR_INTERSECT_CLOSEST);
+}
+
+CCL_NAMESPACE_END