Add Chromium-only Blender WebEngine parity work

blender-5.2.0/intern/cycles/kernel/light/distribution.h

@@ -0,0 +1,60 @@
+/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
+ *
+ * SPDX-License-Identifier: Apache-2.0 */
+
+#pragma once
+
+#include "kernel/globals.h"
+
+#include "kernel/light/common.h"
+
+CCL_NAMESPACE_BEGIN
+
+/* Simple CDF based sampling over all lights in the scene, without taking into
+ * account shading position or normal. */
+
+ccl_device int light_distribution_sample(KernelGlobals kg, const float rand)
+{
+  /* This is basically std::upper_bound as used by PBRT, to find a point light or
+   * triangle to emit from, proportional to area. a good improvement would be to
+   * also sample proportional to power, though it's not so well defined with
+   * arbitrary shaders. */
+  int first = 0;
+  int len = kernel_data.integrator.num_distribution + 1;
+
+  do {
+    const int half_len = len >> 1;
+    const int middle = first + half_len;
+
+    if (rand < kernel_data_fetch(light_distribution, middle).totarea) {
+      len = half_len;
+    }
+    else {
+      first = middle + 1;
+      len = len - half_len - 1;
+    }
+  } while (len > 0);
+
+  /* Clamping should not be needed but float rounding errors seem to
+   * make this fail on rare occasions. */
+  const int index = clamp(first - 1, 0, kernel_data.integrator.num_distribution - 1);
+
+  return index;
+}
+
+ccl_device bool light_distribution_sample(KernelGlobals kg,
+                                          const float rand,
+                                          ccl_private LightSample *ls)
+{
+  /* Sample light index from distribution. */
+  ls->emitter_id = light_distribution_sample(kg, rand);
+  ls->pdf_selection = kernel_data.integrator.distribution_pdf_lights;
+  return true;
+}
+
+ccl_device_inline float light_distribution_pdf_lamp(KernelGlobals kg)
+{
+  return kernel_data.integrator.distribution_pdf_lights;
+}
+
+CCL_NAMESPACE_END