Cycles: restore Denoising Depth pass, when enabling Denoising Data passes

This is still useful in some cases even if not used by OpenImageDenoise. In
the future this may be replaced with a more generic system to control render
passes and filtering, but for now this just does what it did before.

intern/cycles/blender/blender_sync.cpp

@@ -541,6 +541,7 @@ static PassType get_blender_pass_type(BL::RenderPass &b_pass)
 
   MAP_PASS("Denoising Normal", PASS_DENOISING_NORMAL);
   MAP_PASS("Denoising Albedo", PASS_DENOISING_ALBEDO);
+  MAP_PASS("Denoising Depth", PASS_DENOISING_DEPTH);
 
   MAP_PASS("Shadow Catcher", PASS_SHADOW_CATCHER);
   MAP_PASS("Noisy Shadow Catcher", PASS_SHADOW_CATCHER);
@@ -670,6 +671,9 @@ void BlenderSync::sync_render_passes(BL::RenderLayer &b_rlay, BL::ViewLayer &b_v
 
     b_engine.add_pass("Denoising Albedo", 3, "RGB", b_view_layer.name().c_str());
     pass_add(scene, PASS_DENOISING_ALBEDO, "Denoising Albedo", PassMode::NOISY);
+
+    b_engine.add_pass("Denoising Depth", 1, "Z", b_view_layer.name().c_str());
+    pass_add(scene, PASS_DENOISING_DEPTH, "Denoising Depth", PassMode::NOISY);
   }
 
   /* Custom AOV passes. */

intern/cycles/kernel/kernel_passes.h

@@ -52,6 +52,14 @@ ccl_device_forceinline void kernel_write_denoising_features_surface(
 
   ccl_global float *buffer = kernel_pass_pixel_render_buffer(kg, state, render_buffer);
 
+  if (kernel_data.film.pass_denoising_depth != PASS_UNUSED) {
+    const float3 denoising_feature_throughput = INTEGRATOR_STATE(
+        state, path, denoising_feature_throughput);
+    const float denoising_depth = ensure_finite(average(denoising_feature_throughput) *
+                                                sd->ray_length);
+    kernel_write_pass_float(buffer + kernel_data.film.pass_denoising_depth, denoising_depth);
+  }
+
   float3 normal = zero_float3();
   float3 diffuse_albedo = zero_float3();
   float3 specular_albedo = zero_float3();

intern/cycles/kernel/kernel_types.h

@@ -384,6 +384,7 @@ typedef enum PassType {
   PASS_MIST,
   PASS_DENOISING_NORMAL,
   PASS_DENOISING_ALBEDO,
+  PASS_DENOISING_DEPTH,
 
   /* PASS_SHADOW_CATCHER accumulates contribution of shadow catcher object which is not affected by
    * any other object. The pass accessor will divide the combined pass by the shadow catcher. The
@@ -1031,6 +1032,7 @@ typedef struct KernelFilm {
 
   int pass_denoising_normal;
   int pass_denoising_albedo;
+  int pass_denoising_depth;
 
   int pass_aov_color;
   int pass_aov_value;
@@ -1047,7 +1049,7 @@ typedef struct KernelFilm {
 
   int use_approximate_shadow_catcher;
 
-  int pad1, pad2, pad3;
+  int pad1, pad2;
 } KernelFilm;
 static_assert_align(KernelFilm, 16);
 

intern/cycles/render/film.cpp

@@ -339,6 +339,9 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
       case PASS_DENOISING_ALBEDO:
         kfilm->pass_denoising_albedo = kfilm->pass_stride;
         break;
+      case PASS_DENOISING_DEPTH:
+        kfilm->pass_denoising_depth = kfilm->pass_stride;
+        break;
 
       case PASS_SHADOW_CATCHER:
         kfilm->pass_shadow_catcher = kfilm->pass_stride;
@@ -665,7 +668,7 @@ uint Film::get_kernel_features(const Scene *scene) const
     const PassMode pass_mode = pass->get_mode();
 
     if (pass_mode == PassMode::DENOISED || pass_type == PASS_DENOISING_NORMAL ||
-        pass_type == PASS_DENOISING_ALBEDO) {
+        pass_type == PASS_DENOISING_ALBEDO || pass_type == PASS_DENOISING_DEPTH) {
       kernel_features |= KERNEL_FEATURE_DENOISING;
     }
 

intern/cycles/render/pass.cpp

@@ -100,6 +100,7 @@ const NodeEnum *Pass::get_type_enum()
     pass_type_enum.insert("mist", PASS_MIST);
     pass_type_enum.insert("denoising_normal", PASS_DENOISING_NORMAL);
     pass_type_enum.insert("denoising_albedo", PASS_DENOISING_ALBEDO);
+    pass_type_enum.insert("denoising_depth", PASS_DENOISING_DEPTH);
 
     pass_type_enum.insert("shadow_catcher", PASS_SHADOW_CATCHER);
     pass_type_enum.insert("shadow_catcher_sample_count", PASS_SHADOW_CATCHER_SAMPLE_COUNT);
@@ -294,6 +295,9 @@ PassInfo Pass::get_info(const PassType type, const bool include_albedo)
     case PASS_DENOISING_ALBEDO:
       pass_info.num_components = 3;
       break;
+    case PASS_DENOISING_DEPTH:
+      pass_info.num_components = 1;
+      break;
 
     case PASS_SHADOW_CATCHER:
       pass_info.num_components = 3;