Fix T100537: wrong depth pass for background after recent fix for gaps

Also have to write if we hit the background and have not written any valid
value for the pass yet.

intern/cycles/kernel/film/data_passes.h

@@ -157,4 +157,47 @@ ccl_device_inline void film_write_data_passes(KernelGlobals kg,
 #endif
 }
 
+ccl_device_inline void film_write_data_passes_background(
+    KernelGlobals kg, IntegratorState state, ccl_global float *ccl_restrict render_buffer)
+{
+#ifdef __PASSES__
+  const uint32_t path_flag = INTEGRATOR_STATE(state, path, flag);
+
+  if (!(path_flag & PATH_RAY_TRANSPARENT_BACKGROUND)) {
+    return;
+  }
+
+  /* Don't write data passes for paths that were split off for shadow catchers
+   * to avoid double-counting. */
+  if (path_flag & PATH_RAY_SHADOW_CATCHER_PASS) {
+    return;
+  }
+
+  const int flag = kernel_data.film.pass_flag;
+
+  if (!(flag & PASS_ANY)) {
+    return;
+  }
+
+  if (!(path_flag & PATH_RAY_SINGLE_PASS_DONE)) {
+    ccl_global float *buffer = film_pass_pixel_render_buffer(kg, state, render_buffer);
+
+    if (INTEGRATOR_STATE(state, path, sample) == 0) {
+      if (flag & PASSMASK(DEPTH)) {
+        film_overwrite_pass_float(buffer + kernel_data.film.pass_depth, 0.0f);
+      }
+      if (flag & PASSMASK(OBJECT_ID)) {
+        film_overwrite_pass_float(buffer + kernel_data.film.pass_object_id, 0.0f);
+      }
+      if (flag & PASSMASK(MATERIAL_ID)) {
+        film_overwrite_pass_float(buffer + kernel_data.film.pass_material_id, 0.0f);
+      }
+      if (flag & PASSMASK(POSITION)) {
+        film_overwrite_pass_float3(buffer + kernel_data.film.pass_position, zero_float3());
+      }
+    }
+  }
+#endif
+}
+
 CCL_NAMESPACE_END

intern/cycles/kernel/integrator/shade_background.h

@@ -3,6 +3,7 @@
 
 #pragma once
 
+#include "kernel/film/data_passes.h"
 #include "kernel/film/light_passes.h"
 
 #include "kernel/integrator/guiding.h"
@@ -131,6 +132,7 @@ ccl_device_inline void integrate_background(KernelGlobals kg,
 
   /* Write to render buffer. */
   film_write_background(kg, state, L, transparent, is_transparent_background_ray, render_buffer);
+  film_write_data_passes_background(kg, state, render_buffer);
 }
 
 ccl_device_inline void integrate_distant_lights(KernelGlobals kg,