Don't render decals on solid objects' backfaces

- Fixes issue with decals appearing on backfaces of transparent, solid objects.

Author: deranen

src/ccycles/ccycles.h

@@ -248,6 +248,11 @@ CCL_CAPI void CDECL cycles_scene_object_set_shader(ccl::Session* session_id, ccl
  * \ingroup ccycles_object
  */
 CCL_CAPI void CDECL cycles_scene_object_set_is_shadowcatcher(ccl::Session* session_id, ccl::Object*, bool is_shadowcatcher);
+/**
+ * Set is_solid flag for object
+ * \ingroup ccycles_object
+ */
+CCL_CAPI void CDECL cycles_scene_object_set_is_solid(ccl::Session* session_id, ccl::Object*, bool is_solid);
 /**
  * Set mesh_light_no_cast_shadow flag for object. This is to signal that this mesh light shouldn't cast shadows.
  * \ingroup ccycles_object

src/ccycles/object.cpp

@@ -148,6 +148,18 @@ void cycles_scene_object_set_is_shadowcatcher(ccl::Session* session_id, ccl::Obj
 	}
 }
 
+void cycles_scene_object_set_is_solid(ccl::Session* session_id, ccl::Object* object, bool is_solid)
+{
+	ASSERT(object);
+
+	ccl::Scene* sce = nullptr;
+	if(scene_find(session_id, &sce)) {
+		object->set_is_solid(is_solid);
+		object->tag_update(sce);
+		sce->light_manager->tag_update(sce, ccl::LightManager::UPDATE_ALL);
+	}
+}
+
 void cycles_scene_object_set_mesh_light_no_cast_shadow(ccl::Session* session_id, ccl::Object* object, bool mesh_light_no_cast_shadow)
 {
 	ASSERT(object);

src/kernel/svm/tex_coord.h

@@ -350,6 +350,8 @@ ccl_device_inline void decal_data_read(KernelGlobals kg,
   uint decal_map_side;
   uint type = node.y;
   uint out_offset = node.z;
+  const bool suppress_for_solid_backface =
+      ((sd->object_flag & SD_OBJECT_IS_SOLID) != 0) && ((sd->flag & SD_BACKFACING) != 0);
 
   float3 uv = stack_load_float3(stack, out_offset);
 
@@ -411,6 +413,7 @@ ccl_device_inline void decal_data_read(KernelGlobals kg,
     decal->cur_uv.x = uv.x;
     decal->cur_uv.y = uv.y;
     decal->data = map_to_uv(data, *decal);
+    decal->on_correct_side = !suppress_for_solid_backface;
   }
   else {
 
@@ -449,6 +452,10 @@ ccl_device_inline void decal_data_read(KernelGlobals kg,
         } break;
       }
     }
+
+    if (suppress_for_solid_backface) {
+      decal->on_correct_side = false;
+    }
   }
 
   // stack_store_float(stack, decal_forward_offset, dotp > 0.0f ? 1.0f : -1.0f);
@@ -696,7 +703,9 @@ ccl_device_noinline int svm_rhino_node_tex_coord(KernelGlobals kg,
       DecalData decal;
       decal_data_read(kg, sd, stack, node, &offset, &decal, 0);
       data = decal.data;
-      // data = map_to_uv(data, decal);
+      if (!decal.on_correct_side) {
+        data.z = -1.0f;
+      }
       break;
     }
     case NODE_TEXCO_ENV_DECAL_PLANAR: {
@@ -888,7 +897,9 @@ ccl_device_noinline int svm_node_tex_coord_bump_dx(KernelGlobals kg,
       DecalData decal;
       decal_data_read(kg, sd, stack, node, &offset, &decal, 0);
       data = decal.data;
-      // data = map_to_uv(data, decal);
+      if (!decal.on_correct_side) {
+        data.z = -1.0f;
+      }
       break;
     }
     case NODE_TEXCO_ENV_DECAL_PLANAR: {
@@ -1083,7 +1094,9 @@ ccl_device_noinline int svm_node_tex_coord_bump_dy(KernelGlobals kg,
       DecalData decal;
       decal_data_read(kg, sd, stack, node, &offset, &decal, 0);
       data = decal.data;
-      // data = map_to_uv(data, decal);
+      if (!decal.on_correct_side) {
+        data.z = -1.0f;
+      }
       break;
     }
     case NODE_TEXCO_ENV_DECAL_PLANAR: {

src/kernel/types.h

@@ -874,6 +874,8 @@ enum ShaderDataObjectFlag {
   SD_OBJECT_HAS_VOLUME_MOTION = (1 << 11),
   /* object is mesh lamp, but doesn't cast shadows */
   SD_OBJECT_LIGHT_NO_CAST_SHADOWS = (1 << 12),
+  /* object represents solid geometry */
+  SD_OBJECT_IS_SOLID = (1 << 13),
 
   /* object is using caustics */
   SD_OBJECT_CAUSTICS = (SD_OBJECT_CAUSTICS_CASTER | SD_OBJECT_CAUSTICS_RECEIVER),
@@ -882,7 +884,7 @@ enum ShaderDataObjectFlag {
                      SD_OBJECT_NEGATIVE_SCALE | SD_OBJECT_HAS_VOLUME |
                      SD_OBJECT_INTERSECTS_VOLUME | SD_OBJECT_SHADOW_CATCHER |
                      SD_OBJECT_HAS_VOLUME_ATTRIBUTES | SD_OBJECT_CAUSTICS |
-                     SD_OBJECT_HAS_VOLUME_MOTION)
+                     SD_OBJECT_HAS_VOLUME_MOTION | SD_OBJECT_IS_SOLID)
 };
 
 typedef struct ccl_align(16) ShaderData

src/scene/object.cpp

@@ -90,6 +90,7 @@ NODE_DEFINE(Object)
   SOCKET_STRING(asset_name, "Asset Name", ustring());
 
   SOCKET_BOOLEAN(is_shadow_catcher, "Shadow Catcher", false);
+  SOCKET_BOOLEAN(is_solid, "Solid", false);
   SOCKET_BOOLEAN(mesh_light_no_cast_shadow, "Mesh Light No Cast Shadow", false);
 
   SOCKET_BOOLEAN(is_caustics_caster, "Cast Shadow Caustics", false);
@@ -569,6 +570,9 @@ void ObjectManager::device_update_object_transform(UpdateObjectTransformState *s
   if (ob->use_holdout) {
     flag |= SD_OBJECT_HOLDOUT_MASK;
   }
+  if (ob->is_solid) {
+    flag |= SD_OBJECT_IS_SOLID;
+  }
   state->object_flag[ob->index] = flag;
   state->object_volume_step[ob->index] = FLT_MAX;
 

src/scene/object.h

@@ -53,6 +53,7 @@ class Object : public Node {
   NODE_SOCKET_API(bool, hide_on_missing_motion)
   NODE_SOCKET_API(bool, use_holdout)
   NODE_SOCKET_API(bool, is_shadow_catcher)
+  NODE_SOCKET_API(bool, is_solid)
   NODE_SOCKET_API(bool, mesh_light_no_cast_shadow)
   NODE_SOCKET_API(float, shadow_terminator_shading_offset)
   NODE_SOCKET_API(float, shadow_terminator_geometry_offset)