Attribute Node: support accessing attributes of View Layer and Scene.

The attribute node already allows accessing attributes associated
with objects and meshes, which allows changing the behavior of the
same material between different objects or instances. The same idea
can be extended to an even more global level of layers and scenes.

Currently view layers provide an option to replace all materials
with a different one. However, since the same material will be applied
to all objects in the layer, varying the behavior between layers while
preserving distinct materials requires duplicating objects.

Providing access to properties of layers and scenes via the attribute
node enables making materials with built-in switches or settings that
can be controlled globally at the view layer level. This is probably
most useful for complex NPR shading and compositing. Like with objects,
the node can also access built-in scene properties, like render resolution
or FOV of the active camera. Lookup is also attempted in World, similar
to how the Object mode checks the Mesh datablock.

In Cycles this mode is implemented by replacing the attribute node with
the attribute value during sync, allowing constant folding to take the
values into account. This means however that materials that use this
feature have to be re-synced upon any changes to scene, world or camera.

The Eevee version uses a new uniform buffer containing a sorted array
mapping name hashes to values, with binary search lookup. The array
is limited to 512 entries, which is effectively limitless even
considering it is shared by all materials in the scene; it is also
just 16KB of memory so no point trying to optimize further.
The buffer has to be rebuilt when new attributes are detected in a
material, so the draw engine keeps a table of recently seen attribute
names to minimize the chance of extra rebuilds mid-draw.

Differential Revision: https://developer.blender.org/D15941

1 files changed, 9 insertions, 0 deletions

diff --git a/source/blender/gpu/intern/gpu_node_graph.h b/source/blender/gpu/intern/gpu_node_graph.h
index 7db22151f86..de0a0687b13 100644
--- a/source/blender/gpu/intern/gpu_node_graph.h
+++ b/source/blender/gpu/intern/gpu_node_graph.h
@@ -31,6 +31,7 @@ typedef enum eGPUDataSource {
   GPU_SOURCE_UNIFORM,
   GPU_SOURCE_ATTR,
   GPU_SOURCE_UNIFORM_ATTR,
+  GPU_SOURCE_LAYER_ATTR,
   GPU_SOURCE_STRUCT,
   GPU_SOURCE_TEX,
   GPU_SOURCE_TEX_TILED_MAPPING,
@@ -42,6 +43,7 @@ typedef enum {
   GPU_NODE_LINK_NONE = 0,
   GPU_NODE_LINK_ATTR,
   GPU_NODE_LINK_UNIFORM_ATTR,
+  GPU_NODE_LINK_LAYER_ATTR,
   GPU_NODE_LINK_COLORBAND,
   GPU_NODE_LINK_CONSTANT,
   GPU_NODE_LINK_IMAGE,
@@ -95,6 +97,8 @@ struct GPUNodeLink {
     struct GPUMaterialAttribute *attr;
     /* GPU_NODE_LINK_UNIFORM_ATTR */
     struct GPUUniformAttr *uniform_attr;
+    /* GPU_NODE_LINK_LAYER_ATTR */
+    struct GPULayerAttr *layer_attr;
     /* GPU_NODE_LINK_IMAGE_BLENDER */
     struct GPUMaterialTexture *texture;
     /* GPU_NODE_LINK_DIFFERENTIATE_FLOAT_FN */
@@ -131,6 +135,8 @@ typedef struct GPUInput {
     struct GPUMaterialAttribute *attr;
     /* GPU_SOURCE_UNIFORM_ATTR */
     struct GPUUniformAttr *uniform_attr;
+    /* GPU_SOURCE_LAYER_ATTR */
+    struct GPULayerAttr *layer_attr;
     /* GPU_SOURCE_FUNCTION_CALL */
     char function_call[64];
   };
@@ -171,6 +177,9 @@ typedef struct GPUNodeGraph {
   /* The list of uniform attributes. */
   GPUUniformAttrList uniform_attrs;
 
+  /* The list of layer attributes. */
+  ListBase layer_attrs;
+
   /** Set of all the GLSL lib code blocks . */
   GSet *used_libraries;
 } GPUNodeGraph;