GPU: Replace `GPUMaterialVolumeGrid` by `GPUMaterialAttribute`

This is to make the codegen and shading nodes object type agnostic. This
is essential for flexibility of the engine to use the nodetree as it see
fits.

The essential volume attributes struct properties are moved to the
`GPUMaterialAttribute` which see its final input name set on creation.

The binding process is centralized into `draw_volume.cc` to avoid
duplicating the code between multiple engines. It mimics the hair attributes
process.

Volume object grid transforms and other per object uniforms are packed into
one UBO per object. The grid transform is now based on object which simplify
the matrix preparations.

This also gets rid of the double transforms and use object info orco factors
for volume objects.

Tagging @brecht because he did the initial implementation of Volume Grids.

1 files changed, 17 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_common.h b/source/blender/draw/intern/draw_common.h
index 566e68a5c84..af2efd338e4 100644
--- a/source/blender/draw/intern/draw_common.h
+++ b/source/blender/draw/intern/draw_common.h
@@ -21,6 +21,7 @@ struct Object;
 struct ParticleSystem;
 struct RegionView3D;
 struct ViewLayer;
+struct Scene;
 struct DRWData;
 
 /* Keep in sync with globalsBlock in shaders */
@@ -74,6 +75,22 @@ void DRW_hair_init(void);
 void DRW_hair_update(void);
 void DRW_hair_free(void);
 
+/* draw_volume.cc */
+
+/**
+ * Add attributes bindings of volume grids to an exhisting shading group.
+ * No draw call is added so the caller can decide how to use the data.
+ * \return nullptr if there is something to draw.
+ */
+struct DRWShadingGroup *DRW_shgroup_volume_create_sub(struct Scene *scene,
+                                                      struct Object *ob,
+                                                      struct DRWShadingGroup *shgrp,
+                                                      struct GPUMaterial *gpu_material);
+
+void DRW_volume_init(struct DRWData *drw_data);
+void DRW_volume_ubos_pool_free(void *pool);
+void DRW_volume_free(void);
+
 /* draw_fluid.c */
 
 /* Fluid simulation. */