Cycles code internals: add support for mesh voxel grid attributes.

These are internally stored as a 3D image textures, but accessible like e.g.
UV coordinates though the attribute node and getattribute().

This is convenient for rendering e.g. smoke objects where data like density is
really a property of the mesh, and it avoids having to specify the smoke object
in a texture node, instead the material will work with any smoke domain.

intern/cycles/render/attribute.h

@@ -27,12 +27,20 @@
 CCL_NAMESPACE_BEGIN
 
 class Attribute;
-class AttributeSet;
 class AttributeRequest;
 class AttributeRequestSet;
+class AttributeSet;
+class ImageManager;
 class Mesh;
 struct Transform;
 
+/* Attributes for voxels are images */
+
+struct VoxelAttribute {
+	ImageManager *manager;
+	int slot;
+};
+
 /* Attribute
  *
  * Arbitrary data layers on meshes.
@@ -48,6 +56,7 @@ public:
 	AttributeElement element;
 
 	Attribute() {}
+	~Attribute();
 	void set(ustring name, TypeDesc type, AttributeElement element);
 	void reserve(int numverts, int numfaces, int numsteps, int numcurves, int numkeys, bool resize);
 
@@ -60,19 +69,23 @@ public:
 	float4 *data_float4() { return (float4*)data(); }
 	float *data_float() { return (float*)data(); }
 	Transform *data_transform() { return (Transform*)data(); }
+	VoxelAttribute *data_voxel()  { return ( VoxelAttribute*)data(); }
 
 	const char *data() const { return (buffer.size())? &buffer[0]: NULL; }
 	const float3 *data_float3() const { return (const float3*)data(); }
 	const float4 *data_float4() const { return (const float4*)data(); }
 	const float *data_float() const { return (const float*)data(); }
 	const Transform *data_transform() const { return (const Transform*)data(); }
+	const VoxelAttribute *data_voxel() const { return (const VoxelAttribute*)data(); }
 
 	void add(const float& f);
 	void add(const float3& f);
 	void add(const Transform& f);
+	void add(const VoxelAttribute& f);
 
 	static bool same_storage(TypeDesc a, TypeDesc b);
 	static const char *standard_name(AttributeStandard std);
+	static AttributeStandard name_standard(const char *name);
 };
 
 /* Attribute Set