Fix T87194: custom attributes not accessible with Cycles Volume

Custom properties defined on objects are not accessible from the
attribute node when rendering a volume in Cycles. This is because
this case is not handled.

To handle it, added a primitive type for volumes in the kernel,
which is then used in the initialization of ShaderData and to
check whether an attribute lookup is for a volume.

`volume_attribute_float4` is also now checking the attribute
element type to dispatch to the right lookup function.

Reviewed By: #cycles, brecht

Maniphest Tasks: T87194

Differential Revision: https://developer.blender.org/D11728

intern/cycles/kernel/geom/geom_primitive.h

@@ -138,7 +138,7 @@ ccl_device_inline float4 primitive_surface_attribute_float4(KernelGlobals *kg,
 ccl_device_inline bool primitive_is_volume_attribute(const ShaderData *sd,
                                                      const AttributeDescriptor desc)
 {
-  return (sd->object != OBJECT_NONE && desc.element == ATTR_ELEMENT_VOXEL);
+  return sd->type == PRIMITIVE_VOLUME;
 }
 
 ccl_device_inline float primitive_volume_attribute_float(KernelGlobals *kg,

intern/cycles/kernel/geom/geom_volume.h

@@ -72,14 +72,22 @@ ccl_device float4 volume_attribute_float4(KernelGlobals *kg,
                                           const ShaderData *sd,
                                           const AttributeDescriptor desc)
 {
-  /* todo: optimize this so we don't have to transform both here and in
-   * kernel_tex_image_interp_3d when possible. Also could optimize for the
-   * common case where transform is translation/scale only. */
-  float3 P = sd->P;
-  object_inverse_position_transform(kg, sd, &P);
-  InterpolationType interp = (sd->flag & SD_VOLUME_CUBIC) ? INTERPOLATION_CUBIC :
-                                                            INTERPOLATION_NONE;
-  return kernel_tex_image_interp_3d(kg, desc.offset, P, interp);
+  if (desc.element & (ATTR_ELEMENT_OBJECT | ATTR_ELEMENT_MESH)) {
+    return kernel_tex_fetch(__attributes_float3, desc.offset);
+  }
+  else if (desc.element == ATTR_ELEMENT_VOXEL) {
+    /* todo: optimize this so we don't have to transform both here and in
+     * kernel_tex_image_interp_3d when possible. Also could optimize for the
+     * common case where transform is translation/scale only. */
+    float3 P = sd->P;
+    object_inverse_position_transform(kg, sd, &P);
+    InterpolationType interp = (sd->flag & SD_VOLUME_CUBIC) ? INTERPOLATION_CUBIC :
+                                                              INTERPOLATION_NONE;
+    return kernel_tex_image_interp_3d(kg, desc.offset, P, interp);
+  }
+  else {
+    return make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+  }
 }
 
 #endif

intern/cycles/kernel/kernel_shader.h

@@ -1268,6 +1268,7 @@ ccl_device_inline void shader_eval_volume(KernelGlobals *kg,
   sd->num_closure_left = max_closures;
   sd->flag = 0;
   sd->object_flag = 0;
+  sd->type = PRIMITIVE_VOLUME;
 
   for (int i = 0; stack[i].shader != SHADER_NONE; i++) {
     /* setup shaderdata from stack. it's mostly setup already in

intern/cycles/kernel/kernel_types.h

@@ -694,17 +694,20 @@ typedef enum PrimitiveType {
    */
   PRIMITIVE_LAMP = (1 << 6),
 
+  PRIMITIVE_VOLUME = (1 << 7),
+
   PRIMITIVE_ALL_TRIANGLE = (PRIMITIVE_TRIANGLE | PRIMITIVE_MOTION_TRIANGLE),
   PRIMITIVE_ALL_CURVE = (PRIMITIVE_CURVE_THICK | PRIMITIVE_MOTION_CURVE_THICK |
                          PRIMITIVE_CURVE_RIBBON | PRIMITIVE_MOTION_CURVE_RIBBON),
+  PRIMITIVE_ALL_VOLUME = (PRIMITIVE_VOLUME),
   PRIMITIVE_ALL_MOTION = (PRIMITIVE_MOTION_TRIANGLE | PRIMITIVE_MOTION_CURVE_THICK |
                           PRIMITIVE_MOTION_CURVE_RIBBON),
-  PRIMITIVE_ALL = (PRIMITIVE_ALL_TRIANGLE | PRIMITIVE_ALL_CURVE),
+  PRIMITIVE_ALL = (PRIMITIVE_ALL_TRIANGLE | PRIMITIVE_ALL_CURVE | PRIMITIVE_ALL_VOLUME),
 
   /* Total number of different traceable primitives.
    * NOTE: This is an actual value, not a bitflag.
    */
-  PRIMITIVE_NUM_TOTAL = 6,
+  PRIMITIVE_NUM_TOTAL = 7,
 } PrimitiveType;
 
 #define PRIMITIVE_PACK_SEGMENT(type, segment) ((segment << PRIMITIVE_NUM_TOTAL) | (type))