When allocating new `CustomData` layers, often we do redundant
initialization of arrays. For example, it's common that values are
allocated, set to their default value, and then set to some other
value. This is wasteful, and it negates the benefits of optimizations
to the allocator like D15082. There are two reasons for this. The
first is array-of-structs storage that makes it annoying to initialize
values manually, and the second is confusing options in the Custom Data
API. This patch addresses the latter.
The `CustomData` "alloc type" options are rearranged. Now, besides
the options that use existing layers, there are two remaining:
* `CD_SET_DEFAULT` sets the default value.
* Usually zeroes, but for colors this is white (how it was before).
* Should be used when you add the layer but don't set all values.
* `CD_CONSTRUCT` refers to the "default construct" C++ term.
* Only necessary or defined for non-trivial types like vertex groups.
* Doesn't do anything for trivial types like `int` or `float3`.
* Should be used every other time, when all values will be set.
The attribute API's `AttributeInit` types are updated as well.
To update code, replace `CD_CALLOC` with `CD_SET_DEFAULT` and
`CD_DEFAULT` with `CD_CONSTRUCT`. This doesn't cause any functional
changes yet. Follow-up commits will change to avoid initializing
new layers where the correctness is clear.
Differential Revision: https://developer.blender.org/D15617
The specific functions for vertex colors and and sculpt vertex colors
can be replaced by more generic attribute functions internally.
Also remove a paramter from one function.
The "Color Attributes" system from f7bbc7cdbb has replaced
both "Sculpt Vertex Colors" and "Vertex Colors" in the UI. The Operators
for adding and removing them are unused now.
This commit does not break backwards compatibility with the Python
API, it only removes the operators, which generally aren't used by
addons anyway. The mesh RNA properties will be removed in 4.0 (T100153).
Differential Revision: https://developer.blender.org/D15077
