FEAT: Texture channel packing for vertex colors

[KirilStrezikozin]

This bug report is:

• not a duplicate
• implemented/fixed

Describe the bug
Kas.st#8843 initially reported this on Discord. In short, when baking maps to vertex colors with a channel pack set up for these maps, the channel pack is not performed and only the first vertex color bake is saved, others are blank. Reason: channel packing was not implemented for maps baked to vertex colors.

To Reproduce
Steps to reproduce the behavior:

1. Add 2 maps (e.g. AO and Curvature).
2. Set bake to Vertex Colors.
3. Bake.
4. Only the first map is saved to a new vertex color layer, others are blank, and no channel pack.

Expected behavior
Channel packing for maps baked to vertex colors to work properly.

Screenshots

Desktop (please complete the following information):

• Any OS
• Blender 3.2 and higher
• BakeMaster 2.0 and higher

Additional context
@kas.st#8843 replied:

I thinking a good approach to fixing the issues are to 1. fix the overwriting of the first vertex attribute => all data is written to the channels, 2. post process packing: create new attribute and copy individual channels. (3. delete 'buffer attributes')

[KirilStrezikozin]

Todo:

• Fix vertex colors bakes are not written correctly. The first layer is overwritten, and others are not filled with data. The active layer should be set and selected.
• Fix vertex color layers are not created when running the next bake. Vertex color layers are interpreted as images. It is unlikely to be only connected with layer name duplicates. There was no functionality to determine the correct naming of the new vertex color layer, neither respecting the value of bm_props.global_use_bake_overwrite.

[KirilStrezikozin]

Since vertex color layers are now properly written and saved, the channel packing feature can be implemented for them.
Todo:

• Add channel packing feature for vertex colors. Mind the suggestion:

2. post process packing: create a new attribute and copy individual channels. (3. delete 'buffer attributes')

My integration would be:

1. Create a new attribute Select the 'holder' attribute (like it is done for the regular channel pack with images).
2. Write individual channels from layers from the channel pack into corresponding RGBA channels of the 'holder' layer.
3. Delete 'buffer attributes'.

• Edit Baked Material creation to support vertex color layers.