Many thanks to the original Author of this patch: Christian Aguilera
The COLLADA importer was silently ignoring the alpha component in the
vertex data.
The `stride` variable holds the component count (3 for RGB; 4 for RGBA),
and can be used for honouring the alpha channel in the vertex data.
Test plan:
- Open Blender.
- Clear the scene.
- Add a plane.
- Enter **Vertex Paint** mode.
- Switch to the **Erase Alpha** blending mode.
- Select a tone of gray.
- Turn strength down to less than 1
- Paint [some of] the vertices of the plane.
- Export project as a COLLADA file (`.dae`).
- Clear the scene.
- Re-import the COLLADA file again.
- Export the project again (with different name).
**Without** this patch, the second exported project will have lost the
alpha component in their vertex data:
```lang=xml, counterexample
<float_array id="Plane-mesh-colors-Col-array" count="24">1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1</float_array>
```
**With** the patch, the first and the second exported projects retain
the alpha values painted previously:
```lang=xml
<float_array id="Plane-mesh-colors-Col-array" count="24">1 1 1 1 1 1 1 0.5490196 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0.5490196</float_array>
```
Reviewed By: cristian64, SonnyCampbell_Unity
Authored by: Christian Aguilera
Differential Revision: https://developer.blender.org/D14246
106d937a4e