Add alpha texture import

[seacat17]

Describe the project you are working on

A 3D demo.

Describe the problem or limitation you are having in your project

I have downloaded multiple CC0 models and textures and they all make a material that can be used in the project. The problem is that the alpha textures are stored separately sometimes and this creates a problem - there's nowhere I can import alpha textures in.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

It's simple. There should be an option to import the texture that will be used as an alpha channel, like this one.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

I import the diffuse texture, I switch the material transparency mode to anything related with Alpha and the engine displays a checkbox that says "External alpha texture". When this checkbox is checked, the engine gives me an ability to import the external alpha texture that it will apply to the diffuse texture.

If this enhancement will not be used often, can it be worked around with a few lines of script?

No.

Is there a reason why this should be core and not an add-on in the asset library?

Many CC0 materials and models come with textures that do not have an alpha channel so instead the alpha texture is stored separately. It is rather tedious to apply everything manually in GIMP.

EDIT: To make it worse, GIMP doesn't even have the feature that is needed to properly apply alpha textures, so it's up to you guys to fix this problem.