Export: Alpha values are ignored when sourcefile has no transparency

[emkajeej]

Describe the bug When connecting the color socket of an image that does not have an alpha channel to the alpha socket of the Principled BSDF, Blender correctly interprets black pixels als 0 alpha. When exported to a GLB, the tranparent pixels turn black.

This does not happen in Blender 4.0.

To Reproduce Steps to reproduce the behavior:

1. Add a plane
2. Add a new material
3. Import a black and white image and connect the Color to the Alpha
4. Export as GLB/GLTF
5. Open in any GLB viewer, like https://gltf.report/

Expected behavior The black and white values of the image are interpreted as alpha values, allowing for more granular control of the material's transparency.

Screenshots

Here is the same file exported from 4.0:

.blend file/ .gltf (mandatory) alphamap.blend.zip

Version

• OS: macOS 14.5
• Blender Version 4.1.1.

Additional context Issue does not occur in v < 4.1.