Alias incorrectly merges images with identical shape but different colors

[misaki-eymard]

Description:
Starting with Spine 4.2.38, when Alias is enabled in the Texture Packer settings, images that have the same shape (that is, identical pixel alpha) but different colors can be incorrectly merged. To reproduce this issue, it appears necessary to use images of the same shape that are either pure white or pure black.

In other words, the issue does not occur in the following case:

• A solid red image A and an orange image B that has the same shape as A

The issue does occur in the following cases:

• A solid red image A and a pure white image B with the same shape as A
• A solid red image A and a pure black image B with the same shape as A
• A pure white image A and a pure black image B with the same shape

Expected behavior:
Even if images share the same shape (identical pixel alpha), they should not be treated as the same image when their colors differ. Therefore, they should not be merged even when Alias is enabled.

Steps to reproduce:

1. Download the attached .zip file: 958-alias-issue.zip
2. Open the included Spine project file using Spine 4.3.39-beta.
3. Open the Export window, select either JSON or binary format, enable Pack, and export. The default Texture Packer settings are sufficient.
4. Check the generated texture. Although the skeleton contains both black and white squares, only the black square is packed.

The same behavior can also be observed by launching the Texture Packer separately and packing the images from the images folder. The images are merged in the same way.

Versions where this issue was observed:
4.2.38, 4.2.43, and 4.3.39-beta

This issue was reported via email.