We're experimenting with lighting our spine assets using the Pixel Lit shader with Unity's built-in rendering pipeline, and we're wondering if there's something we can do about the black outlines around skeleton parts that show up when using spot/point lights.
In fact, we don't really understand why they're showing up in the first place. The phenomenon can be replicated with the sample spineboy asset. When lit with a directional light, it looks perfectly fine, but when spot/point light is affecting it, an outline can be seen around the mouth texture. We think this is some sort of depth texture-alpha cutoff issue, but the original texture as viewed in the Spine editor does not have such an outline (our own assets are the same—specifically drawn to not have outlines and instead fade out at overlapping areas). We can understand if the alpha cutoff removes a bit of the texture edge, but we don't understand why it would add a black outline when lit, and only with spot/point lights at that.
We'd appreciate if someone could explain the cause for the outlines, and more so if a potential solution could be offered. We have provided some screenshots to illustrate the issue.
Note: we are using linear color space and therefore exporting/importing straight alpha textures (with Bleed in spine editor).
Thank you in advance for your time!