After doing some tests on the 4.0 Beta we still can't reach a specific Emissive/Additive effect.

We have a creature with different variations using the same rig animation (example a run cycle). The creature is composed of different body parts (example: a normal leg with multiple bones and a spiky version of the same leg) which we group together under the same slot and activate only the images versions we want visible when animating. Until here, all goes well. But, we can't find a way to apply an emissive effect on top of one of the existing base colour for a leg (example : optional dots we want to glow in the dark over the base colour skin). We would need a way to be able to set an additive mode on just the emissive effect (as an unlite material) while having the base colour of the leg active (as a lite material) at the same time.

How would you reach that target? Would it be possible to assign an additive to an individual images/mesh with in a slot instead of on the entire slot itself?
Thanks a lot of any tips!

The Sprite shaders offer an Emissive texture slot which can be used, you can see it in action at the Stretchyman skeleton in the Sprite Shaders example scene, and in multiple URP scenes that also use this asset.

The alternative would be to just have a separate slot with additive blend mode set in Spine.

Theoretically you could also manually edit the alpha channel of the PMA atlas texture after it has been exported, using your favourite image editor. Then change the alpha value of the emissive pixels to 0 to change it to an additive effect on the texture side. You just need to be sure that your image editor is not messing with the RGB values when you set alpha to 0, which e.g. Photoshop does in some versions when exporting as png. If that's a problem, just save it as .tga or any other format that preserves the RGB information. Note that this is not a recommended workflow, as you will need to reapply your work when re-exporting your skeleton.

Thank you so much Harald, it works well with the Sprite Shader!

Glad to hear, thanks for getting back to us!