Two materials in one object; panning the UVs of one affects the other.

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1

Godot Version

4.3 & 4.5.1

Question

Is this a bug or just me doing something wrong?

demo

In the GIF, the parameters affect both material slots, not only their own. This is what the shaders looks like:

shader
shader1152Ă—332 80.2 KB

Both are the same but with different texture and variable name. I got this on 4.3 but reproduced it on 4.5.1 as well. If I make the parameters be inside the material instead (by removing the instance qualifier) the problem is solved, but then all the objects look the same because the changes are on the material. If I fix that by making the material local to scene then I can change those objects individually, but I’m instancing hundreds of copies of the same material.

My objective is to be able to have hundreds of instances of the cylinder, all of different colors by panning UVs over a palette. I want the panning to be independent from other instances and also from other material slots, and ideally all with the same material to make it more efficient, hence the parameters on the instances. Is this a design limitation that I just don’t know about, or a bug, or something I’m doing wrong?

2

It’s mentioned in the restrictions paragraph on the docs page about per instance uniforms:

If your mesh uses multiple materials, the parameters for the first mesh material found will “win” over the subsequent ones, unless they have the same name, index and type. In this case, all parameters are affected correctly.

If you run into the above situation, you can avoid clashes by manually specifying the index (0-15) of the instance uniform by using the instance_index hint:

instance uniform vec4 my_color : source_color, instance_index(5);
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