In our brainstorming, we had the idea of a type of item dropped by enemies that will have a very particular look: it will reproduce bismuth and, in particular, its iridescence.

What is Iridescence?

Remember CD? The under side of CDs had some trippy colors that changed based on which angle you're looking at.

That type of effect is called iridescence.

Many other things has that kind of effect. Things like bubbles, some metals and even some bugs (especially beetles).

Wikipedia defines iridescence as:

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Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change colour as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, butterfly wings and seashells, as well as certain minerals. It is often created by structural coloration (microstructures that interfere with light).

In order to reproduce the visual qualities of bismuth, we must find how to recreate this effect in a shader.

One of my hypotheses is that we could do it with the normals and the viewing angle. I'm not an expert in shader writing but I'm sure that's possible ...