Iridescent shader breakdown

I recently made an iridescent shader in Unity using shaderlab and hlsl. I decided to apply it to my illustration of the seven of swords tarot card. Here’s a breakdown of how I made it.

So from a quick wikipedia search I got a simple definition of irridescence.

That’s great because we can easily access the view angle and angle of illumination in a shader. Since I wasn’t going to be moving the camera, I decided to try just using the light direction and normal direction to decide the colour.

First I wanted to get the worldspace normal. We can do this easily in the vert shader using one of Unity’s built-in functions.

Then we can pass this to the frag shader. I used the dot product of the light direction and worldspace normal to achieve this shadow effect.

Next, I wanted to add colour that changes depending on the dot product result, for this I decided to use a gradient ramp texture. I mapped a gradient texture using the result of the dot product as the UV co-ordinates.

That gave me a nice gradient that moved depending on the light/ normal direction.

I tried out several gradients to see how they looked and settled on this gradient as I felt it gave me the effect I was going for.

I simply added this to the normalised worldspace normals.

Then, as before, I used the result as the UV co-ordinates for the ramp texture. That gave it this great warped effect.

As a final touch, to make it more like a sparkly collectable card, I also added a voronoi noise normal map on top of the perlin noise normal map and it looked like this:

Finally, to add it to the tarot card, I made a black and white mask texture and used that to ensure the effect only shows up on the swords.

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