Remapping colours on textures dynamically in unity

Question

I'm making a RTS game in Unity. In such games, players usually can determine the unit allegiance using the unit color markings. And I'm now trying to implement system, that will remap purple color on the unit owner's color.

One idea was to determine color that will be used as mask and then recoloured to any color. It could be done using some hue distribution function:

Solution 1

I used funtion based on max(). You can see the plot there.

hue = min(hue, pow(Math.abs(hue-MASK_HUE),8)*5000000+RESULT_HUE)

This solution has two big flaws:

1. Purple can't be used (I don't like it anyway)
2. Only full colours are applicable (no brown, black, white...)

^{What you see above is just my fiddling. The actual project would run on Unity engine in C#.}

Solution 2

My friend proposed diferent approach: every image should use a map - either faded or just true/false array - to map where should the colours be applied. I didn't try this yet, as it's more complicated to test ad-hoc.

Altering textures in unity

It seems that texture for material can be easily altered in Unity, so the question is:

Q: How should I implement the dynamic texture coloring (generating) in Unity? Is any of my methods the good way? How should I produce the new textures, using what functions?

Rather than full code, I need information about what functions should I use. I hope other users will also profit from the general info.

To help you answering, I can guess the process will have 3 important parts:

1. Somehow get the texture of a model material (we know just the GameObject here)
2. If it hasn't been recolored already, use some algorithm to change the image properly. We'll need some pixel manipulation here
3. Apply the texture back to the model material

Answer 1

If you go the texture manipulation route, you'll need to make an additional copy of the texture stored in memory for each color, and this will increase the "loading" time of your scene. You can access the texture of a GameObject with renderer.material.mainTexture used on the GameObject that has the renderer component. Then you can use all sorts of pixel manipulation options such as SetPixel, or SetPixels to do it in batches for better performance.

There is, however, a third option that I would recommend. If you write/modify a custom shader, you can perform the color replacement at render time without significantly decreasing performance. This can be accomplished by adding a step where you convert your color output from RGB to HSV, change the Hue and Saturation, and then convert back to HSV.

By making the Hue and Saturation external parameters, you should be able to use a full range of colors including whatever you used for your marker color.

This post from the Unity forums should help with the hue shift shader.