Image mean squared error

[FrancoYudica]

Implementation of mean MSE for images

[FrancoYudica]

MSE is intended to be used as the main metric of the generated image. Here is the MSE formula.

[FrancoYudica]

Implemented MSE. As expected, it's slow because it's done in CPU. That's the reason why I decided to implement it with compute shaders.
This resource is super useful in order to learn about compute shaders implementation in godot.

[FrancoYudica]

After implementing MSE in compute shader, I got a 800x speedup, which will have a major impact in the image generation process.
It's important to note that further optimizations can be done, by using parallel reduction.