New feature: calculate normal from height map (GLSL and HLSL)

[shadielhajj]

When displacing a grid based on a height map texture, we need to calculate the normals. This function does it for us.

Here's an example of 2048x2048 grid being displaced by a simple noise texture. Normals are calculated directly from the height maps using sample/normalFromTexture.

[patriciogonzalezvivo]

Nice one!
Just for the record. You can also use this one https://lygia.xyz/sample/bumpMap ( which calculates derivatives using this other one https://lygia.xyz/sample/derivative) it makes more samples. I like your approach.

Thank you again!

[shadielhajj]

Thanks for the head up @patriciogonzalezvivo. I missed sample/bumpMap. Works nicely indeed.
HLSL version of sample/derivative is broken btw. I'll make a PR with a fix in a sec.

[patriciogonzalezvivo]

Nit: I was wondering about the name 'sampleNormalFromTextue' wouldn't be more clear 'sampleNormalFromHeightmap'? Being a sampler implies is sampling from a texture. Just a thought. Happy to go with your gut feeling

[shadielhajj]

@patriciogonzalezvivo agreed. I was also hesitating. Let's go with normalFromHeightmap. I'll PR.