Add support for uniforms.

[lord-123]

Add support for custom uniforms that:

• Update periodically.
• Can be c code or command line utils.
• Specify glsl data type.

Being worked on in the uniforms branch

[clort81]

Didnt want to create an issue, just thanks for writing this.
I've been footling around with this sort of thing on my arm SBC's with shadertoy glsls and forcing window to 'below other windows'.
I have a couple glsls I made here somewhere but I'm not happy with the high gpu use so far.
I think that, with a compositor the pixel shader can render to an offscreen buffer then render to fullscreen with bilinear scaling, which could solve my gpu load at 4k.
clort_background_glsl_clouds.webm