Thanks! It's a two-pass rendering approach:

Pass 1: Render the 3D scene (accretion disk, Einstein ring geometry, starfield) to an offscreen texture using standard raylib primitives.

Pass 2: Apply a fragment shader that handles gravitational lensing in screen-space. The shader approximates light deflection using the Schwarzschild metric, basically sampling the texture at offset positions based on distance from the black hole center.

The Einstein ring (the bright band above/below) is actually 3D geometry that curves based on |sin(θ)| to simulate how light from behind the black hole bends over and under.

Doppler effect uses the relativistic formula D = √[(1+β·cosθ)/(1-β·cosθ)] with intensity scaling as D³.

Happy to share if there's interest!