An example of using OpenGL framebuffers to perform post-processing with multiple shader passes using the .NET OpenTK library. This does use my eyecandy library, but only as a convenience to avoid duplicating the simple Shader class (basically it compiles the shaders and has a few helper functions to set attributes and uniforms).
Note this assumes at least OpenGL 4.6 availability (which means it'll work on Windows and Linux, but not Mac or low-spec devices like the Raspberry Pi.)
This demo is a stack of five frag shaders using three framebuffers. The vertex shader is a simple pair of triangles that covers the entire display window. The frag shaders are mostly adapted from Shadertoy content.
By default all five passes are output. You can hit the spacebar to short-circuit the shader passes and output the results of each stage.
The first pass renders a colorful plasma field to framebuffer 0.
The second pass desaturates the plasma field (using the plasma texture in framebuffer 0 as an input uniform) and renders the results to framebuffer 1.
The third pass runs a Sobel edge-detection algorithim (using the desaturated texture in framebuffer 1 as an input) and renders the results to framebuffer 2.
The fourth pass applies a black-and-white semi-transparent cloudy effect to the edges of the image (using the edge-detection texture in framebuffer 2 as an input) and renders the results to framebuffer 1.
The fifth and final pass colorizes the image. It uses both the original plasma texture still in framebuffer 0 as the source of color data, and mixes it with the black and white texture in framebuffer 1 which has the combined edge-detection and cloudy effects. This is rendered to framebuffer 2.
Finally, framebuffer 2 is blitted to the default backbuffer, the buffers are swapped and the whole thing appears on-screen.
Huge thanks to themixedupstuff and BoyBayKiller on the OpenTK discord channel for helping me to understand how to juggle multiple framebuffers.