In this article:
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At their core, effects are GLSL fragment shaders. Fragment shaders are sometimes called "pixel shaders," which might be more appropriate considering how they work.
Every frame, the fragment shader runs for each pixel in the output buffer. Each pixel runs the exact same shader script. The only things that change from pixel to pixel are the pixel's coordinates (referenced as gl_FragCoord.xy).
For each pixel, the shader outputs a color. Pixel coordinates come in, colors come out. That's the basic idea. An excellent introduction to shader programming is The Book of Shaders.
Lightform's effects are based on the Interactive Shader Format. Before getting started, you should review the ISF spec.
Lightform effects come in two pieces: