Shader: a type of computer program (set of instructions) for programmable GPUs.

• GPU: Graphics Processing Unit; which are designed with parallel/simultaneous-processing/transformation of frames/buffers/loads of data in mind.

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The same shader program/function/instruction is executed for variable input data.

👆 When you write shaders, that is a very important paradigm. It is (arguably?) **the central ‘**mental shift’ for someone coming from “ordinary”, sequential-data CPU programming.

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If a CPU (Central Processing Unit) is a sports car, then a GPU is a bus.

• One person can be rapidly transported across/around the city, zipping through any branching path(s) on a whim, or a bus full of people can be efficiently transported between fixed waypoints.
• GPUs operate on graphics-related data via a pipeline of bulk data-processing steps/stages.

CPUs are typically more freely programmable and utilized than GPUs, which are designed to operate on bulk workloads of data through specific stages, standard/common to modern graphics tasks.

Thus, there are different types of shaders;

• Vertex, Geometry: per vertex, primitive.
• Fragment/Pixel: per-pixel data processing.

And, also—

• Compute: not part of the graphics pipeline, typically for “GPGPU” (general-purpose GPU utility).

Data for graphics/rendering is typically processed in stages from defining the geometry, then shading/colouring surfaces ← which makes for a logical, and more efficient, standardized system.

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“Shader” is from their original utility, which was to ‘shade’ digital/virtual surface geometry.

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Your screen is a grid of ‘pixels’ (”picture elements”); emissive [light-emitting] units of RGB colour.

• If you describe something via mathematical functions, then you can sample the result.

Your screen is a discretized output grid.

You might imagine (most, typical-) video games as complex, interactive descriptions of 3D worlds. They exist a system of systems; some framework like the static geometry of a level, and the fundamental programming/instructions/command which a virtual universe simulates.

• f(x) == f(x); input (if any) → data processing, generation → output.
• Visuals, geometry; sampled and rendered relative to the system ‘camera’.