Shaders

In short: A shader is a small program that runs on the graphics card and determines how geometry and pixels are displayed: position, color, light, shadows and surface effects.

In more detail: A graphics card is built to perform thousands of small calculations at the same time. Shaders are exactly these calculations: for each vertex or pixel the same program runs with different data. This is called parallel processing.

In Depth

Important kinds:

Shader	Task
Vertex shader	Processes each vertex of a model: position in space, displacement, animation
Fragment/pixel shader	Computes the color of each pixel: texture, light, reflection, transparency
Geometry/tessellation shader	Creates or refines geometry (more triangles from few)
Compute shader	General calculations on the GPU (physics, AI, image filters)
Ray-tracing shader	Computing light rays for realistic lighting

Sequence in the graphics pipeline: Model data → vertex shader → rasterization (triangles become pixels) → fragment shader → image.

Languages: GLSL (OpenGL), HLSL (DirectX, Unity), WGSL (WebGPU), Metal Shading Language (Apple), SPIR-V (Vulkan). Visual: Shader Graph (Unity), material editor (Unreal).

Example (GLSL fragment shader):

void main() {
    // color from the texture, darkened depending on light
    vec3 color = texture(tex, uv).rgb * max(dot(normal, lightDir), 0.0);
    output = vec4(color, 1.0);
}

Use:

• Lighting, shadows, water, smoke, skin, hair, fog.
• Post-processing: blur (bloom), color correction, anti-aliasing.
• Art styles: cel shading (comic look), pixel shaders, hologram effects.
• Not only games: films (render shaders), calculations, AI.

Cost: Complex shaders slow the frame rate. “Compiling shaders” at first start makes games load long (shader cache).

See also: Game engine, Unity, 3D modeling