antigravity-claudekit/skills/ck-shader/SKILL.md

name, description

name	description
ck-shader	Write GLSL fragment shaders for procedural graphics. Use for generative art, procedural textures, visual effects, WebGL shaders, Three.js materials, shapes (SDF), noise, patterns, and animations.

GLSL Fragment Shaders

GPU-accelerated fragment shaders for procedural graphics, textures, and visual effects.

When to Use

• Creating procedural textures (wood, marble, clouds, terrain)
• Drawing shapes with signed distance fields (SDF)
• Generating patterns, noise, gradients, animations
• Writing custom shaders for Three.js, WebGL, Processing, ShaderToy

Don't Use When

• Simple CSS animations suffice
• Image manipulation that doesn't need GPU parallelism

Core Concepts

Each thread receives pixel position via gl_FragCoord, returns color via gl_FragColor (vec4 RGBA 0.0–1.0). Threads cannot communicate — fully stateless.

Standard Uniforms

uniform float u_time;       // Elapsed seconds
uniform vec2 u_resolution;  // Canvas size (width, height)
uniform vec2 u_mouse;       // Mouse position in pixels

Normalize coordinates: vec2 st = gl_FragCoord.xy / u_resolution;

Essential Functions

Function	Purpose
mix(a,b,t)	Linear interpolate
step(edge,x)	Hard threshold
smoothstep(e0,e1,x)	Smooth threshold
fract(x)	Fractional part (tiling)
length(v)	Vector magnitude
distance(a,b)	Euclidean distance
atan(y,x)	Angle in radians
sin/cos/pow/abs	Math (hardware-accelerated)

Quick Patterns

// Circle
float d = distance(st, vec2(0.5));
float circle = 1.0 - smoothstep(0.2, 0.21, d);

// Rectangle
vec2 bl = step(vec2(0.1), st);
vec2 tr = step(vec2(0.1), 1.0 - st);
float rect = bl.x * bl.y * tr.x * tr.y;

// Tiling
st = fract(st * 4.0);  // 4x4 grid

// Animation
float wave = sin(st.x * 10.0 + u_time) * 0.5 + 0.5;

Reference Files (Progressive Disclosure)

Fundamentals:

• references/glsl-fundamentals-data-types-vectors-precision-coordinates.md
• references/glsl-shaping-functions-step-smoothstep-curves-interpolation.md

Drawing:

• references/glsl-colors-rgb-hsb-gradients-mixing-color-spaces.md
• references/glsl-shapes-sdf-circles-rectangles-polar-distance-fields.md
• references/glsl-shapes-polygon-star-polar-sdf-combinations.md

Procedural:

• references/glsl-patterns-tiling-fract-matrices-transformations.md
• references/glsl-noise-random-perlin-simplex-cellular-voronoi.md
• references/glsl-fbm-fractional-brownian-motion-turbulence-octaves.md
• references/glsl-procedural-textures-clouds-marble-wood-terrain.md

API Reference:

• references/glsl-shader-builtin-functions-complete-api-reference.md

Tools

• Online editor: editor.thebookofshaders.com
• glslViewer: CLI tool for running .frag files
• ShaderToy: iTime, iResolution, iMouse uniforms
• LYGIA Library: https://lygia.xyz (reusable shader functions)

Resources

• The Book of Shaders: https://thebookofshaders.com
• Inigo Quilez Articles: https://iquilezles.org/articles/
• ShaderToy: https://shadertoy.com