driftwm renders the canvas background using a GLSL fragment shader. You can write your own to replace the default dot grid.

The shader runs once per pixel every frame the viewport changes. It receives the pixel's position and the viewport's camera offset, and outputs a color. The result covers the entire output behind all windows.

v_coords * size gives screen-local pixel coordinates (top-left = 0,0). Adding u_camera converts to canvas coordinates — this is how the background scrolls with the viewport.

Set gl_FragColor to an RGBA vec4. Multiply by alpha to respect compositor opacity:

gl_FragColor = vec4(color, 1.0) * alpha;

Solid color that shifts hue based on viewport position:

precision mediump float;

varying vec2 v_coords;
uniform vec2 size;
uniform float alpha;
uniform vec2 u_camera;

void main() {
    vec2 canvas = (v_coords * size + u_camera) * 0.001;
    vec3 col = vec3(
        sin(canvas.x) * 0.5 + 0.5,
        sin(canvas.y) * 0.5 + 0.5,
        0.5
    );
    gl_FragColor = vec4(col, 1.0) * alpha;
}

• GLSL ES 1.0: smithay auto-prepends #version 100. Don't add your own version directive. Use precision mediump float; or highp for noise.
• Canvas coords: The standard pattern is vec2 canvas = (v_coords * size + u_camera) * scale; where scale controls the feature size (smaller = larger features).
• Float precision: u_camera can be large (thousands of pixels from origin). If your shader uses mod() or fract() on canvas coords, reduce first: mod(u_camera, period) instead of mod(canvas, period). See dot_grid.glsl for an example. Noise-based shaders using floor()/fract() internally are naturally resilient since the hash functions wrap.
• No time uniform: driftwm only re-renders when the viewport moves. Animated shaders are not currently supported.
• Colors as constants: Define colors, spacing, and other tunables as GLSL const values at the top of your shader. This keeps everything in one file — no config round-trip needed.
• Shipped examples: See assets/shaders/ for dot grid, compass grid, noise clouds, and dark sea patterns.

Set shader_path under [background] in your config:

[background]
shader_path = "~/shaders/my_bg.glsl"

Priority: shader_path > tile_path > built-in dot grid.

The config is automatically reloaded when the file changes. The shader is re-read from disk on every reload, so touch the config to pick up shader edits:

touch ~/.config/driftwm/config.toml

To bind this to a key, add to your config:

[keybindings]
"mod+shift+c" = "spawn touch ~/.config/driftwm/config.toml"