shaders

Configuration API

A fragment shader changes the colour of each pixel in a window. This example adds a subtle blue tint to application windows. It does not blur the background; use window effects for that.

1. Create the shader

Save this as ~/.config/gnoblin/shaders/tint.frag:

uniform float strength;

vec4 gnoblin_effect(vec4 color, vec2 uv) {
    return vec4(mix(color.rgb, vec3(0.24, 0.30, 0.40), strength), color.a);
}

Create the directory first. Do not add #version or main; Gnoblin supplies them.

2. Apply it to a window

Add this to ~/.config/gnoblin/init.lua, after any gnoblin.load(...) lines:

gnoblin.window_rule {
    match = {type = "window"},
    shader = "shaders/tint.frag",
    shader_uniforms = {strength = 0.08},
}

Paths are relative to the configuration file. Absolute and ~/ paths also work. Set shader = "" in a later matching rule to remove it.

Inputs and limits

Input	Meaning
color	Pixel colour and opacity as RGBA; RGB values have not been multiplied by alpha
uv	Position within the window texture, from 0 to 1 on each axis
gnoblin_width, gnoblin_height	Surface size in logical pixels
Custom uniforms	Floats; unset values are zero

Names beginning with gnoblin_ are reserved. A later rule's uniform table replaces the earlier one.

Use GLSL 120 for desktop GL or GLSL 100 for GLES. Files must be UTF-8 and at most 64 KiB. There is no time loop, geometry shader or multi-pass API.

Reload

Files reload after edits settle for 100 ms. Invalid or missing shader files keep the previous working effect and log a gnoblin-shader warning. Fix the file to retry.

See effect tests for pixel and reload coverage.