GameMaker shaders (GLSL ES)
GameMaker uses GLSL ES, the mobile-friendly subset of GLSL. Shaders there are written in a .fsh file next to a vertex shader. Build the effect here, then export it for a Shader asset and set the uniforms from GML.
Things to know about GLSL
- GameMaker uses GLSL ES 1.0: there is no
round()ortrunc(), and integer tricks are limited. - Texture coordinates start at the top-left; the export flips
y. - Set uniforms with
shader_set_uniform_f(shader_get_uniform(sh_mine, "time"), current_time / 1000).
Cheat sheet
| Idea | Write |
|---|---|
| Vectors | vec2 vec3 vec4 |
| Declare a value | float d = length(p); |
| A function | float circle(vec2 p, float r) { ... } |
| Matrices | mat2 mat3, multiply with M * v (this site writes v * M for lesson rotations) |
| Blend | mix(a, b, t) |
| Fractional part | fract(x) |
| Clamp to 0..1 | clamp(x, 0.0, 1.0) |
| Remainder | mod(a, b) (always positive for positive b) |
| Choose | c ? a : b |
| Angle of a vector | atan(y, x) |
| Time in seconds | time |
| Pixel position | uv (0..1, bottom-left) |
| Width / height | aspect |
| Entry point | vec4 frag(vec2 uv) { return …; } |
Handy built-ins: sin cos abs sign floor ceil fract step smoothstep clamp min max pow exp sqrt length distance dot cross normalize reflect
Gotchas
- Every pixel runs on its own, with no memory of other pixels.
- Declare a function above the place you use it.
- Prefer 2.0 over 2 in maths. This site fixes most cases for you; real engines may not.
- Loops need a small fixed count: for (int i = 0; i < 5; i++).
- GameMaker uses GLSL ES 1.0: no round(), trunc() or integer bit tricks.
Example: a glowing ring
The same shader as it is written for GameMaker:
vec4 frag(vec2 uv)
{
vec2 p = (uv - 0.5) * vec2(aspect, 1.0);
float d = length(p);
float m = 1.0 - smoothstep(0.0, 0.02, abs(d - 0.3));
vec3 bg = vec3(0.08, 0.08, 0.12);
vec3 fg = vec3(0.4, 0.9, 1.0);
return vec4(mix(bg, fg, m), 1.0);
}Exporting to GameMaker
Create a Shader asset (GLSL ES) and paste this into the .fsh file, keeping the default vertex shader. In the Draw event: shader_set(sh_mine); shader_set_uniform_f(shader_get_uniform(sh_mine, "time"), current_time / 1000); shader_set_uniform_f(shader_get_uniform(sh_mine, "aspect"), w / h); then draw a sprite or rectangle and call shader_reset(). GameMaker uses GLSL ES 1.0, so round() and trunc() are not available.
// ShaderBattle: Glowing ring
varying vec2 v_vTexcoord;
varying vec4 v_vColour;
uniform float time;
uniform float aspect;
vec4 frag(vec2 uv)
{
vec2 p = (uv - 0.5) * vec2(aspect, 1.0);
float d = length(p);
float m = 1.0 - smoothstep(0.0, 0.02, abs(d - 0.3));
vec3 bg = vec3(0.08, 0.08, 0.12);
vec3 fg = vec3(0.4, 0.9, 1.0);
return vec4(mix(bg, fg, m), 1.0);
}
void main()
{
// GameMaker's texture coordinates start at the top-left
gl_FragColor = frag(vec2(v_vTexcoord.x, 1.0 - v_vTexcoord.y));
}Questions
Do I write the vertex shader too?
No. The default vertex shader works; the export only replaces the fragment shader.
Other languages
Unity (Built-in) · Unity (URP) · Unreal · Shadertoy / WebGL · OpenGL (LWJGL, raylib) · three.js · LÖVE (Lua) · Godot · Apple (iOS, macOS) · WebGPU / Bevy