glsl_playground/basic/color_panes.glsl

#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform vec2 u_mouse;

void main(){
    vec2 st = gl_FragCoord.xy/u_resolution.xy;

    gl_FragColor = vec4(floor(vec3(st, u_mouse.x/u_resolution.x)+0.5),1.0);
}