interleaving two fragment shaders: http://glsl.heroku.com/e#5174.0

main.c

precision highp float;
uniform float time;
uniform vec2 mouse;
uniform vec2 resolution;

#pragma glslify: balls = require(./balls, time=time, mouse=mouse, resolution=resolution)
#pragma glslify: sauron = require(./sauron, time=time, mouse=mouse, resolution=resolution)

int modulo(float x, float y) {
  return int(x - y * floor(x / y));
}

void main(void) {
  ivec2 m = ivec2(modulo(gl_FragCoord.x, 2.), modulo(gl_FragCoord.y, 2.));

  if(m.x == 0 || m.y == 0) {
    balls();
  } else { 
    sauron();
  }
}