an example glslify main module.

glslify.c

// precision statements in child programs are ripped out.
// only the main module's precision statements will remain.
precision highp float;
precision highp vec2;

// only "attribute|varying|uniform" vars defined by the root program
// will be emitted.
attribute vec2 lol;

// a generic require statement.
// NB: quotes are not valid *anywhere* in a GLSL program.
// TODO: allow arbitrary expressions on the right hand side of a mapping.
#pragma glslify: add_three = require(./file2)

// child shaders may define "attribute" (incoming vertices) or "varying"
// (outgoing vertices). in that case, the requiring program can either link
// them to an existing variable at this level, or leave them for a parent requiring
// module to define.
//
// if no module defines a mapping for the "attribute|varying|uniform" var, an
// exception will be thrown an the program won't compile.
#pragma glslify: something = require(./file3, thing=lol)

// looking up modules from `node_modules/` works too -- if the package.json
// does not specify a `glslify` or `main`, then it will use `index.glsl`.
#pragma glslify: our_modulo = require(glsl-test)

void main(void) {
  int result = our_modulo(something(add_three(3)), 5);

  // TODO: when gl_Position (or gl_FragColor) is used in a submodule,
  // export them as required names (like attributes and friends).
  gl_Position = vec4(result, result, result, 1.0);
}

// you may export a declaration from your module (but one, and only one.)
#pragma glslify: export(main)

output.c

precision highp float;
precision highp vec2;
attribute vec2 lol;
int b_x_add_four(int y) {
  return y + 4;
}
int a_x_main(int z) {
  return b_x_add_four(z) - 1;
}
vec2 c_x_test(int z) {
  return b_x_add_four(z);
}
int e_x_modulo(int a, int b) {
  return a % b;
}
void main(void) {
  int result = e_x_modulo(c_x_test(a_x_main(3)), 5);
  gl_Position = vec4(result, result, result, 1.0);
}