shader.glsl

// ----- Given this shader:

vec4 some_noise_fn() {
    return vec4(1.0, 2.0, 3.0, 4.0);
}

void main() {
    return some_noise_fn();
}

// ---- Let's replace the noise function, but now, this noise function can take in a *uniform*,
//      which is what GLSL calls variables users can dynamically pass from their game engine into the shader:

uniform float noise_strength;

vec4 other_noise_fn() {
    return vec4(5.0, 5.0, 5.0, noise_strength);
}

// ---- Here's what the final progam looks like with the function replaced (the hole filled)

uniform float noise_strength;

vec4 some_noise_fn() {
    return vec4(5.0, 5.0, 5.0, noise_strength);
}

void main() {
    return some_noise_fn();
}

// So you see, it's not just filling the "hole" (function body) - it's also mangling the AST