//
// Simple passthrough fragment shader
//
uniform vec2  size;
uniform float amount;
uniform vec3  fadeColor;
uniform float offset;

varying vec2 v_vTexcoord;
varying vec4 v_vColour;

#define fadeColorDistance 0.5

// BEGIN PASTE //

// Function from:
// https://stackoverflow.com/questions/4200224/random-noise-functions-for-glsl
float rand(vec2 co){
    return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);
}

// These 3 functions from:
// https://gist.github.com/patriciogonzalezvivo/670c22f3966e662d2f83
float rand(float n){return fract(sin(n) * 43758.5453123);}

float noise(float p){
    float fl = floor(p);
  float fc = fract(p);
    return mix(rand(fl), rand(fl + 1.0), fc);
}

float noise(vec2 n) {
    const vec2 d = vec2(0.0, 1.0);
  vec2 b = floor(n), f = smoothstep(vec2(0.0), vec2(1.0), fract(n));
    return mix(mix(rand(b), rand(b + d.yx), f.x), mix(rand(b + d.xy), rand(b + d.yy), f.x), f.y);
}

// END PASTE //

void main()
{
    vec4 col = v_vColour * texture2D( gm_BaseTexture, v_vTexcoord );

    vec2 pos = vec2(
        floor( v_vTexcoord.x / size.x ) * size.x + offset,
        floor( v_vTexcoord.y / size.y ) * size.y + offset
    );

    float n = noise( pos * 12.0 );
    float f = max( amount - fadeColorDistance, 0.0 );

    if ( n < amount ) {
        col.a *= 1.0;
        if ( n > f ) {
            float fa = min( ( n - f ) / f, 1.0 );

            col = vec4(
                mix( col.r, fadeColor.r, fa ),
                mix( col.g, fadeColor.g, fa ),
                mix( col.b, fadeColor.b, fa ),
                col.a
            );
        }
    }
    else {
        float ff = min( amount + fadeColorDistance, 1.0 );

        if ( n < ff ) {
            col = vec4(
                fadeColor.rgb,
                col.a * ( ff - n ) / ff
            );
        } else {
            col.a *= 0.0;
        }
    }
    gl_FragColor = col;
}