light_mode unshaded;

uniform sampler2D SCREEN_TEXTURE;
uniform highp vec3 tint; // Colour of the tint
uniform highp float luminance_threshold; // number between 0 and 1
uniform highp float noise_amount; // number between 0 and 1

lowp float rand (lowp vec2 n) {
  return 0.5 + 0.5 * fract (sin (dot (n.xy, vec2 (12.9898, 78.233)))* 43758.5453);
}

void fragment() {

    highp vec4 color = zTextureSpec(SCREEN_TEXTURE, FRAGCOORD.xy * SCREEN_PIXEL_SIZE);

    // convert color to grayscale using luminance
    highp float grey = dot(color.rgb, vec3(0.298, 0.5882, 0.1137));

    // calculate local threshold
    highp float threshold = grey * luminance_threshold;

    // amplify low luminance parts
    if (grey < threshold) {
        grey += (threshold - grey) * 0.5;
        if (grey > 1.0) {
            grey = 1.0;
        }
    }

    // apply night vision color tint
    color.rgb = mix(color.rgb, tint, grey);

    // add some noise for realism
    lowp float noise = rand(FRAGCOORD.xy + TIME) * noise_amount / 10.0;
    color.rgb += noise;

    COLOR = color;
}