// Shader that adds outlines

const float EDGE_THRESHOLD = 0.1;
const float EDGE_THICKNESS = 1.0;

const float INFINITY = 1000.0;

uniform sampler2D sampler0;
uniform sampler2D sampler1;
uniform sampler2D sampler2;

uniform float near;
uniform float far;

uniform float aspectRatio;
uniform float displayHeight;
uniform float displayWidth;

float getDepth(vec2 coord);

void main() {
    gl_FragColor = texture2D(sampler0, gl_TexCoord[0].st);

    vec2 o11 = vec2(1.0, aspectRatio)*EDGE_THICKNESS/displayWidth;
    vec2 base = gl_TexCoord[0].st - 2*o11;

    float depth = getDepth(gl_TexCoord[0].st);
    float avg = depth;
    float laplace = 24*depth;
    float sample;
    int n = 1;

    for (int i = 0; i < 5; ++i) {
        for (int j = 0; j < 5; ++j) {
            if (i != 2 || j != 2) {
                sample = getDepth(base + vec2(float(i) * o11.s, float(j) * o11.t));
                laplace -= sample;
                if (sample < 1.0) {
                    ++n;
                    avg += sample*sample;
                }
            }
        }
    }

    avg /= n;

    if (laplace > EDGE_THRESHOLD) {
        avg = clamp(avg, 0.0, 1.0);
        gl_FragColor.rgb = mix(vec3(0.0), gl_Fog.color.rgb, 0.5*avg*clamp(depth, 0.0, 1.0));
    }
}

float getDepth(vec2 coord) {
    // Return linearized depth in [0.0, 1.0]
    float depth = texture2D(sampler1, coord).x;
    float depth2 = texture2D(sampler2, coord).x;
    if (depth2 < 1.0) {
        depth = depth2;
    }

    if (depth == 1.0) {
        // Attempt to detect sky
        return INFINITY;
    }

    return (near - depth*far)/(near + depth*(far - near));
}