#version 410

uniform sampler2D texture1;
in vec2 uvV;

out vec4 fragColor;
uniform float opacity = 1.0;
uniform float zNear = 0.1;
uniform float zFar = 500.0;

uniform vec2 meScreenSize;

// capture the depth from texture1.x...
// see: http://stackoverflow.com/questions/6652253/getting-the-true-z-value-from-the-depth-buffer for some helpful math

/*
// == Post-process frag shader ===========================================
uniform sampler2D depthBuffTex;
uniform float zNear;
uniform float zFar;
varying vec2 vTexCoord;
void main(void)
{
    float z_b = texture2D(depthBuffTex, vTexCoord).x;
    float z_n = 2.0 * z_b - 1.0;
    float z_e = 2.0 * zNear * zFar / (zFar + zNear - z_n * (zFar - zNear));
}
*/


float depthAt(vec2 pixelCoord)
{
    float depthSample = texture(texture1, pixelCoord / meScreenSize).r;

    float z_n = 2.0 * depthSample - 1.0;
    float z_e = 2.0 * zFar * zNear / (zFar + zNear - z_n * (zFar - zNear));
    
    return z_e;
}

void main (void)
{
//    vec2 co = gl_FragCoord.xy / vec2(meScreenSize.x, meScreenSize.y);
//
//    float n = 0.1;
//    float f = 500.0;
//    
//    float depthSample = texture(texture1, uvV).r;
//
//    float z_n = 2.0 * depthSample - 1.0;
//    
//    float z_e = 2 * n * f / (f + n - z_n * (f - n));
    
    float z00 = depthAt(gl_FragCoord.xy);
    float z0p = depthAt(gl_FragCoord.xy + vec2(0,1));
    float z0n = depthAt(gl_FragCoord.xy + vec2(0,-1));
    float zp0 = depthAt(gl_FragCoord.xy + vec2(1,0));
    float zn0 = depthAt(gl_FragCoord.xy + vec2(-1,0));
    
    float ang0p = abs(z00 - z0p) > 0.5 ? 0 : 1;
    float ang0n = abs(z00 - z0p) > 0.5 ? 0 : 1;
    float angp0 = abs(z00 - zp0) > 0.5 ? 0 : 1;
    float angn0 = abs(z00 - zn0) > 0.5 ? 0 : 1;

    float g = (ang0n != ang0p) || (angn0 != angp0) ? 0 : 1;

    z0p -= z00;
    z0n -= z00;
    zp0 -= z00;
    zn0 -= z00;
    
    const float thresh = 0.001;
    bool enuf01 = abs(z0p) > thresh || abs(z0n) > thresh;
    bool enuf10 = abs(zp0) > thresh || abs(zn0) > thresh;
    
    bool sgn0p = z0p > 0;
    bool sgn0n = z0n > 0;
    bool sgnp0 = zp0 > 0;
    bool sgnn0 = zn0 > 0;
    g *= (enuf01 && sgn0p == sgn0n) || (enuf10 && sgnp0 == sgnn0) ? 0 : 1;
//    float del = max(abs(z00 - z01), abs(z00 - z10));
//    float g = del > 0.5 ? 0 : 1;
//    float z_e = depthAt(gl_FragCoord.xy);
//    z_e -= depthAt(gl_FragCoord.xy + vec2(1,1));
//    float g = z_e / 100;
    
    g *= z00 / 75;
    fragColor = texture(texture1, uvV);
    fragColor = vec4(fragColor.rrr, opacity);
    
    fragColor = vec4(g,g,g,1);
}