// set by the vertex shader
varying vec2 tex_coord;
uniform sampler2DRect colorTexture;
uniform sampler2DRect depthTexture;
uniform sampler2DRect normalTexture;
uniform float near;
uniform float far;
uniform int width;
uniform int height;
vec2 top;
vec2 bottom;
vec2 left;
vec2 right;
const float offset = 0.05;

void main(void)
{
    top = vec2(tex_coord.x, tex_coord.y - 1);
    bottom = vec2(tex_coord.x, tex_coord.y + 1);
    left = vec2(tex_coord.x - 1, tex_coord.y);
    right = vec2(tex_coord.x + 1, tex_coord.y);

    float topD = texture2DRect(depthTexture, top);
    float bottomD = texture2DRect(depthTexture, bottom);
    float leftD = texture2DRect(depthTexture, left);
    float rightD = texture2DRect(depthTexture, right);

    //converting the values obtained from the depth buffer
    float topZ = (near*far)/far-topD*(far-near);
    float bottomZ = (near*far)/far-bottomD*(far-near);
    float leftZ = (near*far)/far-leftD*(far-near);
    float rightZ = (near*far)/far-rightD*(far-near);

    float magnitude = abs(rightZ - leftZ) + abs(bottomZ - topZ);
    if(magnitude > offset)
    {
        // make it black
        gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
    }
    else
    {
        // leave it as is.
        gl_FragColor = texture2DRect(colorTexture,tex_coord);
    }
    // render a color based on the texture coordinate

    //gl_FragCoord = gl_FragCoord;
}