#version 430 core
in vec2 vTexPos;
out vec4 fColor;
const vec2 winSize = vec2 (300,300);
// note that the above opening bracket should be the first in this file
// this is so that the window size can be extracted and the shader recompiled on
// the fly
uniform sampler2D screenTexture;

const float hOff = 3.0 / winSize.x;
const float vOff = 3.0 / winSize.y;
const float frac = 1.0 / 9;
const vec2 off[9] = vec2[]
    ( vec2( hOff, vOff )
    , vec2( hOff,  0.0 )
    , vec2( hOff,-vOff )
    , vec2(  0.0, vOff )
    , vec2(  0.0,  0.0 )
    , vec2(  0.0,-hOff )
    , vec2(-hOff, vOff )
    , vec2(-hOff,  0.0 )
    , vec2(-hOff,-vOff )
    );
const vec2 fiveOff[5] = vec2[]
    ( vec2( vOff,0.0 )
    , vec2( 0.0,hOff )
    , vec2( 0.0,0.0 )
    , vec2( 0.0,-hOff )
    , vec2( -vOff,0.0 )
    );
vec4 combinef (vec4 ac, vec4 bc)
//{ return vec4 (max(ac.x,bc.x),max(ac.y,bc.y),max(ac.z,bc.z),ac.w + bc.w -
//        ac.w*bc.w);
//{ return vec4 (max(ac.x,bc.x),max(ac.y,bc.y),max(ac.z,bc.z),ac.w + bc.w);
{ return vec4 (ac.rgb + bc.rgb * bc.a , ac.a + bc.a );
}
void main()
{
    vec4 sampleTex[9];
    for(int i=0; i<9; i++)
    {
        sampleTex[i] = vec4(texture(screenTexture, vTexPos + off[i]));
    }
    vec4 sampleFive[5];
    for(int i=0; i<5; i++)
    {
        sampleFive[i] = vec4(texture(screenTexture, vTexPos + fiveOff[i]));
    }
    vec4 col = vec4(0,0,0,0);
    for (int i = 0; i < 9; i++)
        col = combinef(col,sampleTex[i]);
        //col += sampleTex[i] * frac;
    float alph = 0.0;
    for (int i = 0; i < 9; i++)
        //alph += sampleTex[i].a;
        alph = max(alph, 0.5 * sampleTex[i].a);
    alph = max(sampleTex[4].a, alph);
        //
    //fColor = col;
    fColor = vec4(col.rgb/col.a,alph);
    //if (col.a == 0.0)
    //{ fColor = vec4(0,0,0,0); }
    //else
    //{ fColor = vec4( col.r/col.a , col.g/col.a , col.b/col.a, col.a/9.0); }
}