work

uniform sampler2D texture;
uniform float width;
uniform float border;

//third step in the lighting algorithm.
//reduces the occlusion map to 2 pixels horizontally
//(each pass halves the texture size horizontally)

/*the original reduction shader from Zima only used min(pixel, pixelRight), adding the left pixel
somehow made it work better, i dont know why, should technically be the same thing right? maybe my
downscaling method is sloppy or theres some mipmapping going on im not aware of, even though i only
scale down in the x axis, but i spent weeks on this already and just dont care anymore*/

void main()
{
    float pixeltopixeldistance = 1.0f / width;

    //odd pixel?
    bool thisrow = fract(gl_TexCoord[0].x * width / 2.0f) < 0.5f;

    vec2 otherpixel = texture2D(texture, gl_TexCoord[0].xy - vec2(pixeltopixeldistance,0)).rg; //color to the right

    vec2 color     = texture2D(texture, gl_TexCoord[0].xy);
    vec2 result = vec2(min(color, otherpixel));  //, min(min(color.g, colorL.g) , colorR.g));
    if (!thisrow && !(gl_TexCoord[0].x < 0.5f && gl_TexCoord[0].x + pixeltopixeldistance > 0.5f))
        gl_FragColor = vec4(min(color, otherpixel),0,1);
}

/*
void main()
{
    float pixeltopixeldistance = 1.0f / width;

    //odd pixel?
    bool thisrow = fract(gl_TexCoord[0].x * width / 2.0f) < 0.5f;

    vec2 pixeloffset = vec2(pixeltopixeldistance,0).rg;
    if(thisrow) pixeloffset *= -1.f;

    vec2 otherpixel = texture2D(texture, clamp(gl_TexCoord[0].xy + pixeloffset, vec2(0.0f, 0.0f), vec2(1.0f,0.0f)));

    vec2 color  = texture2D(texture, gl_TexCoord[0].xy);
    vec2 result = min(color, otherpixel);  //, min(min(color.g, colorL.g) , colorR.g));
    if (
        !thisrow &&
        !((gl_TexCoord[0].x < border) && (gl_TexCoord[0].x + pixeloffset.x >= border)) &&
        !((gl_TexCoord[0].x > border) && (gl_TexCoord[0].x + pixeloffset.x <= border))
    )
        gl_FragColor = vec4(min(color, otherpixel), 0, 1);
}
*/

/*
void main()
{
    float pixeltopixeldistance = 1.0f / width;

    //odd pixel?
    bool thisrow = fract(gl_TexCoord[0].x * width / 2.0f) < 0.5f;

    vec2 otherpixel;
    if(!thisrow)    otherpixel = texture2D(texture, gl_TexCoord[0].xy - vec2(pixeltopixeldistance,0)).rg; //color to the left
            else    otherpixel = texture2D(texture, gl_TexCoord[0].xy + vec2(pixeltopixeldistance,0)).rg; //color to the right

    vec2 color  = texture2D(texture, gl_TexCoord[0].xy);
    vec2 result = vec2(min(color, otherpixel));  //, min(min(color.g, colorL.g) , colorR.g));
    gl_FragColor = vec4(min(color, otherpixel),0,1);
}
*/


/*
void main()
{
    float pixeltopixeldistance = 1.0f / width;

    //odd pixel?
    bool thisrow = fract(gl_TexCoord[0].x * width / 2.0f) < 0.5f;

    vec2 otherpixel = texture2D(texture, gl_TexCoord[0].xy - vec2(pixeltopixeldistance,0)).rg; //color to the right

    vec2 color     = texture2D(texture, gl_TexCoord[0].xy);
    vec2 result = vec2(min(color, otherpixel));  //, min(min(color.g, colorL.g) , colorR.g));
    if (!thisrow && !(gl_TexCoord[0].x < 0.5f && gl_TexCoord[0].x + pixeltopixeldistance > 0.5f))
        gl_FragColor = vec4(min(color, otherpixel),0,1);
}
*/
/*
void main(){
    vec2 color = texture2D(texture, gl_TexCoord[0].xy);
    vec2 colorR = texture2D(texture, clamp(gl_TexCoord[0].xy + vec2(1.0f / width, 0.0f), vec2(0.0f, 0.0f), vec2(1.0f,1.0f)));
    if(gl_TexCoord[0].x < border && gl_TexCoord[0].x + 1.0f / width > border)
        discard;
    else gl_FragColor = vec4(min(color, colorR), 0, 1);

}
*/