#version 460 core

in vec2 vert_texcoord;
out vec4 frag_color;

uniform sampler2D screen;

void main() {
    vec3 color = texture(screen, vert_texcoord).rgb;
    
    // FXAA implementation
    float FXAA_SPAN_MAX = 32.0;
    float FXAA_REDUCE_MUL = 1.0 / 8.0;
    float FXAA_REDUCE_MIN = 1.0 / 128.0;
    
    vec2 inverseRes = 1.0 / vec2(800, 600);
    
    vec3 luma = vec3(0.299, 0.587, 0.114);
    
    float lumaTL = dot(texture(screen, vert_texcoord + vec2(-1.0, -1.0) * inverseRes).rgb, luma);
    float lumaTR = dot(texture(screen, vert_texcoord + vec2(1.0, -1.0) * inverseRes).rgb, luma);
    float lumaBL = dot(texture(screen, vert_texcoord + vec2(-1.0, 1.0) * inverseRes).rgb, luma);
    float lumaBR = dot(texture(screen, vert_texcoord + vec2(1.0, 1.0) * inverseRes).rgb, luma);
    float lumaM = dot(color, luma);
    
    float lumaMin = min(lumaM, min(min(lumaTL, lumaTR), min(lumaBL, lumaBR)));
    float lumaMax = max(lumaM, max(max(lumaTL, lumaTR), max(lumaBL, lumaBR)));
    
    vec2 dir;
    dir.x = -((lumaTL + lumaTR) - (lumaBL + lumaBR));
    dir.y = ((lumaTL + lumaBL) - (lumaTR + lumaBR));
    
    float dirReduce = max((lumaMax - lumaMin) * FXAA_REDUCE_MUL, FXAA_REDUCE_MIN);
    float inverseDirAdjust = 1.0 / (min(abs(dir.x), abs(dir.y)) + dirReduce);
    
    dir = min(vec2(FXAA_SPAN_MAX, FXAA_SPAN_MAX),
              max(vec2(-FXAA_SPAN_MAX, -FXAA_SPAN_MAX),
                  dir * inverseDirAdjust)) * inverseRes;
    
    vec3 result = 0.5 * (
        texture(screen, vert_texcoord + dir * (1.0 / 3.0 - 0.5)).rgb +
        texture(screen, vert_texcoord + dir * (2.0 / 3.0 - 0.5)).rgb);
    
    frag_color = vec4(result, 1.0);
}


// void main() {
//     frag_color = texture(screen, vert_texcoord);
// }