#version 330 core
out vec4 FragColor;

in vec2 TexCoords;

uniform sampler2D screenTexture;
uniform float threshold;

void main()
{
    // Averaged, since a quarter size target would otherwise skip most of the screen's pixels
    vec2 texel = 1.0 / vec2(textureSize(screenTexture, 0));
    vec3 color = (texture(screenTexture, TexCoords + texel * vec2(-1.0, -1.0)).rgb
        + texture(screenTexture, TexCoords + texel * vec2(1.0, -1.0)).rgb
        + texture(screenTexture, TexCoords + texel * vec2(-1.0, 1.0)).rgb
        + texture(screenTexture, TexCoords + texel * vec2(1.0, 1.0)).rgb) * 0.25;

    // A single blown out specular pixel would otherwise flash a huge glow
    color = min(color, vec3(20.0));

    // Keeps the hue of whatever is over the threshold, and fades in instead of cutting off
    float brightness = max(color.r, max(color.g, color.b));
    float contribution = max(brightness - threshold, 0.0) / max(brightness, 1e-4);

    FragColor = vec4(color * contribution, 1.0);
}