western-shooter/src/rendering/shaders/post-process.frag

precision mediump float;

uniform sampler2D u_texture;
uniform vec2 u_resolution;
uniform float u_time;
uniform float u_screenShake;
uniform float u_damageFlash;
uniform float u_brightness;

varying vec2 v_texCoord;

// CRT curvature amount
const float CURVATURE = 0.03;

// Scanline intensity
const float SCANLINE_INTENSITY = 0.15;
const float SCANLINE_COUNT = 180.0;

// Vignette
const float VIGNETTE_INTENSITY = 0.3;

// Chromatic aberration
const float CHROMA_AMOUNT = 0.002;

// Bloom threshold and intensity
const float BLOOM_THRESHOLD = 0.7;
const float BLOOM_INTENSITY = 0.15;

// Apply barrel distortion for CRT curvature
vec2 curveUV(vec2 uv) {
    uv = uv * 2.0 - 1.0;
    vec2 offset = abs(uv.yx) / vec2(6.0, 4.0);
    uv = uv + uv * offset * offset * CURVATURE;
    uv = uv * 0.5 + 0.5;
    return uv;
}

// Scanlines
float scanline(vec2 uv) {
    float line = sin(uv.y * SCANLINE_COUNT * 3.14159);
    return 1.0 - SCANLINE_INTENSITY * (0.5 + 0.5 * line);
}

// Vignette effect
float vignette(vec2 uv) {
    uv = uv * 2.0 - 1.0;
    float dist = length(uv * vec2(0.8, 1.0));
    return 1.0 - smoothstep(0.7, 1.4, dist) * VIGNETTE_INTENSITY;
}

// Simple bloom by sampling bright areas
vec3 bloom(sampler2D tex, vec2 uv, vec2 resolution) {
    vec3 sum = vec3(0.0);
    float pixelSize = 1.0 / resolution.x;

    // Sample in a cross pattern
    for (float i = -2.0; i <= 2.0; i += 1.0) {
        for (float j = -2.0; j <= 2.0; j += 1.0) {
            vec2 offset = vec2(i, j) * pixelSize * 2.0;
            vec3 sample = texture2D(tex, uv + offset).rgb;

            // Only add bright pixels
            float brightness = max(max(sample.r, sample.g), sample.b);
            if (brightness > BLOOM_THRESHOLD) {
                sum += sample * (brightness - BLOOM_THRESHOLD);
            }
        }
    }

    return sum * BLOOM_INTENSITY / 25.0;
}

// Chromatic aberration
vec3 chromaticAberration(sampler2D tex, vec2 uv) {
    vec2 dir = uv - 0.5;
    float dist = length(dir);
    vec2 offset = dir * dist * CHROMA_AMOUNT;

    float r = texture2D(tex, uv + offset).r;
    float g = texture2D(tex, uv).g;
    float b = texture2D(tex, uv - offset).b;

    return vec3(r, g, b);
}

// Dithering pattern
float dither(vec2 position) {
    int x = int(mod(position.x, 4.0));
    int y = int(mod(position.y, 4.0));
    int index = x + y * 4;

    // Bayer 4x4 dither matrix
    float threshold;
    if (index == 0) threshold = 0.0;
    else if (index == 1) threshold = 8.0;
    else if (index == 2) threshold = 2.0;
    else if (index == 3) threshold = 10.0;
    else if (index == 4) threshold = 12.0;
    else if (index == 5) threshold = 4.0;
    else if (index == 6) threshold = 14.0;
    else if (index == 7) threshold = 6.0;
    else if (index == 8) threshold = 3.0;
    else if (index == 9) threshold = 11.0;
    else if (index == 10) threshold = 1.0;
    else if (index == 11) threshold = 9.0;
    else if (index == 12) threshold = 15.0;
    else if (index == 13) threshold = 7.0;
    else if (index == 14) threshold = 13.0;
    else threshold = 5.0;

    return threshold / 16.0;
}

// Quantize color to limited palette
vec3 quantize(vec3 color, float levels) {
    return floor(color * levels + 0.5) / levels;
}

void main() {
    // Apply screen shake
    vec2 uv = v_texCoord;
    if (u_screenShake > 0.0) {
        float shake = u_screenShake * 0.01;
        uv.x += sin(u_time * 50.0) * shake;
        uv.y += cos(u_time * 43.0) * shake;
    }

    // Apply CRT curvature
    vec2 curvedUV = curveUV(uv);

    // Check if we're outside the curved screen
    if (curvedUV.x < 0.0 || curvedUV.x > 1.0 || curvedUV.y < 0.0 || curvedUV.y > 1.0) {
        gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
        return;
    }

    // Sample with chromatic aberration
    vec3 color = chromaticAberration(u_texture, curvedUV);

    // Add bloom
    color += bloom(u_texture, curvedUV, u_resolution);

    // Apply scanlines
    color *= scanline(curvedUV);

    // Apply vignette
    color *= vignette(curvedUV);

    // Subtle dithering for retro feel
    vec2 pixelPos = curvedUV * u_resolution;
    float ditherValue = dither(pixelPos);
    color += (ditherValue - 0.5) * 0.03;

    // Quantize to limited color palette (subtle)
    color = mix(color, quantize(color, 32.0), 0.2);

    // Apply brightness adjustment
    color *= u_brightness;

    // Apply damage flash (red tint)
    if (u_damageFlash > 0.0) {
        color = mix(color, vec3(1.0, 0.2, 0.1), u_damageFlash * 0.4);
    }

    // Ensure we don't exceed valid range
    color = clamp(color, 0.0, 1.0);

    gl_FragColor = vec4(color, 1.0);
}