/* OmniScale is derived from the pattern based design of HQnx, but with the following general differences:
    - The actual output calculating was completely redesigned as resolution independent graphic generator. This allows
      scaling to any factor.
    - HQnx approximations that were good enough for a 2x/3x/4x factor were refined, creating smoother gradients.
    - "Quarters" can be interpolated in more ways than in the HQnx filters 
    - If a pattern does not provide enough information to determine the suitable scaling interpolation, up to 16 pixels 
      per quarter are sampled (in contrast to the usual 9) in order to determine the best interpolation. 
 */

/* We use the same colorspace as the HQ algorithms. */
STATIC vec3 rgb_to_hq_colospace(vec4 rgb)
{
    return vec3( 0.250 * rgb.r + 0.250 * rgb.g + 0.250 * rgb.b,
                 0.250 * rgb.r - 0.000 * rgb.g - 0.250 * rgb.b,
                -0.125 * rgb.r + 0.250 * rgb.g - 0.125 * rgb.b);
}


STATIC bool is_different(vec4 a, vec4 b)
{
    vec3 diff = abs(rgb_to_hq_colospace(a) - rgb_to_hq_colospace(b));
    return diff.x > 0.018 || diff.y > 0.002 || diff.z > 0.005;
}

#define P(m, r) ((pattern & (m)) == (r))

STATIC vec4 scale(sampler2D image, vec2 position, vec2 input_resolution, vec2 output_resolution)
{
    // o = offset, the width of a pixel
    vec2 o = vec2(1, 1);
    
    /* We always calculate the top left quarter.  If we need a different quarter, we flip our co-ordinates */

    // p = the position within a pixel [0...1]
    vec2 p = fract(position * input_resolution);

    if (p.x > 0.5) {
        o.x = -o.x;
        p.x = 1.0 - p.x;
    }
    if (p.y > 0.5) {
        o.y = -o.y;
        p.y = 1.0 - p.y;
    }

    vec4 w0 = texture_relative(image, position, vec2( -o.x, -o.y));
    vec4 w1 = texture_relative(image, position, vec2(    0, -o.y));
    vec4 w2 = texture_relative(image, position, vec2(  o.x, -o.y));
    vec4 w3 = texture_relative(image, position, vec2( -o.x,    0));
    vec4 w4 = texture_relative(image, position, vec2(    0,    0));
    vec4 w5 = texture_relative(image, position, vec2(  o.x,    0));
    vec4 w6 = texture_relative(image, position, vec2( -o.x,  o.y));
    vec4 w7 = texture_relative(image, position, vec2(    0,  o.y));
    vec4 w8 = texture_relative(image, position, vec2(  o.x,  o.y));

    int pattern = 0;
    if (is_different(w0, w4)) pattern |= 1 << 0;
    if (is_different(w1, w4)) pattern |= 1 << 1;
    if (is_different(w2, w4)) pattern |= 1 << 2;
    if (is_different(w3, w4)) pattern |= 1 << 3;
    if (is_different(w5, w4)) pattern |= 1 << 4;
    if (is_different(w6, w4)) pattern |= 1 << 5;
    if (is_different(w7, w4)) pattern |= 1 << 6;
    if (is_different(w8, w4)) pattern |= 1 << 7;

    if ((P(0xBF,0x37) || P(0xDB,0x13)) && is_different(w1, w5)) {
        return mix(w4, w3, 0.5 - p.x);
    }
    if ((P(0xDB,0x49) || P(0xEF,0x6D)) && is_different(w7, w3)) {
        return mix(w4, w1, 0.5 - p.y);
    }
    if ((P(0x0B,0x0B) || P(0xFE,0x4A) || P(0xFE,0x1A)) && is_different(w3, w1)) {
        return w4;
    }
    if ((P(0x6F,0x2A) || P(0x5B,0x0A) || P(0xBF,0x3A) || P(0xDF,0x5A) ||
         P(0x9F,0x8A) || P(0xCF,0x8A) || P(0xEF,0x4E) || P(0x3F,0x0E) ||
         P(0xFB,0x5A) || P(0xBB,0x8A) || P(0x7F,0x5A) || P(0xAF,0x8A) ||
         P(0xEB,0x8A)) && is_different(w3, w1)) {
        return mix(w4, mix(w4, w0, 0.5 - p.x), 0.5 - p.y);
    }
    if (P(0x0B,0x08)) {
        return mix(mix(w0 * 0.375 + w1 * 0.25 + w4 * 0.375, w4 * 0.5 + w1 * 0.5, p.x * 2.0), w4, p.y * 2.0);
    }
    if (P(0x0B,0x02)) {
        return mix(mix(w0 * 0.375 + w3 * 0.25 + w4 * 0.375, w4 * 0.5 + w3 * 0.5, p.y * 2.0), w4, p.x * 2.0);
    }
    if (P(0x2F,0x2F)) {
        float dist = length(p - vec2(0.5));
        float pixel_size = length(1.0 / (output_resolution / input_resolution));
        if (dist < 0.5 - pixel_size / 2) {
            return w4;
        }
        vec4 r;
        if (is_different(w0, w1) || is_different(w0, w3)) {
            r = mix(w1, w3, p.y - p.x + 0.5);
        }
        else {
            r = mix(mix(w1 * 0.375 + w0 * 0.25 + w3 * 0.375, w3, p.y * 2.0), w1, p.x * 2.0);
        }

        if (dist > 0.5 + pixel_size / 2) {
            return r;
        }
        return mix(w4, r, (dist - 0.5 + pixel_size / 2) / pixel_size);
    }
    if (P(0xBF,0x37) || P(0xDB,0x13)) {
        float dist = p.x - 2.0 * p.y;
        float pixel_size = length(1.0 / (output_resolution / input_resolution)) * sqrt(5.0);
        if (dist > pixel_size / 2) {
            return w1;
        }
        vec4 r = mix(w3, w4, p.x + 0.5);
        if (dist < -pixel_size / 2) {
            return r;
        }
        return mix(r, w1, (dist + pixel_size / 2) / pixel_size);
    }
    if (P(0xDB,0x49) || P(0xEF,0x6D)) {
        float dist = p.y - 2.0 * p.x;
        float pixel_size = length(1.0 / (output_resolution / input_resolution)) * sqrt(5.0);
        if (p.y - 2.0 * p.x > pixel_size / 2) {
            return w3;
        }
        vec4 r = mix(w1, w4, p.x + 0.5);
        if (dist < -pixel_size / 2) {
            return r;
        }
        return mix(r, w3, (dist + pixel_size / 2) / pixel_size);
    }
    if (P(0xBF,0x8F) || P(0x7E,0x0E)) {
        float dist = p.x + 2.0 * p.y;
        float pixel_size = length(1.0 / (output_resolution / input_resolution)) * sqrt(5.0);

        if (dist > 1.0 + pixel_size / 2) {
            return w4;
        }

        vec4 r;
        if (is_different(w0, w1) || is_different(w0, w3)) {
            r = mix(w1, w3, p.y - p.x + 0.5);
        }
        else {
            r = mix(mix(w1 * 0.375 + w0 * 0.25 + w3 * 0.375, w3, p.y * 2.0), w1, p.x * 2.0);
        }

        if (dist < 1.0 - pixel_size / 2) {
            return r;
        }

        return mix(r, w4, (dist + pixel_size / 2 - 1.0) / pixel_size);
    }

    if (P(0x7E,0x2A) || P(0xEF,0xAB)) {
        float dist = p.y + 2.0 * p.x;
        float pixel_size = length(1.0 / (output_resolution / input_resolution)) * sqrt(5.0);

        if (p.y + 2.0 * p.x > 1.0 + pixel_size / 2) {
            return w4;
        }

        vec4 r;

        if (is_different(w0, w1) || is_different(w0, w3)) {
            r = mix(w1, w3, p.y - p.x + 0.5);
        }
        else {
            r = mix(mix(w1 * 0.375 + w0 * 0.25 + w3 * 0.375, w3, p.y * 2.0), w1, p.x * 2.0);
        }

        if (dist < 1.0 - pixel_size / 2) {
            return r;
        }

        return mix(r, w4, (dist + pixel_size / 2 - 1.0) / pixel_size);
    }

    if (P(0x1B,0x03) || P(0x4F,0x43) || P(0x8B,0x83) || P(0x6B,0x43)) {
        return mix(w4, w3, 0.5 - p.x);
    }

    if (P(0x4B,0x09) || P(0x8B,0x89) || P(0x1F,0x19) || P(0x3B,0x19)) {
        return mix(w4, w1, 0.5 - p.y);
    }

    if (P(0xFB,0x6A) || P(0x6F,0x6E) || P(0x3F,0x3E) || P(0xFB,0xFA) ||
        P(0xDF,0xDE) || P(0xDF,0x1E)) {
        return mix(w4, w0, (1.0 - p.x - p.y) / 2.0);
    }

    if (P(0x4F,0x4B) || P(0x9F,0x1B) || P(0x2F,0x0B) ||
        P(0xBE,0x0A) || P(0xEE,0x0A) || P(0x7E,0x0A) || P(0xEB,0x4B) ||
        P(0x3B,0x1B)) {
        float dist = p.x + p.y;
        float pixel_size = length(1.0 / (output_resolution / input_resolution));

        if (dist > 0.5 + pixel_size / 2) {
            return w4;
        }

        vec4 r;
        if (is_different(w0, w1) || is_different(w0, w3)) {
            r = mix(w1, w3, p.y - p.x + 0.5);
        }
        else {
            r = mix(mix(w1 * 0.375 + w0 * 0.25 + w3 * 0.375, w3, p.y * 2.0), w1, p.x * 2.0);
        }

        if (dist < 0.5 - pixel_size / 2) {
            return r;
        }

        return mix(r, w4, (dist + pixel_size / 2 - 0.5) / pixel_size);
    }

    if (P(0x0B,0x01)) {
        return mix(mix(w4, w3, 0.5 - p.x), mix(w1, (w1 + w3) / 2.0, 0.5 - p.x), 0.5 - p.y);
    }

    if (P(0x0B,0x00)) {
        return mix(mix(w4, w3, 0.5 - p.x), mix(w1, w0, 0.5 - p.x), 0.5 - p.y);
    }

    float dist = p.x + p.y;
    float pixel_size = length(1.0 / (output_resolution / input_resolution));

    if (dist > 0.5 + pixel_size / 2) {
        return w4;
    }

    /* We need more samples to "solve" this diagonal */
    vec4 x0 = texture_relative(image, position, vec2( -o.x * 2.0, -o.y * 2.0));
    vec4 x1 = texture_relative(image, position, vec2( -o.x      , -o.y * 2.0));
    vec4 x2 = texture_relative(image, position, vec2(  0.0      , -o.y * 2.0));
    vec4 x3 = texture_relative(image, position, vec2(  o.x      , -o.y * 2.0));
    vec4 x4 = texture_relative(image, position, vec2( -o.x * 2.0, -o.y      ));
    vec4 x5 = texture_relative(image, position, vec2( -o.x * 2.0,  0.0      ));
    vec4 x6 = texture_relative(image, position, vec2( -o.x * 2.0,  o.y      ));

    if (is_different(x0, w4)) pattern |= 1 << 8;
    if (is_different(x1, w4)) pattern |= 1 << 9;
    if (is_different(x2, w4)) pattern |= 1 << 10;
    if (is_different(x3, w4)) pattern |= 1 << 11;
    if (is_different(x4, w4)) pattern |= 1 << 12;
    if (is_different(x5, w4)) pattern |= 1 << 13;
    if (is_different(x6, w4)) pattern |= 1 << 14;

    int diagonal_bias = -7;
    while (pattern != 0) {
        diagonal_bias += pattern & 1;
        pattern >>= 1;
    }

    if (diagonal_bias <= 0) {
        vec4 r = mix(w1, w3, p.y - p.x + 0.5);
        if (dist < 0.5 - pixel_size / 2) {
            return r;
        }
        return mix(r, w4, (dist + pixel_size / 2 - 0.5) / pixel_size);
    }
    
    return w4;
}
