viewport-lib 0.12.1

/// Built-in colormap LUT data (256 RGBA samples each).
///
/// Each function returns a `[[u8; 4]; 256]` array suitable for uploading to a
/// 256×1 GPU texture.  All values are in linear (non-sRGB) space to match the
/// `Rgba8Unorm` texture format used by the LUT sampler.

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

#[inline]
fn clamp01(x: f32) -> f32 {
    x.clamp(0.0, 1.0)
}

#[inline]
fn to_u8(x: f32) -> u8 {
    (clamp01(x) * 255.0 + 0.5) as u8
}

// ---------------------------------------------------------------------------
// Greyscale: linear ramp black -> white
// ---------------------------------------------------------------------------

/// Linear greyscale ramp from black (index 0) to white (index 255).
pub fn greyscale_rgba() -> [[u8; 4]; 256] {
    let mut lut = [[0u8; 4]; 256];
    for i in 0..256 {
        let v = i as u8;
        lut[i] = [v, v, v, 255];
    }
    lut
}

// ---------------------------------------------------------------------------
// Viridis: Smith 2015 polynomial approximation
// ---------------------------------------------------------------------------

/// Viridis colormap : perceptually uniform, colorblind-friendly.
///
/// Uses the Smith 2015 polynomial approximation.
pub fn viridis_rgba() -> [[u8; 4]; 256] {
    let mut lut = [[0u8; 4]; 256];
    for i in 0..256 {
        let t = i as f32 / 255.0;
        // Degree-6 polynomial approximation (Zucker/Smith coefficients).
        // Range: dark purple (t=0) -> blue -> teal -> green -> yellow (t=1).
        let r = 0.277_727_33
            + t * (0.105_093_04
                + t * (-0.330_861_83
                    + t * (-4.634_230_5
                        + t * (6.228_269_9
                            + t * (4.776_385_0 - t * 5.435_455_9)))));
        let g = 0.005_407_345
            + t * (1.404_613_5
                + t * (0.214_847_56
                    + t * (-5.799_101_0
                        + t * (14.179_933
                            + t * (-13.745_145 + t * 4.645_852_6)))));
        let b = 0.334_099_81
            + t * (1.384_590_2
                + t * (0.095_095_16
                    + t * (-19.332_441
                        + t * (56.690_552
                            + t * (-65.353_033 + t * 26.312_435)))));
        lut[i] = [to_u8(r), to_u8(g), to_u8(b), 255];
    }
    lut
}

// ---------------------------------------------------------------------------
// Plasma: polynomial approximation
// ---------------------------------------------------------------------------

/// Plasma colormap : perceptually uniform, colorblind-friendly.
///
/// Uses a polynomial approximation of the Matplotlib plasma colormap.
pub fn plasma_rgba() -> [[u8; 4]; 256] {
    let mut lut = [[0u8; 4]; 256];
    for i in 0..256 {
        let t = i as f32 / 255.0;
        // Degree-6 polynomial approximation (Zucker/Kall coefficients).
        // Range: dark blue (t=0) -> pink (t=0.5) -> orange -> yellow (t=1).
        let r = 0.058_732_344
            + t * (2.176_514_6
                + t * (-2.689_460_5
                    + t * (6.130_348_3
                        + t * (-11.107_436
                            + t * (10.023_066 - t * 3.658_713_8)))));
        let g = 0.023_336_709
            + t * (0.238_383_42
                + t * (-7.455_851
                    + t * (42.346_188
                        + t * (-82.666_31
                            + t * (71.413_62 - t * 22.931_534)))));
        let b = 0.543_340_18
            + t * (0.753_960_46
                + t * (3.110_800
                    + t * (-28.518_854
                        + t * (60.139_847
                            + t * (-54.072_186 + t * 18.191_908)))));
        lut[i] = [to_u8(r), to_u8(g), to_u8(b), 255];
    }
    lut
}

// ---------------------------------------------------------------------------
// Coolwarm: diverging blue -> white -> red (cubic Hermite)
// ---------------------------------------------------------------------------

/// Diverging coolwarm colormap: blue at t=0, white at t=0.5, red at t=1.
pub fn coolwarm_rgba() -> [[u8; 4]; 256] {
    let mut lut = [[0u8; 4]; 256];

    // Control points in linear [0,1] space.
    let cold = [59.0 / 255.0_f32, 76.0 / 255.0, 192.0 / 255.0]; // blue
    let mid = [220.0 / 255.0_f32, 220.0 / 255.0, 220.0 / 255.0]; // near-white
    let warm = [180.0 / 255.0_f32, 4.0 / 255.0, 38.0 / 255.0]; // red

    for i in 0..256 {
        let t = i as f32 / 255.0;
        // Piecewise smooth cubic Hermite blend across two halves.
        let (r, g, b) = if t <= 0.5 {
            let s = t * 2.0; // [0,1] in the cold half
            let h = s * s * (3.0 - 2.0 * s); // smoothstep
            (
                cold[0] + h * (mid[0] - cold[0]),
                cold[1] + h * (mid[1] - cold[1]),
                cold[2] + h * (mid[2] - cold[2]),
            )
        } else {
            let s = (t - 0.5) * 2.0; // [0,1] in the warm half
            let h = s * s * (3.0 - 2.0 * s);
            (
                mid[0] + h * (warm[0] - mid[0]),
                mid[1] + h * (warm[1] - mid[1]),
                mid[2] + h * (warm[2] - mid[2]),
            )
        };
        lut[i] = [to_u8(r), to_u8(g), to_u8(b), 255];
    }
    lut
}

// ---------------------------------------------------------------------------
// Rainbow: HSV hue sweep 240° (blue) -> 0° (red) at full saturation/value
// ---------------------------------------------------------------------------

/// Rainbow colormap: HSV hue sweep from 240° (blue) at t=0 to 0° (red) at t=1.
pub fn rainbow_rgba() -> [[u8; 4]; 256] {
    let mut lut = [[0u8; 4]; 256];
    for i in 0..256 {
        let t = i as f32 / 255.0;
        // Hue sweeps from 240° down to 0° as t goes from 0 to 1.
        let hue = 240.0 * (1.0 - t); // degrees
        let (r, g, b) = hsv_to_rgb(hue, 1.0, 1.0);
        lut[i] = [to_u8(r), to_u8(g), to_u8(b), 255];
    }
    lut
}

/// Convert HSV (hue in degrees [0,360), saturation [0,1], value [0,1]) to RGB.
fn hsv_to_rgb(h: f32, s: f32, v: f32) -> (f32, f32, f32) {
    if s == 0.0 {
        return (v, v, v);
    }
    let h = h % 360.0;
    let sector = (h / 60.0).floor() as i32;
    let frac = h / 60.0 - sector as f32;
    let p = v * (1.0 - s);
    let q = v * (1.0 - s * frac);
    let t = v * (1.0 - s * (1.0 - frac));
    match sector {
        0 => (v, t, p),
        1 => (q, v, p),
        2 => (p, v, t),
        3 => (p, q, v),
        4 => (t, p, v),
        _ => (v, p, q),
    }
}

// ---------------------------------------------------------------------------
// Magma: exact 256-sample LUT sampled from matplotlib
// ---------------------------------------------------------------------------

/// Magma colormap : perceptually uniform. Black/purple -> orange -> near-white.
pub fn magma_rgba() -> [[u8; 4]; 256] {
    [
        [0,0,4,255], [1,0,5,255], [1,1,6,255], [1,1,8,255], [2,1,9,255], [2,2,11,255], [2,2,13,255], [3,3,15,255],
        [3,3,18,255], [4,4,20,255], [5,4,22,255], [6,5,24,255], [6,5,26,255], [7,6,28,255], [8,7,30,255], [9,7,32,255],
        [10,8,34,255], [11,9,36,255], [12,9,38,255], [13,10,41,255], [14,11,43,255], [16,11,45,255], [17,12,47,255], [18,13,49,255],
        [19,13,52,255], [20,14,54,255], [21,14,56,255], [22,15,59,255], [24,15,61,255], [25,16,63,255], [26,16,66,255], [28,16,68,255],
        [29,17,71,255], [30,17,73,255], [32,17,75,255], [33,17,78,255], [34,17,80,255], [36,18,83,255], [37,18,85,255], [39,18,88,255],
        [41,17,90,255], [42,17,92,255], [44,17,95,255], [45,17,97,255], [47,17,99,255], [49,17,101,255], [51,16,103,255], [52,16,105,255],
        [54,16,107,255], [56,16,108,255], [57,15,110,255], [59,15,112,255], [61,15,113,255], [63,15,114,255], [64,15,116,255], [66,15,117,255],
        [68,15,118,255], [69,16,119,255], [71,16,120,255], [73,16,120,255], [74,16,121,255], [76,17,122,255], [78,17,123,255], [79,18,123,255],
        [81,18,124,255], [82,19,124,255], [84,19,125,255], [86,20,125,255], [87,21,126,255], [89,21,126,255], [90,22,126,255], [92,22,127,255],
        [93,23,127,255], [95,24,127,255], [96,24,128,255], [98,25,128,255], [100,26,128,255], [101,26,128,255], [103,27,128,255], [104,28,129,255],
        [106,28,129,255], [107,29,129,255], [109,29,129,255], [110,30,129,255], [112,31,129,255], [114,31,129,255], [115,32,129,255], [117,33,129,255],
        [118,33,129,255], [120,34,129,255], [121,34,130,255], [123,35,130,255], [124,35,130,255], [126,36,130,255], [128,37,130,255], [129,37,129,255],
        [131,38,129,255], [132,38,129,255], [134,39,129,255], [136,39,129,255], [137,40,129,255], [139,41,129,255], [140,41,129,255], [142,42,129,255],
        [144,42,129,255], [145,43,129,255], [147,43,128,255], [148,44,128,255], [150,44,128,255], [152,45,128,255], [153,45,128,255], [155,46,127,255],
        [156,46,127,255], [158,47,127,255], [160,47,127,255], [161,48,126,255], [163,48,126,255], [165,49,126,255], [166,49,125,255], [168,50,125,255],
        [170,51,125,255], [171,51,124,255], [173,52,124,255], [174,52,123,255], [176,53,123,255], [178,53,123,255], [179,54,122,255], [181,54,122,255],
        [183,55,121,255], [184,55,121,255], [186,56,120,255], [188,57,120,255], [189,57,119,255], [191,58,119,255], [192,58,118,255], [194,59,117,255],
        [196,60,117,255], [197,60,116,255], [199,61,115,255], [200,62,115,255], [202,62,114,255], [204,63,113,255], [205,64,113,255], [207,64,112,255],
        [208,65,111,255], [210,66,111,255], [211,67,110,255], [213,68,109,255], [214,69,108,255], [216,69,108,255], [217,70,107,255], [219,71,106,255],
        [220,72,105,255], [222,73,104,255], [223,74,104,255], [224,76,103,255], [226,77,102,255], [227,78,101,255], [228,79,100,255], [229,80,100,255],
        [231,82,99,255], [232,83,98,255], [233,84,98,255], [234,86,97,255], [235,87,96,255], [236,88,96,255], [237,90,95,255], [238,91,94,255],
        [239,93,94,255], [240,95,94,255], [241,96,93,255], [242,98,93,255], [242,100,92,255], [243,101,92,255], [244,103,92,255], [244,105,92,255],
        [245,107,92,255], [246,108,92,255], [246,110,92,255], [247,112,92,255], [247,114,92,255], [248,116,92,255], [248,118,92,255], [249,120,93,255],
        [249,121,93,255], [249,123,93,255], [250,125,94,255], [250,127,94,255], [250,129,95,255], [251,131,95,255], [251,133,96,255], [251,135,97,255],
        [252,137,97,255], [252,138,98,255], [252,140,99,255], [252,142,100,255], [252,144,101,255], [253,146,102,255], [253,148,103,255], [253,150,104,255],
        [253,152,105,255], [253,154,106,255], [253,155,107,255], [254,157,108,255], [254,159,109,255], [254,161,110,255], [254,163,111,255], [254,165,113,255],
        [254,167,114,255], [254,169,115,255], [254,170,116,255], [254,172,118,255], [254,174,119,255], [254,176,120,255], [254,178,122,255], [254,180,123,255],
        [254,182,124,255], [254,183,126,255], [254,185,127,255], [254,187,129,255], [254,189,130,255], [254,191,132,255], [254,193,133,255], [254,194,135,255],
        [254,196,136,255], [254,198,138,255], [254,200,140,255], [254,202,141,255], [254,204,143,255], [254,205,144,255], [254,207,146,255], [254,209,148,255],
        [254,211,149,255], [254,213,151,255], [254,215,153,255], [254,216,154,255], [253,218,156,255], [253,220,158,255], [253,222,160,255], [253,224,161,255],
        [253,226,163,255], [253,227,165,255], [253,229,167,255], [253,231,169,255], [253,233,170,255], [253,235,172,255], [252,236,174,255], [252,238,176,255],
        [252,240,178,255], [252,242,180,255], [252,244,182,255], [252,246,184,255], [252,247,185,255], [252,249,187,255], [252,251,189,255], [252,253,191,255],
    ]
}

// ---------------------------------------------------------------------------
// Inferno: exact 256-sample LUT sampled from matplotlib
// ---------------------------------------------------------------------------

/// Inferno colormap : perceptually uniform. Black -> deep red -> orange -> light yellow.
pub fn inferno_rgba() -> [[u8; 4]; 256] {
    [
        [0,0,4,255], [1,0,5,255], [1,1,6,255], [1,1,8,255], [2,1,10,255], [2,2,12,255], [2,2,14,255], [3,2,16,255],
        [4,3,18,255], [4,3,20,255], [5,4,23,255], [6,4,25,255], [7,5,27,255], [8,5,29,255], [9,6,31,255], [10,7,34,255],
        [11,7,36,255], [12,8,38,255], [13,8,41,255], [14,9,43,255], [16,9,45,255], [17,10,48,255], [18,10,50,255], [20,11,52,255],
        [21,11,55,255], [22,11,57,255], [24,12,60,255], [25,12,62,255], [27,12,65,255], [28,12,67,255], [30,12,69,255], [31,12,72,255],
        [33,12,74,255], [35,12,76,255], [36,12,79,255], [38,12,81,255], [40,11,83,255], [41,11,85,255], [43,11,87,255], [45,11,89,255],
        [47,10,91,255], [49,10,92,255], [50,10,94,255], [52,10,95,255], [54,9,97,255], [56,9,98,255], [57,9,99,255], [59,9,100,255],
        [61,9,101,255], [62,9,102,255], [64,10,103,255], [66,10,104,255], [68,10,104,255], [69,10,105,255], [71,11,106,255], [73,11,106,255],
        [74,12,107,255], [76,12,107,255], [77,13,108,255], [79,13,108,255], [81,14,108,255], [82,14,109,255], [84,15,109,255], [85,15,109,255],
        [87,16,110,255], [89,16,110,255], [90,17,110,255], [92,18,110,255], [93,18,110,255], [95,19,110,255], [97,19,110,255], [98,20,110,255],
        [100,21,110,255], [101,21,110,255], [103,22,110,255], [105,22,110,255], [106,23,110,255], [108,24,110,255], [109,24,110,255], [111,25,110,255],
        [113,25,110,255], [114,26,110,255], [116,26,110,255], [117,27,110,255], [119,28,109,255], [120,28,109,255], [122,29,109,255], [124,29,109,255],
        [125,30,109,255], [127,30,108,255], [128,31,108,255], [130,32,108,255], [132,32,107,255], [133,33,107,255], [135,33,107,255], [136,34,106,255],
        [138,34,106,255], [140,35,105,255], [141,35,105,255], [143,36,105,255], [144,37,104,255], [146,37,104,255], [147,38,103,255], [149,38,103,255],
        [151,39,102,255], [152,39,102,255], [154,40,101,255], [155,41,100,255], [157,41,100,255], [159,42,99,255], [160,42,99,255], [162,43,98,255],
        [163,44,97,255], [165,44,96,255], [166,45,96,255], [168,46,95,255], [169,46,94,255], [171,47,94,255], [173,48,93,255], [174,48,92,255],
        [176,49,91,255], [177,50,90,255], [179,50,90,255], [180,51,89,255], [182,52,88,255], [183,53,87,255], [185,53,86,255], [186,54,85,255],
        [188,55,84,255], [189,56,83,255], [191,57,82,255], [192,58,81,255], [193,58,80,255], [195,59,79,255], [196,60,78,255], [198,61,77,255],
        [199,62,76,255], [200,63,75,255], [202,64,74,255], [203,65,73,255], [204,66,72,255], [206,67,71,255], [207,68,70,255], [208,69,69,255],
        [210,70,68,255], [211,71,67,255], [212,72,66,255], [213,74,65,255], [215,75,63,255], [216,76,62,255], [217,77,61,255], [218,78,60,255],
        [219,80,59,255], [221,81,58,255], [222,82,56,255], [223,83,55,255], [224,85,54,255], [225,86,53,255], [226,87,52,255], [227,89,51,255],
        [228,90,49,255], [229,92,48,255], [230,93,47,255], [231,94,46,255], [232,96,45,255], [233,97,43,255], [234,99,42,255], [235,100,41,255],
        [235,102,40,255], [236,103,38,255], [237,105,37,255], [238,106,36,255], [239,108,35,255], [239,110,33,255], [240,111,32,255], [241,113,31,255],
        [241,115,29,255], [242,116,28,255], [243,118,27,255], [243,120,25,255], [244,121,24,255], [245,123,23,255], [245,125,21,255], [246,126,20,255],
        [246,128,19,255], [247,130,18,255], [247,132,16,255], [248,133,15,255], [248,135,14,255], [248,137,12,255], [249,139,11,255], [249,140,10,255],
        [249,142,9,255], [250,144,8,255], [250,146,7,255], [250,148,7,255], [251,150,6,255], [251,151,6,255], [251,153,6,255], [251,155,6,255],
        [251,157,7,255], [252,159,7,255], [252,161,8,255], [252,163,9,255], [252,165,10,255], [252,166,12,255], [252,168,13,255], [252,170,15,255],
        [252,172,17,255], [252,174,18,255], [252,176,20,255], [252,178,22,255], [252,180,24,255], [251,182,26,255], [251,184,29,255], [251,186,31,255],
        [251,188,33,255], [251,190,35,255], [250,192,38,255], [250,194,40,255], [250,196,42,255], [250,198,45,255], [249,199,47,255], [249,201,50,255],
        [249,203,53,255], [248,205,55,255], [248,207,58,255], [247,209,61,255], [247,211,64,255], [246,213,67,255], [246,215,70,255], [245,217,73,255],
        [245,219,76,255], [244,221,79,255], [244,223,83,255], [244,225,86,255], [243,227,90,255], [243,229,93,255], [242,230,97,255], [242,232,101,255],
        [242,234,105,255], [241,236,109,255], [241,237,113,255], [241,239,117,255], [241,241,121,255], [242,242,125,255], [242,244,130,255], [243,245,134,255],
        [243,246,138,255], [244,248,142,255], [245,249,146,255], [246,250,150,255], [248,251,154,255], [249,252,157,255], [250,253,161,255], [252,255,164,255],
    ]
}

// ---------------------------------------------------------------------------
// Turbo: exact 256-sample LUT sampled from matplotlib
// ---------------------------------------------------------------------------

/// Turbo colormap (Google 2019) : improved rainbow. Deep purple -> cyan -> green -> yellow -> red.
pub fn turbo_rgba() -> [[u8; 4]; 256] {
    [
        [48,18,59,255], [50,21,67,255], [51,24,74,255], [52,27,81,255], [53,30,88,255], [54,33,95,255], [55,36,102,255], [56,39,109,255],
        [57,42,115,255], [58,45,121,255], [59,47,128,255], [60,50,134,255], [61,53,139,255], [62,56,145,255], [63,59,151,255], [63,62,156,255],
        [64,64,162,255], [65,67,167,255], [65,70,172,255], [66,73,177,255], [66,75,181,255], [67,78,186,255], [68,81,191,255], [68,84,195,255],
        [68,86,199,255], [69,89,203,255], [69,92,207,255], [69,94,211,255], [70,97,214,255], [70,100,218,255], [70,102,221,255], [70,105,224,255],
        [70,107,227,255], [71,110,230,255], [71,113,233,255], [71,115,235,255], [71,118,238,255], [71,120,240,255], [71,123,242,255], [70,125,244,255],
        [70,128,246,255], [70,130,248,255], [70,133,250,255], [70,135,251,255], [69,138,252,255], [69,140,253,255], [68,143,254,255], [67,145,254,255],
        [66,148,255,255], [65,150,255,255], [64,153,255,255], [62,155,254,255], [61,158,254,255], [59,160,253,255], [58,163,252,255], [56,165,251,255],
        [55,168,250,255], [53,171,248,255], [51,173,247,255], [49,175,245,255], [47,178,244,255], [46,180,242,255], [44,183,240,255], [42,185,238,255],
        [40,188,235,255], [39,190,233,255], [37,192,231,255], [35,195,228,255], [34,197,226,255], [32,199,223,255], [31,201,221,255], [30,203,218,255],
        [28,205,216,255], [27,208,213,255], [26,210,210,255], [26,212,208,255], [25,213,205,255], [24,215,202,255], [24,217,200,255], [24,219,197,255],
        [24,221,194,255], [24,222,192,255], [24,224,189,255], [25,226,187,255], [25,227,185,255], [26,228,182,255], [28,230,180,255], [29,231,178,255],
        [31,233,175,255], [32,234,172,255], [34,235,170,255], [37,236,167,255], [39,238,164,255], [42,239,161,255], [44,240,158,255], [47,241,155,255],
        [50,242,152,255], [53,243,148,255], [56,244,145,255], [60,245,142,255], [63,246,138,255], [67,247,135,255], [70,248,132,255], [74,248,128,255],
        [78,249,125,255], [82,250,122,255], [85,250,118,255], [89,251,115,255], [93,252,111,255], [97,252,108,255], [101,253,105,255], [105,253,102,255],
        [109,254,98,255], [113,254,95,255], [117,254,92,255], [121,254,89,255], [125,255,86,255], [128,255,83,255], [132,255,81,255], [136,255,78,255],
        [139,255,75,255], [143,255,73,255], [146,255,71,255], [150,254,68,255], [153,254,66,255], [156,254,64,255], [159,253,63,255], [161,253,61,255],
        [164,252,60,255], [167,252,58,255], [169,251,57,255], [172,251,56,255], [175,250,55,255], [177,249,54,255], [180,248,54,255], [183,247,53,255],
        [185,246,53,255], [188,245,52,255], [190,244,52,255], [193,243,52,255], [195,241,52,255], [198,240,52,255], [200,239,52,255], [203,237,52,255],
        [205,236,52,255], [208,234,52,255], [210,233,53,255], [212,231,53,255], [215,229,53,255], [217,228,54,255], [219,226,54,255], [221,224,55,255],
        [223,223,55,255], [225,221,55,255], [227,219,56,255], [229,217,56,255], [231,215,57,255], [233,213,57,255], [235,211,57,255], [236,209,58,255],
        [238,207,58,255], [239,205,58,255], [241,203,58,255], [242,201,58,255], [244,199,58,255], [245,197,58,255], [246,195,58,255], [247,193,58,255],
        [248,190,57,255], [249,188,57,255], [250,186,57,255], [251,184,56,255], [251,182,55,255], [252,179,54,255], [252,177,54,255], [253,174,53,255],
        [253,172,52,255], [254,169,51,255], [254,167,50,255], [254,164,49,255], [254,161,48,255], [254,158,47,255], [254,155,45,255], [254,153,44,255],
        [254,150,43,255], [254,147,42,255], [254,144,41,255], [253,141,39,255], [253,138,38,255], [252,135,37,255], [252,132,35,255], [251,129,34,255],
        [251,126,33,255], [250,123,31,255], [249,120,30,255], [249,117,29,255], [248,114,28,255], [247,111,26,255], [246,108,25,255], [245,105,24,255],
        [244,102,23,255], [243,99,21,255], [242,96,20,255], [241,93,19,255], [240,91,18,255], [239,88,17,255], [237,85,16,255], [236,83,15,255],
        [235,80,14,255], [234,78,13,255], [232,75,12,255], [231,73,12,255], [229,71,11,255], [228,69,10,255], [226,67,10,255], [225,65,9,255],
        [223,63,8,255], [221,61,8,255], [220,59,7,255], [218,57,7,255], [216,55,6,255], [214,53,6,255], [212,51,5,255], [210,49,5,255],
        [208,47,5,255], [206,45,4,255], [204,43,4,255], [202,42,4,255], [200,40,3,255], [197,38,3,255], [195,37,3,255], [193,35,2,255],
        [190,33,2,255], [188,32,2,255], [185,30,2,255], [183,29,2,255], [180,27,1,255], [178,26,1,255], [175,24,1,255], [172,23,1,255],
        [169,22,1,255], [167,20,1,255], [164,19,1,255], [161,18,1,255], [158,16,1,255], [155,15,1,255], [152,14,1,255], [149,13,1,255],
        [146,11,1,255], [142,10,1,255], [139,9,2,255], [136,8,2,255], [133,7,2,255], [129,6,2,255], [126,5,2,255], [122,4,3,255],
    ]
}

// ---------------------------------------------------------------------------
// Jet: exact 256-sample LUT sampled from matplotlib
// ---------------------------------------------------------------------------

/// Jet colormap : classic blue-cyan-green-yellow-red. Not perceptually uniform.
pub fn jet_rgba() -> [[u8; 4]; 256] {
    [
        [0,0,128,255], [0,0,132,255], [0,0,137,255], [0,0,141,255], [0,0,146,255], [0,0,150,255], [0,0,155,255], [0,0,159,255],
        [0,0,164,255], [0,0,168,255], [0,0,173,255], [0,0,178,255], [0,0,182,255], [0,0,187,255], [0,0,191,255], [0,0,196,255],
        [0,0,200,255], [0,0,205,255], [0,0,209,255], [0,0,214,255], [0,0,218,255], [0,0,223,255], [0,0,227,255], [0,0,232,255],
        [0,0,237,255], [0,0,241,255], [0,0,246,255], [0,0,250,255], [0,0,255,255], [0,0,255,255], [0,0,255,255], [0,0,255,255],
        [0,1,255,255], [0,4,255,255], [0,9,255,255], [0,13,255,255], [0,17,255,255], [0,20,255,255], [0,25,255,255], [0,29,255,255],
        [0,33,255,255], [0,36,255,255], [0,41,255,255], [0,45,255,255], [0,49,255,255], [0,52,255,255], [0,57,255,255], [0,61,255,255],
        [0,65,255,255], [0,68,255,255], [0,73,255,255], [0,77,255,255], [0,81,255,255], [0,84,255,255], [0,89,255,255], [0,93,255,255],
        [0,97,255,255], [0,100,255,255], [0,105,255,255], [0,109,255,255], [0,113,255,255], [0,116,255,255], [0,121,255,255], [0,125,255,255],
        [0,129,255,255], [0,133,255,255], [0,136,255,255], [0,141,255,255], [0,145,255,255], [0,149,255,255], [0,153,255,255], [0,157,255,255],
        [0,161,255,255], [0,165,255,255], [0,168,255,255], [0,173,255,255], [0,177,255,255], [0,181,255,255], [0,185,255,255], [0,189,255,255],
        [0,193,255,255], [0,197,255,255], [0,200,255,255], [0,205,255,255], [0,209,255,255], [0,213,255,255], [0,217,255,255], [0,221,254,255],
        [0,225,251,255], [0,229,248,255], [2,232,244,255], [6,237,241,255], [9,241,238,255], [12,245,235,255], [15,249,231,255], [19,253,228,255],
        [22,255,225,255], [25,255,222,255], [28,255,219,255], [31,255,215,255], [35,255,212,255], [38,255,209,255], [41,255,206,255], [44,255,202,255],
        [48,255,199,255], [51,255,196,255], [54,255,193,255], [57,255,190,255], [60,255,186,255], [64,255,183,255], [67,255,180,255], [70,255,177,255],
        [73,255,173,255], [77,255,170,255], [80,255,167,255], [83,255,164,255], [86,255,160,255], [90,255,157,255], [93,255,154,255], [96,255,151,255],
        [99,255,148,255], [102,255,144,255], [106,255,141,255], [109,255,138,255], [112,255,135,255], [115,255,131,255], [119,255,128,255], [122,255,125,255],
        [125,255,122,255], [128,255,119,255], [131,255,115,255], [135,255,112,255], [138,255,109,255], [141,255,106,255], [144,255,102,255], [148,255,99,255],
        [151,255,96,255], [154,255,93,255], [157,255,90,255], [160,255,86,255], [164,255,83,255], [167,255,80,255], [170,255,77,255], [173,255,73,255],
        [177,255,70,255], [180,255,67,255], [183,255,64,255], [186,255,60,255], [190,255,57,255], [193,255,54,255], [196,255,51,255], [199,255,48,255],
        [202,255,44,255], [206,255,41,255], [209,255,38,255], [212,255,35,255], [215,255,31,255], [219,255,28,255], [222,255,25,255], [225,255,22,255],
        [228,255,19,255], [231,255,15,255], [235,255,12,255], [238,255,9,255], [241,252,6,255], [244,248,2,255], [248,245,0,255], [251,241,0,255],
        [254,237,0,255], [255,234,0,255], [255,230,0,255], [255,226,0,255], [255,222,0,255], [255,219,0,255], [255,215,0,255], [255,211,0,255],
        [255,208,0,255], [255,204,0,255], [255,200,0,255], [255,196,0,255], [255,193,0,255], [255,189,0,255], [255,185,0,255], [255,182,0,255],
        [255,178,0,255], [255,174,0,255], [255,171,0,255], [255,167,0,255], [255,163,0,255], [255,159,0,255], [255,156,0,255], [255,152,0,255],
        [255,148,0,255], [255,145,0,255], [255,141,0,255], [255,137,0,255], [255,134,0,255], [255,130,0,255], [255,126,0,255], [255,122,0,255],
        [255,119,0,255], [255,115,0,255], [255,111,0,255], [255,108,0,255], [255,104,0,255], [255,100,0,255], [255,96,0,255], [255,93,0,255],
        [255,89,0,255], [255,85,0,255], [255,82,0,255], [255,78,0,255], [255,74,0,255], [255,71,0,255], [255,67,0,255], [255,63,0,255],
        [255,59,0,255], [255,56,0,255], [255,52,0,255], [255,48,0,255], [255,45,0,255], [255,41,0,255], [255,37,0,255], [255,34,0,255],
        [255,30,0,255], [255,26,0,255], [255,22,0,255], [255,19,0,255], [250,15,0,255], [246,11,0,255], [241,8,0,255], [237,4,0,255],
        [232,0,0,255], [228,0,0,255], [223,0,0,255], [218,0,0,255], [214,0,0,255], [209,0,0,255], [205,0,0,255], [200,0,0,255],
        [196,0,0,255], [191,0,0,255], [187,0,0,255], [182,0,0,255], [178,0,0,255], [173,0,0,255], [168,0,0,255], [164,0,0,255],
        [159,0,0,255], [155,0,0,255], [150,0,0,255], [146,0,0,255], [141,0,0,255], [137,0,0,255], [132,0,0,255], [128,0,0,255],
    ]
}

// ---------------------------------------------------------------------------
// RdBu (reversed): exact 256-sample LUT sampled from matplotlib
// ---------------------------------------------------------------------------

/// RdBu diverging colormap (red -> white -> blue, reversed so blue is at t=0).
/// Suitable for signed quantities (negative = blue, zero = white, positive = red).
pub fn rdbu_r_rgba() -> [[u8; 4]; 256] {
    [
        [5,48,97,255], [6,50,100,255], [7,52,103,255], [8,54,106,255], [9,56,109,255], [10,59,112,255], [12,61,115,255], [13,63,118,255],
        [14,65,121,255], [15,67,123,255], [16,69,126,255], [17,71,129,255], [18,73,132,255], [19,76,135,255], [20,78,138,255], [21,80,141,255],
        [23,82,144,255], [24,84,147,255], [25,86,150,255], [26,88,153,255], [27,90,156,255], [28,92,159,255], [29,95,162,255], [30,97,165,255],
        [31,99,168,255], [32,101,171,255], [34,103,172,255], [35,105,173,255], [36,106,174,255], [38,108,175,255], [39,110,176,255], [40,112,177,255],
        [42,113,178,255], [43,115,179,255], [44,117,180,255], [46,119,181,255], [47,121,181,255], [48,122,182,255], [50,124,183,255], [51,126,184,255],
        [52,128,185,255], [54,129,186,255], [55,131,187,255], [56,133,188,255], [58,135,189,255], [59,136,190,255], [60,138,190,255], [62,140,191,255],
        [63,142,192,255], [64,143,193,255], [66,145,194,255], [67,147,195,255], [70,149,196,255], [73,151,197,255], [76,153,198,255], [79,155,199,255],
        [82,157,200,255], [86,159,201,255], [89,161,202,255], [92,163,203,255], [95,165,205,255], [98,167,206,255], [101,169,207,255], [104,171,208,255],
        [107,172,209,255], [110,174,210,255], [113,176,211,255], [117,178,212,255], [120,180,213,255], [123,182,214,255], [126,184,215,255], [129,186,216,255],
        [132,188,217,255], [135,190,218,255], [138,192,219,255], [141,194,220,255], [144,196,221,255], [147,198,222,255], [150,199,223,255], [152,200,224,255],
        [155,201,224,255], [157,203,225,255], [160,204,226,255], [162,205,227,255], [165,206,227,255], [167,208,228,255], [169,209,229,255], [172,210,229,255],
        [174,211,230,255], [177,213,231,255], [179,214,232,255], [182,215,232,255], [184,216,233,255], [187,218,234,255], [189,219,234,255], [192,220,235,255],
        [194,221,236,255], [197,223,236,255], [199,224,237,255], [202,225,238,255], [204,226,239,255], [207,228,239,255], [209,229,240,255], [210,230,240,255],
        [212,230,241,255], [213,231,241,255], [215,232,241,255], [216,233,241,255], [218,233,242,255], [219,234,242,255], [221,235,242,255], [222,235,242,255],
        [224,236,243,255], [225,237,243,255], [227,237,243,255], [228,238,244,255], [230,239,244,255], [231,240,244,255], [233,240,244,255], [234,241,245,255],
        [236,242,245,255], [237,242,245,255], [239,243,245,255], [240,244,246,255], [242,245,246,255], [243,245,246,255], [245,246,247,255], [246,247,247,255],
        [247,246,246,255], [247,245,244,255], [248,244,242,255], [248,243,240,255], [248,242,239,255], [248,241,237,255], [249,240,235,255], [249,239,233,255],
        [249,238,231,255], [249,237,229,255], [249,235,227,255], [250,234,225,255], [250,233,223,255], [250,232,222,255], [250,231,220,255], [251,230,218,255],
        [251,229,216,255], [251,228,214,255], [251,227,212,255], [252,226,210,255], [252,224,208,255], [252,223,207,255], [252,222,205,255], [253,221,203,255],
        [253,220,201,255], [253,219,199,255], [253,217,196,255], [252,215,194,255], [252,213,191,255], [252,211,188,255], [251,208,185,255], [251,206,183,255],
        [251,204,180,255], [250,202,177,255], [250,200,175,255], [249,198,172,255], [249,196,169,255], [249,194,167,255], [248,191,164,255], [248,189,161,255],
        [248,187,158,255], [247,185,156,255], [247,183,153,255], [247,181,150,255], [246,179,148,255], [246,177,145,255], [246,175,142,255], [245,172,139,255],
        [245,170,137,255], [245,168,134,255], [244,166,131,255], [243,164,129,255], [242,161,127,255], [241,158,125,255], [240,156,123,255], [239,153,121,255],
        [238,150,119,255], [236,147,116,255], [235,145,114,255], [234,142,112,255], [233,139,110,255], [232,137,108,255], [230,134,106,255], [229,131,104,255],
        [228,128,102,255], [227,126,100,255], [226,123,98,255], [225,120,96,255], [223,118,94,255], [222,115,92,255], [221,112,89,255], [220,110,87,255],
        [219,107,85,255], [218,104,83,255], [216,101,81,255], [215,99,79,255], [214,96,77,255], [213,93,76,255], [211,90,74,255], [210,88,73,255],
        [208,85,72,255], [207,82,70,255], [206,79,69,255], [204,76,68,255], [203,73,66,255], [201,71,65,255], [200,68,64,255], [198,65,62,255],
        [197,62,61,255], [196,59,60,255], [194,56,58,255], [193,54,57,255], [191,51,56,255], [190,48,54,255], [189,45,53,255], [187,42,52,255],
        [186,40,50,255], [184,37,49,255], [183,34,48,255], [182,31,46,255], [180,28,45,255], [179,25,44,255], [177,24,43,255], [174,23,42,255],
        [171,22,42,255], [168,21,41,255], [165,20,41,255], [162,19,40,255], [159,18,40,255], [156,17,39,255], [153,16,39,255], [150,15,39,255],
        [147,14,38,255], [144,13,38,255], [141,12,37,255], [138,11,37,255], [135,10,36,255], [132,9,36,255], [129,8,35,255], [127,8,35,255],
        [124,7,34,255], [121,6,34,255], [118,5,33,255], [115,4,33,255], [112,3,32,255], [109,2,32,255], [106,1,31,255], [103,0,31,255],
    ]
}

// ---------------------------------------------------------------------------
// Custom colormap LUT generation
// ---------------------------------------------------------------------------

/// Linearly interpolate between colour stops to produce a 256-sample LUT.
///
/// `stops` is a slice of `(position, rgba)` pairs where `position` is in `[0, 1]`.
/// Stops are sorted by position before interpolation.
/// The result is clamped: the first stop colour fills `t < stops[0].0` and the last
/// stop colour fills `t > stops.last().0`.
///
/// Returns a `[[u8; 4]; 256]` suitable for uploading to a 256×1 GPU texture.
pub fn lerp_colormap_lut(stops: &[(f32, [u8; 4])]) -> [[u8; 4]; 256] {
    let mut lut = [[0u8; 4]; 256];
    if stops.is_empty() {
        return lut;
    }
    // Sort by position.
    let mut sorted: Vec<(f32, [u8; 4])> = stops.to_vec();
    sorted.sort_by(|a, b| a.0.partial_cmp(&b.0).unwrap_or(std::cmp::Ordering::Equal));

    for i in 0..256 {
        let t = i as f32 / 255.0;

        // Find the surrounding stops.
        let first = sorted[0];
        let last = *sorted.last().unwrap();

        if t <= first.0 {
            lut[i] = first.1;
            continue;
        }
        if t >= last.0 {
            lut[i] = last.1;
            continue;
        }

        // Binary search for the lower stop.
        let pos = sorted.partition_point(|s| s.0 <= t);
        let lo = sorted[pos - 1];
        let hi = sorted[pos];

        let range = hi.0 - lo.0;
        let frac = if range > 1.0e-7 {
            (t - lo.0) / range
        } else {
            0.0
        };
        lut[i] = [
            (lo.1[0] as f32 + (hi.1[0] as f32 - lo.1[0] as f32) * frac + 0.5) as u8,
            (lo.1[1] as f32 + (hi.1[1] as f32 - lo.1[1] as f32) * frac + 0.5) as u8,
            (lo.1[2] as f32 + (hi.1[2] as f32 - lo.1[2] as f32) * frac + 0.5) as u8,
            (lo.1[3] as f32 + (hi.1[3] as f32 - lo.1[3] as f32) * frac + 0.5) as u8,
        ];
    }
    lut
}

/// Parse a ParaView XML colormap file.
///
/// Supports the standard format:
/// ```xml
/// <ColorMaps>
///   <ColorMap name="MyMap" space="RGB">
///     <Point x="0.0" r="0.0" g="0.0" b="0.0" o="1.0"/>
///     <Point x="1.0" r="1.0" g="1.0" b="1.0" o="1.0"/>
///   </ColorMap>
/// </ColorMaps>
/// ```
///
/// Returns a list of `(name, stops)` pairs, where each stop is `(position_0_1, [r, g, b, a])`.
/// Uses simple string parsing without any XML library dependency.
pub fn parse_paraview_xml_colormap(xml: &str) -> Vec<(String, Vec<(f32, [u8; 4])>)> {
    let mut result = Vec::new();
    let mut current_name: Option<String> = None;
    let mut current_stops: Vec<(f32, [u8; 4])> = Vec::new();

    for line in xml.lines() {
        let trimmed = line.trim();

        if trimmed.starts_with("<ColorMap") {
            // Extract name attribute.
            current_name = attr_value(trimmed, "name").map(|s| s.to_string());
            current_stops.clear();
        } else if trimmed.starts_with("</ColorMap>") {
            if let Some(name) = current_name.take() {
                if !current_stops.is_empty() {
                    result.push((name, current_stops.clone()));
                }
            }
            current_stops.clear();
        } else if trimmed.starts_with("<Point") {
            // Parse x, r, g, b, o attributes.
            if let (Some(x), Some(r), Some(g), Some(b)) = (
                attr_f32(trimmed, "x"),
                attr_f32(trimmed, "r"),
                attr_f32(trimmed, "g"),
                attr_f32(trimmed, "b"),
            ) {
                let a = attr_f32(trimmed, "o").unwrap_or(1.0);
                let stop = (
                    x,
                    [
                        (r.clamp(0.0, 1.0) * 255.0 + 0.5) as u8,
                        (g.clamp(0.0, 1.0) * 255.0 + 0.5) as u8,
                        (b.clamp(0.0, 1.0) * 255.0 + 0.5) as u8,
                        (a.clamp(0.0, 1.0) * 255.0 + 0.5) as u8,
                    ],
                );
                current_stops.push(stop);
            }
        }
    }

    result
}

/// Serialize a colormap to the ParaView XML colormap format.
pub fn export_paraview_xml_colormap(name: &str, stops: &[(f32, [u8; 4])]) -> String {
    let mut out = String::new();
    out.push_str("<ColorMaps>\n");
    out.push_str(&format!("  <ColorMap name=\"{}\" space=\"RGB\">\n", name));
    for &(pos, rgba) in stops {
        let r = rgba[0] as f32 / 255.0;
        let g = rgba[1] as f32 / 255.0;
        let b = rgba[2] as f32 / 255.0;
        let o = rgba[3] as f32 / 255.0;
        out.push_str(&format!(
            "    <Point x=\"{:.6}\" r=\"{:.6}\" g=\"{:.6}\" b=\"{:.6}\" o=\"{:.6}\"/>\n",
            pos, r, g, b, o
        ));
    }
    out.push_str("  </ColorMap>\n");
    out.push_str("</ColorMaps>\n");
    out
}

// ---------------------------------------------------------------------------
// XML parsing helpers
// ---------------------------------------------------------------------------

/// Extract the string value of a named XML attribute from a tag line.
/// e.g. `attr_value(r#"<Point x="0.5"/>"#, "x")` returns `Some("0.5")`.
fn attr_value<'a>(tag: &'a str, name: &str) -> Option<&'a str> {
    let search = format!("{}=\"", name);
    let start = tag.find(search.as_str())? + search.len();
    let end = tag[start..].find('"')? + start;
    Some(&tag[start..end])
}

fn attr_f32(tag: &str, name: &str) -> Option<f32> {
    attr_value(tag, name)?.parse().ok()
}