transfer.cpp.hpp

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// ok no header - implementation for fl/gfx/transfer.h
 
#include "fl/gfx/transfer.h"
 
#include "fastled_progmem.h"
#include "fl/stl/align.h"
 
namespace fl {
 
// Inverse sRGB transfer, 8-bit code -> u16 linear.
// Generated by: round(f(i / 255.0) * 65535.0) for i in 0..255, where
//   f(n) = n / 12.92                        if n <= 0.04045
//        = ((n + 0.055) / 1.055) ** 2.4     otherwise
// This is the piecewise sRGB function, not the BT.709 OETF -- the spec keeps
// them distinct, and the two differ by more than a rounding step at low codes
// (code 1 decodes to 20 here and 57 under BT.709). Matches the P5 float64
// reference `ci/color_reference.py::decode_rgb8` by construction; a Python
// test regenerates this table and fails on any drift.
FL_ALIGN_PROGMEM(64) const u16 SRGB_DECODE_LUT[256] FL_PROGMEM = {
        0,    20,    40,    60,    80,    99,   119,   139,   159,   179,
      199,   219,   241,   264,   288,   313,   340,   367,   396,   427,
      458,   491,   526,   562,   599,   637,   677,   718,   761,   805,
      851,   898,   947,   997,  1048,  1101,  1156,  1212,  1270,  1330,
     1391,  1453,  1517,  1583,  1651,  1720,  1790,  1863,  1937,  2013,
     2090,  2170,  2250,  2333,  2418,  2504,  2592,  2681,  2773,  2866,
     2961,  3058,  3157,  3258,  3360,  3464,  3570,  3678,  3788,  3900,
     4014,  4129,  4247,  4366,  4488,  4611,  4736,  4864,  4993,  5124,
     5257,  5392,  5530,  5669,  5810,  5953,  6099,  6246,  6395,  6547,
     6700,  6856,  7014,  7174,  7335,  7500,  7666,  7834,  8004,  8177,
     8352,  8528,  8708,  8889,  9072,  9258,  9445,  9635,  9828, 10022,
    10219, 10417, 10619, 10822, 11028, 11235, 11446, 11658, 11873, 12090,
    12309, 12530, 12754, 12980, 13209, 13440, 13673, 13909, 14146, 14387,
    14629, 14874, 15122, 15371, 15623, 15878, 16135, 16394, 16656, 16920,
    17187, 17456, 17727, 18001, 18277, 18556, 18837, 19121, 19407, 19696,
    19987, 20281, 20577, 20876, 21177, 21481, 21787, 22096, 22407, 22721,
    23038, 23357, 23678, 24002, 24329, 24658, 24990, 25325, 25662, 26001,
    26344, 26688, 27036, 27386, 27739, 28094, 28452, 28813, 29176, 29542,
    29911, 30282, 30656, 31033, 31412, 31794, 32179, 32567, 32957, 33350,
    33745, 34143, 34544, 34948, 35355, 35764, 36176, 36591, 37008, 37429,
    37852, 38278, 38706, 39138, 39572, 40009, 40449, 40891, 41337, 41785,
    42236, 42690, 43147, 43606, 44069, 44534, 45002, 45473, 45947, 46423,
    46903, 47385, 47871, 48359, 48850, 49344, 49841, 50341, 50844, 51349,
    51858, 52369, 52884, 53401, 53921, 54445, 54971, 55500, 56032, 56567,
    57105, 57646, 58190, 58737, 59287, 59840, 60396, 60955, 61517, 62082,
    62650, 63221, 63795, 64372, 64952, 65535};
 
// Inverse BT.709 transfer, 8-bit code -> u16 linear.
// Generated by: round(f(i / 255.0) * 65535.0) for i in 0..255, where
//   f(n) = n / 4.5                             if n < 0.081
//        = ((n + 0.099) / 1.099) ** (1 / 0.45) otherwise
FL_ALIGN_PROGMEM(64) const u16 BT709_DECODE_LUT[256] FL_PROGMEM = {
        0,    57,   114,   171,   228,   286,   343,   400,   457,   514,
      571,   628,   685,   742,   800,   857,   914,   971,  1028,  1085,
     1142,  1196,  1254,  1314,  1375,  1438,  1502,  1568,  1636,  1705,
     1775,  1847,  1921,  1997,  2074,  2152,  2232,  2314,  2398,  2483,
     2569,  2658,  2748,  2839,  2933,  3028,  3124,  3222,  3322,  3424,
     3527,  3632,  3739,  3848,  3958,  4069,  4183,  4298,  4415,  4534,
     4655,  4777,  4901,  5026,  5154,  5283,  5414,  5547,  5681,  5818,
     5956,  6095,  6237,  6381,  6526,  6673,  6822,  6972,  7125,  7279,
     7435,  7593,  7753,  7914,  8078,  8243,  8410,  8579,  8750,  8922,
     9097,  9273,  9451,  9631,  9813,  9997, 10183, 10370, 10560, 10751,
    10944, 11139, 11337, 11535, 11736, 11939, 12144, 12350, 12559, 12769,
    12982, 13196, 13412, 13630, 13850, 14072, 14296, 14522, 14750, 14980,
    15211, 15445, 15681, 15918, 16158, 16400, 16643, 16889, 17136, 17386,
    17637, 17891, 18146, 18403, 18663, 18924, 19188, 19453, 19721, 19990,
    20262, 20535, 20811, 21088, 21368, 21649, 21933, 22219, 22506, 22796,
    23088, 23381, 23677, 23975, 24275, 24577, 24881, 25187, 25495, 25806,
    26118, 26432, 26749, 27067, 27388, 27710, 28035, 28362, 28691, 29022,
    29355, 29690, 30027, 30366, 30708, 31051, 31397, 31745, 32095, 32447,
    32801, 33157, 33515, 33876, 34238, 34603, 34970, 35339, 35710, 36083,
    36458, 36836, 37215, 37597, 37981, 38367, 38755, 39146, 39538, 39933,
    40329, 40728, 41130, 41533, 41938, 42346, 42756, 43168, 43582, 43998,
    44417, 44837, 45260, 45685, 46112, 46542, 46973, 47407, 47843, 48281,
    48722, 49164, 49609, 50056, 50505, 50957, 51410, 51866, 52324, 52784,
    53247, 53712, 54178, 54648, 55119, 55593, 56068, 56546, 57027, 57509,
    57994, 58481, 58970, 59462, 59955, 60451, 60950, 61450, 61953, 62458,
    62965, 63474, 63986, 64500, 65016, 65535};
 
u16 decodeTransferU16(TransferFunction transfer, u8 code) FL_NO_EXCEPT {
    switch (transfer) {
    case TransferFunction::Srgb:
        return FL_PGM_READ_WORD_ALIGNED(&SRGB_DECODE_LUT[code]);
    case TransferFunction::Bt709:
        return FL_PGM_READ_WORD_ALIGNED(&BT709_DECODE_LUT[code]);
    case TransferFunction::Linear:
        break;
    }
    // Linear needs no table: 257 maps 0..255 onto 0..65535 exactly, so 0 and
    // 255 land on the endpoints without a rounding step.
    return static_cast<u16>(static_cast<u32>(code) * 257u);
}
 
}  // namespace fl