store_as_bmp.cpp

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// Q'N'D code.

#include <ctype.h>
// w:173; h:111 bpp:24; bppl = 3; actual_w = 176; bytes_per_pixel = 3
// b - bitmap, w - width, h - height, bpp - bits per pixel, p - RGB palette
static void store_as_bmp(char * fn,
    const H3R_NS::byte * b, int w, int h, int bpp, const H3R_NS::byte * p)
{
    int bytes_per_pixel {bpp >> 3};
    int bpl = w *  bytes_per_pixel;
    int bbpl {(4 - (bpl % 4)) & 3}; // bonus bytes per line
                                    // "BMP" format requirement
    H3R_NS::byte h8[] = {
        0x42, 0x4d,      //  0
        0, 0, 0, 0,      //  2
        0, 0, 0, 0,      //  6
        0, 0, 0, 0,      // 10
        0x28, 0, 0, 0,   // 14
        0, 0, 0, 0,      // 18
        0, 0, 0, 0,      // 22
        1, 0,            // 26
        0, 0,            // 28
        0, 0, 0, 0,      // 30
        0, 0, 0, 0,      // 34
        0x13, 0x0b, 0, 0,// 38
        0x13, 0x0b, 0, 0,// 42
        0, 0, 0, 0,      // 46
        0, 0, 0, 0       // 50
    };
    const int FSIZE {2}, BMPOFS {10}, W {18}, H {22}, BPP {28}, BMPSIZE {34},
        COLORS {46}, HSIZE {sizeof(h8)};
    H3R_NS::OS::Memmove (h8 + W, &w, 4); // *(int *)(h8 + W) = w;
    H3R_NS::OS::Memmove (h8 + H, &h, 4); // *(int *)(h8 + H) = h;
    H3R_NS::OS::Memmove (h8 + BPP, &bpp, 2);
    int bmp_size = (w * bytes_per_pixel + bbpl) * h;
    H3R_NS::OS::Memmove (h8 + BMPSIZE, &bmp_size, 4);
    // *(int *)(h8 + BMPSIZE) = w * h * (bpp >> 8);
    H3R_NS::Array<H3R_NS::byte> pal;
    if (8 == bpp) {
        for (int i = 0; i < 256; i++) {
            // H3R_NS::byte rgba[] = {p[3*i], p[3*i+1], p[3*i+2], 0};
            // the source should be RGB; e.g. the BMP requires BGR
            H3R_NS::byte rgba[] = {p[3*i+2], p[3*i+1], p[3*i], 0};
            pal.Append (rgba, 4);
        }
        *(h8 + COLORS + 1) = *(h8 + COLORS + 5) = 1;
    }
    else if (24 == bpp)
        // for (int i = 0; i < (bmp_size - 3); i+=3) // RGB -> BGR or BGR -> RGB
        //    { auto t = *(b+i); *(b+i) = *(b+i+2), *(b+i+2) = t; }
        ;
    else H3R_ENSURE(false, "unknown bpp")
    int bmpofs = HSIZE + pal.Length (), fsize = bmpofs + bmp_size;
    H3R_NS::OS::Memmove (h8 + FSIZE, &fsize, 4);
    H3R_NS::OS::Memmove (h8 + BMPOFS, &bmpofs, 4);
    // *(int *)(h8 + FSIZE) = 54 + pal.Length () + bmp_size;
    // *(int *)(h8 + BMP) = 54 + pal.Length ();

    H3R_NS::OS::Log_stdout ("old fname: %s" EOL, fn);
    auto len = H3R_NS::OS::Strlen (fn);
    if (len > 4) fn[len-3] = isupper (fn[len-3]) ? 'B' : 'b',
                 fn[len-2] = isupper (fn[len-2]) ? 'M' : 'm',
                 fn[len-1] = isupper (fn[len-1]) ? 'P' : 'p',
                 fn[len-4] = '.';
    else H3R_ENSURE (false, "unsuported filename")
    H3R_NS::OS::Log_stdout ("new fname: %s" EOL, fn);
    H3R_NS::OS::FileStream s {fn,
        H3R_NS::OS::FileStream::Mode::WriteOnly};
    s.Write (h8, HSIZE);
    if (pal.Length () > 0) s.Write (pal.Data (), pal.Length ());
    // no :) s.Write (b, bmp_size); nothing is simple with these people
    H3R_NS::Array<H3R_NS::byte> zeroes {bbpl};
    for (int i = h-1; i >= 0; i--) {
        s.Write (b + i * w * bytes_per_pixel, w * bytes_per_pixel);
        if (bbpl > 0) s.Write (zeroes.Data (), zeroes.Length ());
    }
}