16. Tiny Tile

A tiny tile is a 8x8 tile that can be specified in only 3 bytes. It does this breaking up the tile into 4-bit 2x2 blocks, and then restricting those blocks to be only 2 patterns. The first byte stores what those two patterns are, and then the 2 remaining bytes store the indexes.

void btprnt_draw_tinytile(btprnt_region *r,
                          int xpos,
                          int ypos,
                          int b0,
                          int b1,
                          int b2);

void btprnt_draw_tinytile(btprnt_region *r,
                          int xpos,
                          int ypos,
                          int b0,
                          int b1,
                          int b2)
{
    int x, y;
    b0 &= 0xff;
    b1 &= 0xff;
    b2 &= 0xff;

    for (y = 0; y < 4; y++) {
        for (x = 0; x < 4; x++) {
            unsigned char pat;
            int xoff, yoff;

            if (y < 2) {
                pat = (b1 >> (4 * y)) & (1 << x);
            } else {
                pat = (b2 >> (4 * (y - 2))) & (1 << x);
            }

            pat = (pat ? (b0>>4) : b0) & 0xf;

            xoff = (x<<1) + xpos;
            yoff = (y<<1) + ypos;

            btprnt_region_draw(r,
                               xoff, yoff,
                               pat & 1);
            btprnt_region_draw(r,
                               xoff + 1, yoff,
                               (pat & 2) >> 1);
            btprnt_region_draw(r,
                               xoff, yoff + 1,
                               (pat & 4) >> 2);
            btprnt_region_draw(r,
                               xoff + 1, yoff + 1,
                               (pat & 8) >> 3);
        }
    }
}

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