//-------------------------------------------------------------------------
    // tetris pieces
    //
    // blocks: each element represents a rotation of the piece (0, 90, 180, 270)
    //         each element is a 16 bit integer where the 16 bits represent
    //         a 4x4 set of blocks, e.g. j.blocks[0] = 0x44C0
    //
    //             0100 = 0x4 << 3 = 0x4000
    //             0100 = 0x4 << 2 = 0x0400
    //             1100 = 0xC << 1 = 0x00C0
    //             0000 = 0x0 << 0 = 0x0000
    //                               ------
    //                               0x44C0
    //
    //-------------------------------------------------------------------------