wxCOMPOSITION_CLEAR, /* R = 0 */
wxCOMPOSITION_SOURCE, /* R = S */
wxCOMPOSITION_OVER, /* R = S + D*(1 - Sa) */
wxCOMPOSITION_CLEAR, /* R = 0 */
wxCOMPOSITION_SOURCE, /* R = S */
wxCOMPOSITION_OVER, /* R = S + D*(1 - Sa) */
wxCOMPOSITION_XOR, /* R = S*(1 - Da) + D*(1 - Sa) */
// mathematical compositions
wxCOMPOSITION_XOR, /* R = S*(1 - Da) + D*(1 - Sa) */
// mathematical compositions