If GGO_BITMAP, GGO_GRAY2_BITMAP, GGO_GRAY4_BITMAP, GGO_GRAY8_BITMAP, or GGO_NATIVE is specified and the function succeeds, the return value is greater than zero; otherwise, the return value is GDI_ERROR. If one of these flags is specified and the buffer size or address is zero, the return value specifies the required buffer size, in bytes. If GGO_METRICS is specified and the function fails, the return value is GDI_ERROR.
看看这个别人用的!