This routine follows the pattern set by eddh_SrcDestBlt and eddh_PatDestBlt. Destination invert raster operations are translated into source invert raster operations in EDDNBBLT.C. This translation might have to be changed on your hardware. Almost all hardware blt engines support inversion of the destination, but many won't invert the source, if the source and destination are identical. The raster operation should be "not destination." Instead, it is mapped to "not source" and the source and destination are created to be the same.