You reboot the machine. A color BeOS desktop greets you. The blit width register is set to the number of bytes copied per row. Your code reflects this statement. You reboot the machine.
Windows now drag normally, except for some weirdness at the left edge of the screen.
It looks as if the left four columns of pixels are being blitted 64 pixels too high. There is nothing in the docs to explain this behavior. You are in a Web site. There are many links here. There is no developer support here.