Line mover for bit-mapped display

The pixel contents of a frame buffer scan line segment are moved from a source location to a destination location by reading fields of the source segment into a source data shift register and fields of the destination segment into a destination data shift register. The contents of the shift registers may then be rotated relative to one another to account for different starting locations within source and destination fields. The contents of the two shift registers are then simultaneously and synchronously shifted into an ALU where a replacement rule may be used to create a modified stream of pixels shifted into the emptying portion of the destination data shift register. At the conclusion of the shifting for that field the destination data shift register contains the proper pixels to be written back to the destination location in the frame buffer. Then the process is repeated for any remaining fields in the segment being moved. In the special case of scrolling a vertical column the fields are read directly into the destination data shift register and immediately rewritten to the destination location.