Graphics data processing apparatus for graphic image operations upon

Abstract

The graphics data processing apparatus performs graphic data processing operations by combining data from two image arrays in accordance with a predetermined operation. This raster operation involves forming an image array having a pixel color code for each pixel of the combined image array formed from a combination of the color codes of corresponding pixels of the source and destination image arrays. The present invention includes a pair of data registers which define the difference in memory address between vertically adjacent pixels for the respective image arrays. This difference in memory address between vertically adjacent pixels is called the pitch and corresponds generally to the width of the display image in address space when any horizontal blanking interval is taken into account. In the present invention such raster operations can be performed on data which is stored in formats of differing pitch. This capability enables standard typefaces and icons to be stored in a default pitch while still being usable for a variety of display applications. In addition, even in the case in which both the source and destination pitches are the same, the capability for controlling the pitch for raster operations permits the same graphics data processing apparatus to operate in a variety of display applications. Thus the flexibility of operation and ease of application to differing graphics display problems is enhanced.