Sun Microsystems, Inc.

Alan E Bell

James P Lerner

In a computer system, an arrangement for storing condition signals indicative of the position of a pointing device and the condition of a button thereof, apparatus for comparing present condition signals generated by a pointing device with stored signals indicative of a previous condition of the pointing device, and apparatus responsive to the comparison of present condition signals generated by a pointing device for generating a pointer interrupt signal only if a change in the pointer condition has occurred.

System for storing a history of sampled pointer signals when a pointer

A method and apparatus which provides for the real time comparison of raster data. The raster data is stored in memory such that raster data corresponding to a specific X-Y coordinate location is consistently written to the same memory location. During the process of storing the data in memory, the data currently stored in the memory is read and compared to the data to be written into the same location in memory. If the data is not the same, the discrepancy and location of the discrepancy is noted in a separate area of memory to be used for subsequent analysis and the data to be written to that location is immediately written into the memory. The method and apparatus of the present invention is particularly applicable to the video graphics environment wherein the current bit of raster image contained in the frame buffer is compared to the updated raster image and the data changes are noted on a pixel by pixel basis. Utilizing the information gathered on the changed pixels, the video display need only update the changed data, thereby minimizing the amount of data to be transferred and increasing the speed of the system. In a preferred embodiment, the method and apparatus of the present invention is employed to provide an interface between a video adapter such as a video graphics array (VGA) and video display system incompatible with the video adapter such as a windowing system whereby the video output generated by the video adapter is translated and input to the video display system for generation of the display in real time.

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Westford, MA, United States of America

Alan E Bell