1. Field of the Invention
This invention relates to logic circuitry and, more particularly, to logic circuitry for a computer system which may be utilized to dynamically select among a number of particular individual display formats from a constant sized display memory.
2. History of the Prior Art
One common interface used for computer operations utilizes multiple "windows" displayed on a cathode-ray tube to represent individual computer applications. In a system using windows, more than one program at a time is placed in portions of memory which are available for instant call. The text and graphics output of each such program is made to appear on the cathode ray tube screen in a particular set of defined boundaries called a window. Each window may overlap other windows.
Window systems have several advantages. A user may switch between different activities which involve interaction with a display device without completely changing the appearance of the display. In addition, in multiprocessing of and multitasking systems, several processes can use the display to communicate information to the user.
One system utilizing windows is disclosed in U.S. patent application Ser. No. 07/254,957, Apparatus for Rapidly Clearing the Output Display of a Computer System, Joy et al., filed Oct. 7, 1988, and assigned to the assignee of the present invention. The system disclosed therein is especially useful for providing animated output because of its ability to rapidly switch between images presented on the output display without the necessity of clearing its display memories and other associated memories. In order to accomplish this, the system utilizes double-buffered full-screen-bitmapped display memories which may be rapidly switched to the output display.
In order to provide for windowing, this system utilizes a full-screen-bitmapped window identification memory and associated logic circuitry for determining whether the information in a particular display memory falls within the window to be displayed on the output display. The system is especially useful because it provides automatic clipping of overlapping windows.
Although such a system is very useful, a number of additional facilities would make it even more useful. For example, the preferred embodiment of the computer system above disclosed provides double-buffered display memories capable of storing twenty-four bits of RGB color information for display at each pixel of a cathode ray tube. Although double-buffered display memories are useful for the rapid switching between frames required by animated applications; such display memories are unnecessary for applications which are not used to display animated graphics. Consequently, such a system would be enhanced were it capable of selectively utilizing single- or double-buffered display memories.
Moreover, although some applications are capable of utilizing twenty-four bits of RGB color memory at each pixel position, the number of colors and hues utilized by many programs is much less. Consequently, a system which provides the ability to select the number of bits utilized for storing information to be displayed at individual pixels of the output display would make more efficient use of the hardware of the computer system and thus prove useful in a computer system.
Additionally, either of the foregoing improvements in a computer system frees memory which might advantageously be made available to enhance other operations of the computer system.
It is, therefore, an object of the present invention to provide a computer system which includes logic circuitry for use in determining whether the system will utilize single- or double-buffered display memories for a particular window.
It is another object of this invention to provide a computer system which provides for multiple uses of the display memory.
It is another object of this invention to selectively control the translation of data from display memories to the colors realized on the output display.
It is an additional object of the present invention to utilize pre-existing memory in a computer system to provide for the rapid selection of colors and hues to be utilized by different programs on an output display of that system.