Apparatus and method for reading and writing text characters in a graphics display

Abstract

Apparatus and method for writing text characters to a raster scan video display operted in an all-points-addressable, or graphics, mode, and for reading characters thus written. A graphic video display buffer directly refreshes the display with graphics data received from a microprogrammed processor. The processor writes a character to the display by selecting and loading into the graphics video display buffer a text character dot pattern retrieved from main storage, and reads a character previously written by comparing a dot pattern retrieved from the display buffer with dot patterns retrieved from main storage. To write a character to the display in color, the graphic dot image of a selected character retrieved from main storage is expanded to a selected pixel and color format, and stored in the graphics video display buffer. Text characters thus written in color are read by retrieving from the display buffer the expanded dot image, restoring the expanded dot image to its original form, and comparing the restored dot image with graphic dot images retrieved from storage. This is a Reissue of a Patent which was the subject of a Reexamination Certificate No. B1 Re. 32,201, dated Aug. 1, 1989, Request No. 90/001,645, Nov. 23, 1988.

I claim: .Badd..[. 
     
       1.  A raster scan video display control apparatus of the type including a graphic video display refresh buffer operable in an all points addressable mode for refreshing said display with graphics data, a processor for writing graphic data into said display refresh buffer, and a character storage for storing the character dot patterns of a display character font, characterized by: means for selecting a character to be displayed; and   programmable control means referenced by said processor for (1) loading from said storage into said graphic video display refresh buffer a character dot pattern corresponding to the character to be displayed;   (2) expanding the selected character dot pattern into a predetermined pixel format and then color encoding the expanded dot pattern to establish a resultant expanded/encoded dot pattern; and   (3) loading said expanded/encoded dot pattern into said graphic video display refresh buffer..]..Baddend. .Badd..[.2. A raster scan video display control apparatus of the type including a graphic video display refresh buffer operable in an all points addressable mode for refreshing said display with graphics data, a processor for writing graphic data into said display refresh buffer, and a character storage for storing the character dot patterns of a display character font, characterized by:     means for selecting a character to be displayed; and   programmable control means referenced by said processor selectively for loading from said storage into said graphic video display refresh buffer a character dot pattern corresponding to the character to be displayed and for reading a previously displayed character by comparing a character dot pattern previously loaded into said graphic video display buffer with successive character dot patterns selected from said character   
     
     
        storage..]..Baddend. 3.  A method for writing a text character on a raster scan all points addressable video display, comprising the steps of: retrieving from storage the graphic dot image of the .Iadd.text .Iaddend.character to be written.Iadd., each dot being represented by a single bit.Iaddend.;   expanding said graphic .Iadd.dot .Iaddend.image to a selected pixel and color format .Iadd.by duplicating each bit and logically combining the bits representing each dot with encoded color information.Iaddend.; and   storing the expanded dot image .Iadd.by placing the bits representing each dot .Iaddend.in .Iadd.contiguous address memory locations in .Iaddend.a   
     
     
        display refresh buffer. 4.  A method for reading a selected text character previously written as an expanded dot image into a display refresh buffer from a graphic dot image stored in a storage associated with an all points addressable video display, comprising the steps of: retrieving from said display refresh buffer the expanded dot image of the selected character to be read;   converting the expanded dot image to be read to a converted dot image corresponding to the format of graphic dot image in the storage;   obtaining from storage the graphic dot image of a comparison character;   comparing the dot image of the comparison character with said converted dot image; and   repeating the obtaining and comparing steps until the dot image of the   
     
     
        comparison character matches said converted dot image. 5.  A method for operating a computing apparatus that controls a graphics display to write a text character onto a display screen, the computing apparatus including a processor referencing a store, and a display refresh buffer .Iadd.comprising a plurality of memory locations.Iaddend., characterized in that the method comprises the steps of: establishing addressability to the location in said display refresh buffer to receive a selected display text character;   establishing addressability to the location in said store containing a dot image of said selected display text character;   fetching one portion of said dot image from said store.Iadd., each dot being represented by a single bit.Iaddend.;   expanding said portion of said dot image according to a selected pixel format .Iadd.by duplicating each bit .Iaddend.to provide an expanded dot image portion;   modifying said expanded dot image portion .[.to encode a desired color.]. .Iadd.by logically combining the bits representing each dot with encoded color information to provide an encoded color dot image portion.Iaddend.; and   storing the .[.expanded.]. .Iadd.bits representing each dot in the encoded color .Iaddend.dot image portion .[.as modified.]. in .Iadd.contiguous address memory locations in .Iaddend.said display refresh buffer; and   repeating said fetching, expanding, modifying and storing steps for each portion of said dot image to load into said display refresh buffer the   
     
     
        selected display text character. 6.  The method of claim .Badd..[.7,.]..Baddend. .Iadd.5, .Iaddend.characterized by the steps of: refreshing a raster scan display with alternate raster scan lines refreshed from offset locations of said display refresh buffer; and   storing alternating dot image portions in offset locations of said display   
     
     
        refresh buffer as part of said storing step. 7.  The method of claim .Badd..[.7,.]..Baddend. .Iadd.5, .Iaddend.characterized in that said storing step is performed by exclusive 'ORing each dot image portion with a corresponding portion of a modified expanded dot image previously stored 
     
     
        in said display refresh buffer. 8.  The method of claim 5, characterized in that said expanding step and said modifying step are for the purpose of writing a text character in color and said expanding step and modifying step are eliminated when writing the text character in black and white. 
     
     
            A method for operating a computing apparatus that controls a graphics display to read a text character previously written onto said graphics display, the computing apparatus including a processor referencing a store, and a display refresh buffer, comprising the steps of: retrieving from said display refresh buffer a dot image of the character to be read;   storing the dot image of the character to be read in a save area in said store;   sequentially retrieving from said store respective dot images of possible display text characters and comparing each respective dot image with the dot image in the save area; and   repeating the retrieving and comparing steps until a respective dot image matches the dot image in said save area, thereby concluding reading of the text characters. .Iadd.10. A raster scan video display control apparatus of the type including a graphic video display refresh buffer operable in an all points addressable mode for refreshing said display with graphics data, a processor for writing graphics data into said display refresh buffer, and a character storage for storing the character dot patterns of a display character font, comprising means for selecting a character to be displayed, and means for loading from said storage into said graphic video display refresh buffer a character dot pattern corresponding to the character to be displayed and for reading a previously displayed character by comparing a character dot pattern previously loaded into said graphic video display buffer with successive character dot patterns selected from said character storage. .Iaddend. .Iadd.11. A raster scan video display control apparatus of the type including a graphic video display refresh buffer comprising a plurality of memory locations for refreshing said display with graphics data, a processor for writing graphics data into said display refresh buffer, and a character storage for storing the character dot patterns of a display character font, comprising means for selecting a character to be displayed, means for reading out said character from said character storage in a first dot format comprising one bit per dot, means for expanding by duplicating the selected character dot pattern into a predetermined pixel format comprising two identical bits per pixel and then color encoding the expanded dot pattern by logically combining encoded color information with said expanded dot pattern to establish a resultant expanded/encoded dot pattern, and loading the bits representing each dot of said expanded/encoded dot pattern into contiguous address memory locations in said graphic video display refresh buffer. .Iaddend. .Iadd.12. In a display apparatus for writing a text character onto a video display and including a means for retrieving the graphic dot image of the character to be written from a character storage, each dot in said image being represented by a single bit, the improvement comprising means for expanding a retrieved graphic dot image into a selected pixel and color format by duplicating each bit n times and logically combining the n bits representing each dot with n bits of encoded color information, where n is an integer, and   means for storing the expanded dot image in a display refresh buffer by entering the n bits representing each dot of said expanded dot image into n contiguous address memory locations. .Iaddend. .Iadd.13. Video display control apparatus of the type including a video display buffer having a plurality of memory locations for holding information patterns directly specifying the tracing of multi-element patterns on a display screen, a processor for writing information patterns into said buffer, and font storage means for storing a font of displayable information patterns, characterized by:   means for selecting code representations of patterns to be displayed;   means responsive to said selected representations for extracting first multi-element information patterns corresponding to said .[..[.multi-element.]..]. .Badd.displayable information .Baddend.patterns.Badd., said multi-element information patterns being .Baddend.extracted from said font storage means, each element of said first patterns being represented by a first number of bits n, where n is an integer;   means for converting said extracted first patterns into corresponding second multi-element information patterns, each element of said second patterns being represented by a second number of bits 2n, for producing the same display patterns as said first patterns but with a different image characteristic; and   means for entering said second multi-element information patterns into said display buffer by storing the 2n bits representing each element of said second patterns in 2n contiguous address memory locations.  .Iadd.14. Video display control apparatus of the type including a video display buffer for holding information patterns directly specifying the tracing of image patterns on a display screen, a processor for writing information patterns, into said buffer, and font storage means for storing a font of displayable information patterns, characterized by:   means for selecting code representations of image patterns to be displayed;   means responsive to said selected representations for extracting corresponding information patterns from said font storing means;   means responsive to said extracting means for storing information patterns corresponding to said extracted patterns in said display buffer,   means for reading information patterns from said display buffer; and   means coupled to said reading means and said font storage means for converting information patterns read from said buffer into corresponding   
     
     
        code representations. .Iaddend. .Iadd.15.  A video display control apparatus in accordance with claim 14 wherein said converting means comprises: means for comparing each information pattern read from said display buffer with patterns stored in said font storage means; and   means responsive to a match between patterns compared by said comparing means for developing a code representation corresponding to the matched pattern. .Iaddend. .Iadd.16. Video display control apparatus in accordance with claim 14 wherein said means for storing corresponding patterns in said display buffer comprises:   means for converting each pattern extracted from said font storage into a corresponding pattern having a different display image characteristic than the extracted pattern; and   means for writing such corresponding patterns into said display buffer. .Iaddend. .Iadd.17. A method for creating image displays of multi-element information patterns comprising:   forming code representations of said multi-element information patterns to be displayed.[..[., each element being represented by a first number of bits.]..].;   converting said code representations into corresponding first multi-element information patterns corresponding to images to be displayed, each element .Badd.of said first patterns .Baddend.being represented by a .[..[.second number of bits greater than said.]..]. first number of bits;   converting said first multi-element information patterns into second multi-element information patterns for directly controlling the tracing of associated image patterns on an image display by .Badd.expanding said first number of bits into a second number of bits, greater than said first number of bits, and .Baddend.logically combining attribute information encoded in a .Badd.number of bits, equal to said .Baddend.second number of bits, with the bit representation for each element of said second multi-element information patterns; said second information patterns having associated image characteristics different from those of the respective first information patterns; and   storing .Badd.the bits of .Baddend.said second information patterns in contiguous address memory locations of a display buffer capable of directly controlling the formation of images on an image display. .Iadd.18. A method for creating image displays of information patterns comprising:   forming code representations of information patterns to be displayed;   converting said code representations into corresponding information patterns to be displayed;   storing said information patterns in a display buffer capable of directly controlling the formation of images on an image display;   reading information patterns from said display buffer, and   converting said information patterns read from said display buffer into corresponding code representations. .Iaddend. .Iadd.19. The display formation method of claim 18 wherein: said step of converting said code representations into corresponding information patterns comprises:   converting each code representation into a first associated information pattern having a first associated image formation characteristic; and   converting each first associated information pattern into a different second information pattern having an associated second image formation characteristic different from the respective first characteristic. .Iaddend. .Iadd.20. The display formation method of claim 19 wherein said step of converting said information patterns into code representations comprises:   converting each information pattern into a corresponding standardized information pattern having a different image formation characteristic; and   converting each said corresponding pattern into a corresponding standardized code representation. .Iaddend.