Method and logic system for the rotation of raster-scan display images

An image rotation device, comprising:

• a frame buffer having a plurality of locations for storing pixel data, wherein each of said locations represents N pixels;
• and
• a hardware rotation unit coupled to said frame buffer and configured to receive an input address and pixel data corresponding to a first image, wherein said hardware rotation unit stores said pixel data in said frame buffer as a second image, wherein said pixel data is stored in locations in said frame buffer according an output address generated by said hardware rotation unit for each input address, wherein said output address is generated according to a sum of a third term and a fifth term minus a sixth term, wherein:
• a first term equal to the quotient of a division of a number of pixels per horizontal line (H) of said first image by the number of pixels (N) associated with each location in said frame buffer;
• a second term equal to said input address (ADDR.sub.-- IN) modulo said first term, wherein said modulo operation produces the remainder of an integer division of said input address (ADDR.sub.-- IN) by said first term;
• said third term equal to the product of said second term and a number of horizontal lines (W) of said first image;
• a fourth term equal to the quotient of a division of the number of horizontal lines of said first image (W) by the number of pixels (N) associated with each location in said frame buffer;
• said fifth term equal to said fourth term minus the quantity 1;
• and
• said sixth term equal to the quotient of an integer division of said input address (ADDR.sub.-- IN) by the number of pixels per horizontal line (H) of said first image.

A computer system comprising:

• a video controller coupled between a system bus and a display device, said video controller adapted to:
• receive an input address and corresponding pixel data associated with a first image from said system bus;
• and
• transmit display information to said display device;
• and
• said video controller comprises:
• a frame buffer having a plurality of locations for storing pixel data, wherein each of said locations represents N pixels;
• an address calculator unit coupled to said frame buffer and configured to receive an input address for a first image, said input address corresponding to one of said locations in said frame buffer, and wherein for each said input address said address calculator unit is further configured to provide N output addresses for a second image, each output address corresponding to one of said locations in said frame buffer;
• a data assembly unit coupled to said frame buffer and configured to receive pixel data associated with said input address and configured to modify a portion of the pixel data for one pixel stored in each location in said frame buffer corresponding to said N output addresses and leaving the remaining pixel data unmodified in each location in said frame buffer corresponding to said N output addresses;
• and
• an image display system coupled between said frame buffer and said display device, said display system adapted to receive data from said frame buffer, convert said data received from said frame buffer into said display information, and transmit said display information to said display device.

A computer system comprising:

• a video controller coupled between a system bus and a display device, said video controller adapted to:
• receive an input address and corresponding pixel data associated with a first image from said system bus;
• and
• transmit display information to said display device;
• and
• said video controller comprises:
• a frame buffer having a plurality of locations for storing pixel data, wherein each of said locations represents N pixels;
• a hardware rotation unit coupled to said frame buffer and configured to receive an input address and pixel data corresponding to a first image, wherein said hardware rotation unit stores said pixel data in said frame buffer as a second image, wherein said pixel data is stored in locations in said frame buffer according an output address generated by said hardware rotation unit for each input address, wherein said output address is generated according to a sum of a third term and a fifth term minus a sixth term, wherein:
• a first term equal to the quotient of a division of a number of pixels per horizontal line (H) of said first image by the number of pixels (N) associated with each location in said frame buffer;
• a second term equal to said input address (ADDR.sub.-- IN) modulo said first term, wherein said modulo operation produces the remainder of an integer division of said input address (ADDR.sub.-- IN) by said first term;
• said third term equal to the product of said second term and a number of horizontal lines (W) of said first image;
• a fourth term equal to the quotient of a division of the number of horizontal lines of said first image (W) by the number of pixels (N) associated with each location in said frame buffer;
• said fifth term equal to said fourth term minus the quantity 1;
• and
• said sixth term equal to the quotient of an integer division of said input address (ADDR.sub.-- IN) by the number of pixels per horizontal line (H) of said first image;
• and
• an image display system coupled between said frame buffer and said display device, said display system adapted to receive data from said frame buffer, convert said data received from said frame buffer into said display information, and transmit said display information to said display device.

A method for modifying pixel information associated with a raster-scan portrait image to display a raster-scan landscape image, comprising:

• receiving an input address corresponding to a pixel data location for said portrait image;
• receiving pixel data associated with said input address, wherein said pixel data represents N pixels;
• calculating a base address derived from said input address, an offset address, and a byte position;
• modifying a location in a frame buffer with said pixel data, wherein said location corresponds to said base address added to a multiple of said offset address, wherein only the portion of said location indicated by said byte position is modified;
• and
• repeating said modifying N-1 times using an increasing multiple of said offset address for each repetition, wherein data for a different one of said N pixels represented by said pixel data is used to modify said location for each repetition.