Method and apparatus for detecting changes in raster data

In a computer graphics system for the generation and display of raster data images comprising a central processing unit (CPU) coupled to a memory means said CPU further being coupled to a display means for the display of a raster data image, said raster data image comprising a plurality of pixels, each identified at an X-Y coordinate location within the raster data image, an apparatus for companying a first and a second raster data image in real time wherein a pixel at a specific X-Y coordinate location in the second raster data image is compared to a pixel at the specific X-Y coordinate location in the first raster data image as each pixel of the second raster data image is generated, said apparatus comprising:

• means for writing the first raster data image into memory such that each data representative of a pixel at a predetermined X-Y coordinate location in the image is written to predetermined memory location;
• means for receiving a pixel data of the second image being generated, said pixel data representative of a pixel located at the specific X-Y coordinate location in the second raster data image;
• means for reading the first raster data image stored in memory to retrieve pixel data corresponding to a pixel in the first raster data image at the specific X-Y coordinate location;
• a comparator circuit which receives as input and compares the pixel data read from memory and the pixel data of the second raster data image received;
• and
• means for recording the identification of the X-Y coordinate location of the pixel data to indicate that the pixel data has changed if the comparator output indicates that the pixel data read of memory and the corresponding pixel data from the second raster data image are not the same.

A method for interfacing output generated by a video graphics adapter to a graphics display system incompatible with the video graphics adapter, said video graphics adapter generating a raster data image in a first format and said graphics display system receiving as input a raster data image in a second format, said raster data image comrpising plurality of pixels, each pixel identified at an X-Y coordinate location within the raster data image said method for interfacing comprising:

• writing a raster data image in said first format generated by the video graphics adapter into memory such that each pixel data representative of a pixel at a predetermined X-Y coordinate location in the image is written to a predetermined memory location;
• receiving pixel data of a second raster data image a pixel at a time from said video graphics adapter, said pixel data being in said first format generated by the video graphics adapter and representative of a pixel at a specific X-Y coordinate location in the second raster data image, said second raster data image generated subsequent to said first raster data image;
• reading pixel data from a predetermined memory location representative of a pixel of the first raster data image at the specific X-Y coordinate location:
• inputting to a comparator circuit the pixel data of the first raster data image read from memory and pixel data of the second raster data image received from the video graphics adapter;
• if the pixel data of the first raster data image read from the memory and the pixel data of the second raster data image received from the video graphics adapter are not the same, storing the identification of the X-Y coordinate location of the pixel to indicate that the pixel has changed from the pixel data of the first raster data image to the pixel data of the second raster data image:
• writing the pixel data from the second raster data image into memory at the predetermined memory location which corresponds to the X-Y coordinate location of the corresponding pixel in the first raster data image;
• translating the pixel data, from the second data raster image which has changed, from the first raster data format to the second raster data format;
• inputting the tranalated pixel data to the graphics display system in the second raster data format compatible with the graphics display system for output to the display means;
• and
• updating portions of the display corresponding to the locations of the pixels which have changed with the translated pixel data thereby updating the display from the first raster data image to the second raster data image.

In a computer graphics system comprising a display means for the display of raster data image, said raster data image being in a second raster data image format, said display means displaying a first raster data image said raster data image comprising a plurality of pixels, each pixel identified at an X-Y coordinate location within the image, an apparatus for updating the display means with a second raster data image in real time as the second raster data image is generated by a video graphics adapter, said second raster data image being generated by a video graphics adapter, said second raster data image being generated in a first raster data image format incompatible with the second raster data image format, said apparatus comprising:

• a first memory means for storing the first raster data image in the first format;
• means for writing the first raster data image into the first memory means such that each pixel data representative of a pixel at a predetermined X-Y coordinate location in the image is written to a predetermined memory location;
• means for receiving the second raster data image as each pixel is generated by the video graphics adapter, said second raster data image generated subsequent to said first raster data image, each pixel data received being representative of a pixel at a specific X-Y coordinage location in the second raster data image;
• means for reading pixel data of the first raster image from the first memory means at a predetermined memory location corresponding to the specific X-Y coordinate location;
• a comparator circuit which compares the pixel data read from the memory and pixel data generated for the second raster data image to determine whether the pixel has changed from the first raster data image to the second raster data image;
• a second memory means for storing the identification of the pixel location to indicate that the pixel has changed from the first raster data image to the second raster image, if the pixel data read from the first memory means and the corresponding pixel data generated for the second raster data image are not the same;
• means for translating the pixel data, generated for the second raster data image of the pixels which have changed, from the first raster data format to the second raster data format;
• and
• means for inputting the translated pixel data to the computer graphics system in the second raster data format compatible with the computer graphics system for output to the display means;
• whereby the computer graphics system updates portions of the display means corresponding to the changed pixels with the translated pixel data from the second raster data image.