Method and system for transmitting data for a shared application

• US 6,911,987 B1
• Filed: 05/08/2000
• Issued: 06/28/2005
• Est. Priority Date: 07/05/1995
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Picturetel Corporation (HP Inc.), Microsoft Corporation
• Inventors: MacFarquhar, Roderick F., Pollitt, Alex J., Batty, John P., Downes, Anthony M., Hughes, Kenneth P., Mairs, Christopher J., Berry, Mark E.
• Primary Examiner(s): Gaffin, Jeffrey
• Assistant Examiner(s): PEYTON, TAMMARA R
• Application Number:
  US09/566,309
• Time in Patent Office: 1,877 Days
• Field of Search: 710/6, 710/33, 709/204, 709/205, 345/502, 345/522, 345/733, 345/557, 345/501, 345/27, 345/555
• US Class Current: 345/557
• CPC Class Codes: G06F 3/1462 with means for detecting differences between the image stored in the host and the images displayed on the remote displays
• CPC Class Codes: G06T 9/005 Statistical coding, e.g. Huffman, run length coding

Abstract

A method and system for compressing bitmap data in a system for sharing an application running on a host computer with a remote computer, wherein the shared application'"'"'s screen output is simultaneously displayed on both computers. Simultaneous display of screen output is achieved by efficiently transmitting display data between the host computer and the remote computer. When a font used by the host computer for displaying text is not available on the remote computer, the host computer sends a bitmap representation of the text for display, rather than the text itself. Bitmap representations are cached by the remote computer, so that the same bitmap representation need not be repeatedly transmitted from the host computer to the remote computer. Bitmap representations are compressed by the host computer prior to transmission, transmitted, then decompressed by the remote computer.

Claims

1. A method for transmitting representations of bitmaps from a first computer system to a second computer system, the method comprising:

under control of the first computer system, under control of the first computer system;

receiving a request to send a bitmap to the second computer system;

determining whether the bitmap has been previously sent to the second computer system;

when it is determined that the bitmap has not been previously sent to the second computer program, sending the bitmap to the second computer system; and

when it is determined that the bitmap has been previously sent to the second system,

determining whether the bitmap has been cached by the second computer system;

when it is determined that the bitmap has not been cached by the second computer system, sending the bitmap to the second computer system along with an indication to cache the bitmap; and

when it is determined that the bitmap has been cached by the second computer system, sending an indication of the cached bitmap to the second computer system.

2. The method of claim 1 including before sending the bitmap, compressing the bitmap, the bitmap having data organized into rows, each row having a number of bits, each bit having a 0-bit value or a 1-bit value, by:

outputting a run-length encoding of the first row of data;

for each row of the bitmap except for the first row,

generating an interim row having the number of bits by setting the bit value of each bit in the interim row to the exclusive-OR of a corresponding bit in the row and of a corresponding bit in a previous row; and

outputting a run-length encoding of the interim row of data.

3. A method for transmitting representations of bitmaps from a first computer system to at least a second computer system, the method comprising:

receiving a request to send a bitmap to the second computer system;

determining whether the bitmap has been previously sent to the second computer system;

when it is determined that the bitmap has not been previously sent to the second computer,

sending the bitmap to the second computer system; and

when it is determined that the bitmap has been previously sent to the second computer system,

determining whether the bitmap has been cached by the second computer system;

when it is determined that the bitmap has not been cached by the second computer system, sending the bitmap to the second computer system along with an indication to cache the bitmap; and

when it is determined that the bitmap has been cached by the second computer system,

sending an indication of the cached bitmap to the second computer system.

4. The method of claim 3 including before sending the bitmap, compressing the bitmap, the bitmap having data organized into rows, each row having a number of bits, each bit having a 0-bit value or a 1-bit value, by:

outputting a run-length encoding of the first row of data;

for each row of the bitmap except for the first row,

generating an interim row having the number of bits by setting the bit value of each bit in the interim row to the exclusive-OR of a corresponding bit in the row and of a corresponding bit in a previous row; and

outputting a run-length encoding of the interim row of data.

5. A method of processing bitmaps sent from a first computer system to a second computer system, the method comprising:

when receiving a bitmap sent from the first computer system, displaying the received bitmap;

when receiving a bitmap sent from a computer system along with an indication to cache the bitmap, displaying and caching the received bitmap; and

when receiving an indication of the cached bitmap, retrieving and displaying the cached bitmap.

6. A system for transmitting representations of bitmaps from a first computer system to a second computer system, the system comprising:

a first component that receives a request to send a bitmap to at least the second computer system, that when the bitmap has not been previously sent to the second computer program, sends the bitmap to the second computer system, and that, when the bitmap has been previously sent to the second computer system and when the bitmap has not been cached by the second computer system, sends the bitmap to the second computer system along with an indication to cache the bitmap and when the bitmap has been cached by the second computer system, sends an indication of the cached bitmap to the second computer system.

7. The system of claim 6 wherein the first component before sending the bitmap compresses the bitmap, the bitmap having data organized into rows, each row having a number of bits, each bit having a 0-bit value or a 1-bit value, by:

outputting a run-length encoding of the first row of data;

for each row of the bitmap except for the first row,

generating an interim row having the number of bits by setting the bit value of each bit in the interim row to the exclusive-OR of a corresponding bit in the row and of a corresponding bit in a previous row; and

outputting a run-length encoding of the interim row of data.

8. The system of claim 6, wherein the first component indications are capable of being responded to by a second component in one or more computer systems.