Method for lossless bandwidth compression of a series of glyphs

• US 6,081,623 A
• Filed: 10/11/1995
• Issued: 06/27/2000
• Est. Priority Date: 10/11/1995
• Status: Expired due to Term

• Current Assignee: Citrix Systems, Inc. (Cloud Software Group)
• Original Assignee: Citrix Systems, Inc. (Cloud Software Group)
• Inventors: Krantz, Jeffrey Isaac, Bloomfield, Marc Alan
• Primary Examiner(s): Au, Amelia
• Assistant Examiner(s): Johnson, Timothy M.
• Application Number:
  US08/540,794
• Time in Patent Office: 1,721 Days
• Field of Search: 382/243, 382/232, 382/239, 382/305, 358/470, 358/403, 358/404, 358/430, 341/51, 341/55, 341/106, 341/107, 341/67, 345/203, 345/509, 345/192, 345/195
• US Class Current: 382/239
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00

Abstract

A lossless bandwidth compression method for use in a distributed processor system for communicating graphical text data from a remote application server to a user workstation over a low bandwidth transport mechanism enables the workstation display to support the illusion that the application program is running locally rather than at the remote application server. At the application server, the graphical text data is represented by a string of glyphs, each glyph being a bit mask representing the foreground/background state of the graphical text data pixels. Each unique glyph is encoded by assigning a unique identification code (IDC). Each IDC is compared with the previous IDCs in the string and, if a match is found, the IDC is transmitted to the workstation. If a match with a prior IDC is not found, the IDC and the corresponding glyph pattern are transmitted to the workstation. At the workstation, the IDCs are queued in the order received while the glyph patterns are cached using the corresponding IDCs as addresses. The string of glyphs is reconstructed by using the queued IDCs in their natural order for accessing the cached glyph patterns as required to reproduce the original string of glyphs.

Claims

1. A method for lossless bandwidth compression encoding of data for transmission of encoded data from an application server to a client workstation for decoding in a distributed process system, the data represented as a glyph pattern string comprising of plurality of glyphs, the method comprising:

(a) assigning a unique handle to a glyph in the glyph pattern string for identification;

(b) assigning a unique subcache handle to the glyph in the glyph pattern string; and

(c) generating a compressed glyph string for transmission to the client workstation by placing into the compressed glyph string;

(i) a first glyph identifier comprising the glyph, a chunk parameter, tile assigned handle, and the assigned subcache handle upon a first occurrence of the glyph in the glyph pattern string, the chunk parameter indicating the number of bytes required to store the glyph;

(ii) a second glyph identifier comprising the handle assigned to the glyph, a chunk parameter, and the subcache handle assigned to the glyph when the glyph has previously occurred in the glyph pattern string and the assigned handle is not one of a predetermined number of handles stored in a cache memory, the chunk parameter indicating the number of bytes required to store the glyph; and

(iii) a third glyph identifier comprising the subcache handle assigned to the glyph, and a chunk parameter, when the glyph has previously occurred in the glyph pattern string and the assigned handle is one of a predetermined number of handles stored in a cache memory, the chunk parameter indicating the number of bytes required to store the glyph.

2. The method of claim 1 further comprising the step of:

(d) repeating steps (a) through (c) for each glyph in the glyph pattern string.

3. The method of claim 1 wherein step (b) comprises assigning a unique subcache handle to each unique glyph in the glyph pattern string, each subcache handle comprising less bits than the handle assigned to the glyph.

4. The method of claim 1 wherein step (a) comprises assigning a unique handle of thirty-two bits to each unique glyph in the glyph pattern string for identification.

5. The method of claim 1 wherein step (b) comprises assigning a unique subcache handle of seven bits to each unique glyph in the glyph pattern string.

6. A method for lossless bandwidth compression encoding of data for transmission of encoded data from an application server to a client workstation for decoding in a distributed process system, the data represented as a glyph pattern string comprising of plurality of glyphs, the method comprising:

(a) at the application server

(i) assigning a unique handle to a glyph in the glyph pattern string for identification;

(ii) assigning a unique subcache handle to the glyph in the glyph pattern string; and

(iii) generating and transmitting to the client workstation a compressed glyph string by placing into the compressed glyph string;

(A) a first glyph identifier comprising the glyph, a chunk parameter, the assigned handle, and the assigned subcache handle upon a first occurrence of the glyph in the glyph pattern string, the chunk parameter indicating the number of bytes required to store the glyph;

(B) a second glyph identifier comprising the handle assigned to the glyph, a chunk parameter, and the subcache handle assigned to the glyph when the glyph has previously occurred in the glyph pattern string and the assigned handle is not one of a predetermined number of handles placed in the compressed glyph string, the chunk parameter indicating the number of bytes required to store the glyph; and

(C) a third glyph identifier comprising the subcache handle assigned to the glyph, and a chunk parameter, when the glyph has previously occurred in the glyph pattern string and the assigned handle is one of a predetermined number of handles placed in the compressed glyph string, the chunk parameter indicating the number of bytes required to store the glyph; and

(b) at the client workstation

(i) receiving the compressed glyph pattern string and storing each glyph in the compressed glyph pattern string at a memory element determined from the handle assigned to that glyph,

(ii) storing each assigned handle in the compressed glyph pattern string in a memory element determined by the subcache handle corresponding to that assigned handle, and

(iii) generating a decoded string of glyphs by sequentially using each subcache handle to retrieve assigned handles, and using each assigned handle in the compressed glyph string for retrieving a corresponding stored glyph and substituting a retrieved glyph for each second and third glyph identifier in the received compressed glyph string.

7. The method of claim 6 wherein step (a) further comprises the step of (a)(iv) repeating steps (a)(i) through (a)(iii) for each glyph in the glyph pattern string.

8. The method of claim 6 wherein step (b) further comprises the step of (b)(iv) repeating steps (b)(i) through (b)(iii) for each glyph in the received compressed glyph string.

9. The method of claim 6 wherein step (b) comprises:

(b) at the client workstation

(i) receiving the compressed glyph pattern string and, for each first glyph identifier, storing the glyph in a cache memory element indicated by the chunk parameter at an address determined from the assigned handle,

(ii) storing the assigned handle in a memory element determined by the subcache handle, and

(iii) generating a decoded string of glyphs by sequentially using each subcache handle to retrieve assigned handles, and using each handle and chunk parameter in the compressed glyph string for retrieving a corresponding stored glyph and substituting a retrieved glyph for each second and third glyph identifier in the received compressed glyph string.

10. The method of claim 8 wherein step (b)(i) further comprises receiving the compressed glyph pattern string and, for each first glyph identifier, storing the glyph in a cache memory element indicated by the glyph data size indicator at a memory element identified by multiplying the given prescribed size and the assigned handle.

11. A system for the lossless bandwidth compression encoding and decoding of data, the encoded data for transmission from an application server to a client workstation over a common transport mechanism in a distributed process system, the data represented as a glyph pattern string comprising a plurality of glyphs, the system comprising:

(a) an application server assigning a unique handle and a subcache handle to a glyph, and generating and transmitting to the client workstation a compressed glyph pattern string by placing into the compressed glyph pattern string;

a first glyph identifier upon a first occurrence of the glyph in the glyph pattern string, the first glyph identifier comprising;

(i) the glyph,

(ii) the assigned handle,

(iii) an assigned subcache handle, and

(iv) a chunk parameter indicating the number of bytes required to store the glyph;

a second glyph identifier when the glyph has previously occurred in the glyph pattern string and the assigned handle is not one of a predetermined number of handles stored in a cache memory, the second glyph identifier comprising;

(i) the assigned handle,

(ii) the assigned subcache handle, and

(iii) a chunk parameter indicating the number of bytes required to store the glyph;

a third glyph identifier when the glyph has previously occurred in the glyph pattern string and the assigned handle is one of a predetermined number of handles stored in a cache memory, the third glyph identifier comprising;

(i) the assigned subcache handle, and

(ii) a chunk parameter indicating the number of bytes required to store the glyph;

(b) a client workstation receiving the compressed glyph pattern string and, for each received first glyph identifier, storing the glyph in a memory element indicated by the chunk parameter at an address determined from the assigned handle, the client workstation generating a decoded string of glyphs by sequentially using each subcache handle to retrieve an assigned handle and using each retrieved assigned handle to retrieve a glyph from the memory element, and substituting a retrieved glyph for each second and third glyph identifier in the compressed glyph pattern string.

12. The system of claim 11 wherein the compressed glyph pattern string is prepared by the application server for transmission to the client workstation by incorporating the compressed glyph pattern string into a virtual channel supported by a normal communication protocol of the distributed process system.

13. The system of claim 11 wherein the client workstation further comprises a set of logical glyph memories, the client workstation storing in each logical glyph memory glyphs of a single size category.

14. The system of claim 11 wherein the address for a glyph stored in a logical glyph memory designated for storing glyph patterns of a given prescribed size is the product of the given prescribed size and the assigned handle.