Method for the lossless compression of lines in a distributed computer system

• US 6,057,857 A
• Filed: 06/12/1996
• Issued: 05/02/2000
• Est. Priority Date: 06/12/1996
• Status: Expired due to Term

• Current Assignee: Citrix Systems, Inc. (Cloud Software Group)
• Original Assignee: Citrix Systems, Inc. (Cloud Software Group)
• Inventors: Bloomfield, Marc A.
• Primary Examiner(s): Hong, Stephen S.
• Application Number:
  US08/662,590
• Time in Patent Office: 1,420 Days
• Field of Search: 345/423, 345/441, 345/442, 345/443, 345/144, 345/468, 345/469, 345/135, 382/241, 382/242, 382/244
• US Class Current: 345/441
• CPC Class Codes: G06T 9/001 Model-based coding, e.g. wire frame
• CPC Class Codes: G06T 9/20 Contour coding, e.g. using detection of edges

Abstract

In a distributed computer system, a method for lossless compression of a graphical line within an application server allows the compressed line data to be transmitted over a low bandwidth transport mechanism to a graphical user interface for display on a workstation. The application server determines, from graphical line data representative of the graphical line, coordinate locations for the endpoints of each sub-path of the graphical line and attributes of each sub-path. The application server generates a compressed line data packet of variable length which includes the coordinate location data and attribute data for each sub-path of the graphical line.

Claims

1. A method for the lossless compression of graphical line data for transmission over a low bandwidth communication transport mechanism to a graphical user interface of a workstation in a distributed computer system, the graphical line data representative of a graphical line to be displayed on a display screen of the workstation, comprising:

a) determining, from said graphical line data, coordinate locations for the endpoints of each sub-path of the graphical line;

b) determining, from said graphical line data, attributes of each sub-path;

c) representing said coordinate locations as compressed coordinate location data of variable length without any data loss of said coordinate locations;

d) representing said attributes as compressed attribute data of variable length without any data loss of said attributes;

e) determining, from said graphical line data, a flag indicator containing information applicable to at least one sub-path of the graphical line, said flag indicator identifying a state of at least one attribute, wherein said at least one attribute is selectively encoded as part of said compressed attribute data in accordance with said flag indicator; and

f) providing a compressed line data packet of variable length which includes said compressed coordinate location data, compressed attribute data, and flag indicator for each sub-path.

2. The method of claim 1 wherein the compress ed line data packet fully defines the characteristics of the graphical line.

3. The method of claim 1 wherein said attributes include clipping, style, gaps, color and type.

4. The method of claim 3 wherein said style of each sub-path is solid, alternate, dash, dot, dashdot, dashdotdot, mask or array.

5. The method of claim 3 wherein said type of each sub-path is normal, horizontal, vertical, diagonal or ellipse.

6. The method of claim 1, wherein the flag indicator identifies a state of at least one coordinate location.

7. The method of claim 1, wherein the flag indicator identifies a transitional state of at least one attribute between the current compressed line data packet and a previous compressed line data packet.

8. A method for the lossless compression of graphical line data for transmission over a low bandwidth communication transport mechanism to a graphical user interface of a workstation in a distributed computer system, the graphical line data including at least one sub-path and representative of a graphical line to be displayed on a display screen of the workstation, comprising:

a) determining, from said graphical line data, coordinate locations for the endpoints of each sub-path included in the graphical line data;

b) determining, from said graphical line data, attributes of each sub-path;

c) storing an attribute indicator in a compressed line data packet, said attribute indicator including information applicable to said at least one sub-path included in the graphical line data, wherein said attribute indicator identifies a state of at least one attribute that is selectively encoded as part of the compressed line data packet in accordance with said attribute indicator; and

d) storing a sub-path information field, including encoded endpoint information, in the compressed line data packet, wherein said compressed line data packet is fully reversible for said coordinate locations and attributes.

9. The method of claim 8 further comprising, before step (c), the step of storing a protocol indicator flag.

10. The method of claim 8 wherein the attribute indicator comprises information identifying the color of the graphical line data.

11. The method of claim 10 wherein the attribute indicator comprises a one bit field if the color of the graphical line data is the same as an immediately previous graphical line data.

12. The method of claim 10 wherein the attribute indicator comprises a one byte field if the color of the graphical line data is different from an immediately previous graphical line data, the one byte field encoding the color of the current graphical line data.

13. The method of claim 8 wherein the attribute indicator comprises information identifying the style of the graphical line data.

14. The method of claim 8 wherein the attribute indicator comprises clipping information for the graphical line data.

15. The method of claim 8 further comprising the step of transmitting the compressed line data packet.

16. The method of claim 8, wherein the attribute indicator identifies a transitional state of at least one attribute between the current compressed line data packet and a previous compressed line data packet.