Apparatus and method for processing graphical information to minimize page crossings and eliminate processing of information outside a predetermined clip window

• US 5,079,545 A
• Filed: 01/13/1989
• Issued: 01/07/1992
• Est. Priority Date: 01/13/1989
• Status: Expired due to Fees

• Current Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Priem, Curtis, Malachowsky, Chris
• Primary Examiner(s): Weldon, Ulysses
• Assistant Examiner(s): Fatahiyar, M.
• Application Number:
  US07/297,604
• Time in Patent Office: 1,089 Days
• Field of Search: 340/720, 340/721, 340/723, 340/724, 340/734, 340/747, 364/518, 364/521
• US Class Current: 345/628
• CPC Class Codes: G06T 15/30 Clipping

Abstract

An apparatus and method for processing graphical information in a manner such that 1) accesses to a frame buffer in which the graphical information is to be stored result in a minimum of page crossings in the frame buffer; and 2) time spent processing graphical information outside a predetermined clip window is minimized. These two goals are sometimes conflicting and the present invention determines how the graphical information should be processed so that frame buffer accesses are always performed with the least overhead. For a given object which is to be displayed within a defined window, by determining the portions of the object which are inside the window and the portions which are outside the window, it frequently is possible to determine whether the object should be drawn from top to bottom, bottom to top, left to right or right to left so as to minimize page crossings and minimize the time spent processing portions of the object outside a predetermined clip window.

Claims

1. An apparatus for generating comparisons between pairs of X and Y coordinates of an object to be displayed by a graphics subsystem, said object being one of a quadrilateral to be drawn and a block image to be moved, said apparatus having a clip window with predetermined top, bottom, right and left clip coordinates, and a test window with predetermined X and Y offsets from said top and bottom, and from said right and left, said object coordinates, said clip coordinates and said offsets for use in calculations for performing clipping of the object prior to its display, said apparatus comprising:

a) loading means for loading i) a plurality of object coordinate registers with said object coordinates, ii) a plurality of clip coordinate registers with said clip coordinates, and iii) a plurality of offset registers with said predetermined offsets;

b) comparison means coupled to said loading means for generating said comparisons;

c) calculation means coupled to said offset registers and said clip coordinate registers for calculating the borders of said test window relative to the borders of said clip window;

d) multiplexor means for selecting predetermined ones of said comparisons;

e) registers means for storing the selected predetermined ones of said comparisons;

f) comparison control means for controlling the operation of said comparison means, said multiplexor means and said register means

g) status generation means coupled to said register means for generating signals based upon certain of said selected predetermined ones of said comparisons which specify whether to minimize page crossings and eliminate the processing of clipped pixels, the object, if a quadrilateral, should be drawn in one of the directions of increasing X and decreasing X and in one of the directions of increasing Y and decreasing Y.

2. An apparatus for generating comparisons between pairs of X and Y object coordinates of an object to be displayed by a graphics subsystem, said object being one of a quadrilateral to be drawn and a block image to be moved, said apparatus having a clip window with predetermined top, bottom, right and left clip coordinates, and a test window with predetermined X and Y offsets from said top and bottom, and from said right and left, said objects coordinates, said clip coordinates and said offsets for use in calculations for performing clipping of the object prior to its display, said apparatus comprising:

a) loading means for loading i) a plurality of object coordinate registers with said object coordinates, ii) a plurality of clip coordinate registers with said clip coordinates, and iii) a plurality of offset registers with said predetermined offsets;

b) comparison means coupled to said loading means for generating said comparisons;

c) calculation means coupled to said offset registers and said clip coordinate registers for calculating the borders of said test window relative to the borders of said clip window;

d) multiplexor means for selecting predetermined ones of said comparisons;

e) register means for storing the selected predetermined ones of said comparisons;

f) comparison control means for controlling the operation of said comparison means, said multiplexor means and said register means;

g) status generation means coupled to said register means for generating signals based upon certain of said selected predetermined ones of said comparisons which specify whether, to minimize page crossings and eliminate the processing of clipped pixels, the object, if a block image to be moved, should be moved in one of the directions of increasing X and decreasing X and in one of the directions of increasing Y and decreasing Y.