Pick correlation

• US 5,491,494 A
• Filed: 11/19/1993
• Issued: 02/13/1996
• Est. Priority Date: 11/19/1993
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Mark, Edward F., Cornett, Kevin B.
• Primary Examiner(s): Weldon, Ulysses
• Application Number:
  US08/155,962
• Time in Patent Office: 816 Days
• Field of Search: 395/134, 395/143, 382/41, 382/48, 345/118, 345/145
• US Class Current: 345/622
• CPC Class Codes: G06F 3/04842 Selection of displayed objects or displayed text elements G06F3/0482 takes precedence

Abstract

A pick correlation method, comprises the steps of displaying a pick marker on a display screen; directing the pick marker at an image on the display screen, the image comprising at least one line primitive, and the pick marker having a pick window corresponding thereto; subjecting the at least one line primitive to a trivial test, whereby the at least one line primitive can be trivially tested by the trivial test if the at least one line primitive has both of its end-points outside of the same extended edge of the rectangular shaped pick window and, if successfully tested by the trivial test, accepting or rejecting the at least one line primitive in accordance with the results of the trivial test; and if the at least one line primitive cannot be trivially tested, subjecting the at least one line primitive to a non-trivial test which does not require performing floating point operations, and accepting or rejecting the at least one line primitive in accordance with the results of the non-trivial test.

Claims

1. In a computer graphics system, a method of selecting an object from a plurality of objects displayed on a computer graphics display in response to a user initiated pick selection, each of said plurality of objects comprising at least one line primitive having end-point coordinates, said method comprising the steps of:

(a) displaying a pick marker in a first position on said computer graphics display of said computer graphics system, said pick marker having a rectangular shaped pick window corresponding thereto;

(b) providing an input device for controlling movement of said pick marker within said computer graphics display;

(c) manipulating said input device for repositioning said pick marker to a second position within said computer graphics display, such that said pick marker is directed at a selected one of said plurality of objects displayed on said computer graphics display;

(d) inputting with said input device a signal effectuating selection of said selected object, wherein the selection is determined according to the steps of;

subjecting each line primitive of each object displayed on said computer graphics display to a trivial test, whereby said trivial test is capable of testing line primitives having both end-points outside of the same extended edge of said rectangular shaped pick window, and accepting or rejecting line primitives in accordance with the results of said trivial test;

subjecting line primitives which are incapable of being tested by said trivial test to a non-trivial test, said non-trivial test comprising the steps of transforming the coordinates of said rectangular shaped pick window such that its center is at the origin coordinates and transforming the coordinates of the line primitive in accordance with and relative to the transformed coordinates of said rectangular shaped pick window, comparing a threshold value based on end-point coordinates of the line primitive with a product-sum based on the height and width of said rectangular shaped pick window and end-point coordinates of the line primitive, and accepting the line primitive if the threshold value is less than or equal to the product-sum; and

(e) subjecting the object corresponding to line primitives accepted during said trivial or non-trivial test to further computer processing.

2. A method according to claim 1, wherein said trivial test in step (d) is further capable of testing said at least one line primitive if said at least one line primitive has either one or both of its end-points visible within said rectangular shaped pick window, or has its end-points in opposite outer, non-extended edge regions relative to said rectangular shaped pick window.

3. A method according to claim 2, wherein said trivial test in step (d) comprises an enhanced version of the Cohen-Sutherland test.

4. A method according to claim 3, wherein said non-trivial test in step (d) includes the step of determining if the line primitive satisfies either the condition that |h*dx+w*dy|>

=|T| or the condition that |h*dx-w*dy|>

=|T|, wherein x₁, y₁ and x₂, y₂ are end-point coordinates of the line primitive;

T is the threshold value;

dx=x₁ -x₂ ;

dy=y₁ -y₂ ; and

T=x₁ *y₂ -y₁ *x₂ =y₁ *dx-x₁ *dy;

wherein the line primitive is accepted if the line primitive satisfies either of said conditions.

5. A method according to claim 1, wherein said trivial test in step (d) comprises the Cohen-Sutherland test.

6. A method according to claim 5, wherein said non-trivial test in step (d) includes the step of determining if the line primitive satisfies either the condition that |h*dx+w*dy|>

=|T| or the condition that |h*dx-w*dy|>

=|T|, wherein x₁, y₁ and x₂, y₂ are end-point coordinates of the line primitive;

T is the threshold value;

dx=x₁ -x₂ ;

dy=y₁ -y₂ ; and

T=x₁ *y₂ -y₁ *x₂ =y₁ *dx-x₁ *dy;

wherein the line primitive is accepted if the line primitive satisfies either of said conditions.

7. A method according to claim 1, wherein said non-trivial test in step (d) includes the step of;

determining if the line primitive satisfies either the condition that |h*dx+w*dy|>

=|T| or the condition that |h*dx-w*dy|>

=|T|, wherein x₁, y₁ and x₂, y₂ are end-point coordinates of the line primitive;

T is the threshold value;

dx=x₁ -x₂ ;

dy=y₁ -y₂ ; and

T=x₁ *y₂ -y₁ *x₂ =y₁ *dx-x₁ *dy;

wherein the line primitive is accepted if the line primitive satisfies either of said conditions.