Active pixel determination for line generation in regionalized rasterizer displays

• US 20030076325A1
• Filed: 10/18/2001
• Published: 04/24/2003
• Est. Priority Date: 10/18/2001
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Thrasher, Thomas L.
• Granted Patent: US 6,788,301 B2
• Time in Patent Office: Days
• US Class Current: 345/443
• CPC Class Codes: G06T 11/203 Drawing of straight lines or curves

Abstract

In one embodiment, selecting a pixel in a screen region on a screen of a monitor of a computer graphics display system to activate in rendering a straight line segment by a rasterizer assigned to the screen region. Steps of aligning a rectangular grid to pixel boundaries, wherein the screen comprises a screen space divided into at least one screen region, wherein the screen region comprises multiple pixels, identifying each pixel in the screen region through which the straight line segment passes, and selecting each identified pixel to activate for rendering the straight line segment on the screen when the straight line segment passes through a diamond shaped area of the pixel whose boundary is defined by the lower, upper, left, and right pixel grid mid-points are disclosed.

Claims

1. A method for selecting a pixel in a screen region on a screen of a monitor of a computer graphics display system to activate in rendering a straight line segment by a rasterizer assigned to the screen region, the method comprising the steps of:

aligning a rectangular grid to pixel boundaries, wherein the screen comprises a screen space divided into at least one screen region, wherein the screen region comprises multiple pixels;

identifying each pixel in the screen region through which the straight line segment passes; and

selecting each identified pixel to activate for rendering the straight line segment on the screen when the straight line segment passes through a diamond shaped area of the pixel whose boundary is defined by the lower, upper, left, and right pixel grid mid-points, wherein the pixel grid midpoints are the midpoints of the pixel boundaries.

2. The method as recited in claim 1, further comprising the method step of illuminating the pixel on the screen.

3. The method as recited in claim 1, wherein a locus of the straight line segment is specified by equation A*x+B*y+C=0, wherein A, B, and C are respectively a first, second, and third constants, wherein x and y are respectively Cartesian coordinate system x-axis and y-axis values of points on the straight line segment, and wherein the step of selecting each pixel to activate further comprises the steps of:

marking the pixel as other than selected;

setting a control variable equal to a preselected value;

for each pixel grid mid-point of the pixel grid,

while the pixel is marked as other than selected,

multiplying the first constant by the x-axis coordinate of the pixel grid mid-point;

multiplying the second constant by the y-axis coordinate of the pixel grid mid-point;

adding the third constant, the result of the method step of multiplying the first constant by the x-axis coordinate of the pixel grid mid-point, and the result of the method step of multiplying the second constant by the y-axis coordinate of the pixel grid mid-point; and

when the control variable is equal to the preselected value,

storing in a memory the algebraic sign of the result of the method step adding the third constant; and

setting the control variable to a value other than the preselected value;

otherwise, when the algebraic sign of the result of the method step adding the third constant differs from the stored algebraic sign,

marking the pixel as selected.

4. The method as recited in claim 1, wherein a locus of the straight line segment is specified by equation A*x+B*y+C=0, wherein A, B, and C are respectively a first, second, and third constants, wherein x and y are respectively Cartesian coordinate system x-axis and y-axis values of points on the straight line segment, and wherein the step of selecting each pixel to activate further comprises the steps of:

successively selecting once each pixel grid mid-point of the pixel grid until the pixel is marked as selected;

evaluating expression A*x+B*y+C at the pixel grid mid-point,

storing in a memory the algebraic sign of the evaluated expression for the selected pixel grid mid-point, and

if the algebraic sign of the evaluated expression for the selected pixel grid mid-point differs from the stored algebraic sign, marking the pixel as selected.

5. A program storage medium readable by a computer, tangibly embodying a software program of instructions executable by the computer to perform method steps for selecting a pixel in a screen region of a screen on a monitor of a computer graphics display system to activate in rendering a straight line segment by a rasterizer assigned to the screen region, the method steps comprising:

aligning a rectangular grid to pixel boundaries, wherein the screen comprises a screen space divided into at least one screen region, wherein the screen region comprises multiple pixels;

identifying each pixel in the screen region through which the straight line segment passes; and

selecting each identified pixel to activate for rendering the straight line segment on the screen when the straight line segment passes through a diamond shaped area of the pixel whose boundary is defined by the lower, upper, left, and right pixel grid mid-points, wherein the pixel grid midpoints are the midpoints of the pixel boundaries.

6. The program storage medium as recited in claim 5, further comprising the method step of illuminating the pixel on the screen.

7. The program storage medium as recited in claim 5, wherein a locus of the straight line segment is specified by equation A*x+B*y+C=0, wherein A, B, and C are respectively a first, second, and third constants, wherein x and y are respectively Cartesian coordinate system x-axis and y-axis values of points on the straight line segment, and wherein the step of selecting each pixel to activate further comprises the steps of:

marking the pixel as other than selected;

setting a control variable equal to a preselected value;

for each pixel grid mid-point of the pixel grid,

while the pixel is marked as other than selected,

multiplying the first constant by the x-axis coordinate of the pixel grid mid-point;

multiplying the second constant by the y-axis coordinate of the pixel grid mid-point;

adding the third constant, the result of the method step of multiplying the first constant by the x-axis coordinate of the pixel grid mid-point, and the result of the method step of multiplying the second constant by the y-axis coordinate of the pixel grid mid-point; and

when the control variable is equal to the preselected value,

storing in a memory the algebraic sign of the result of the method step adding the third constant; and

setting the control variable to a value other than the preselected value;

otherwise, when the algebraic sign of the result of the method step adding the third constant differs from the stored algebraic sign,

marking the pixel as selected.

8. The program storage medium as recited in claim 5, wherein a locus of the straight line segment is specified by equation A*x+B*y+C=0, wherein A, B, and C are respectively a first, second, and third constants, wherein x and y are respectively Cartesian coordinate system x-axis and y-axis values of points on the straight line segment, and wherein the step of selecting each pixel to activate further comprises the steps of:

successively selecting once each pixel grid mid-point of the pixel grid until the pixel is marked as selected;

evaluating expression A*x+B*y+C at the pixel grid mid-point,

storing in a memory the algebraic sign of the evaluated expression for the selected pixel grid mid-point, and

if the algebraic sign of the evaluated expression for the selected pixel grid mid-point differs from the stored algebraic sign, marking the pixel as selected.