DECOMPOSING CUBIC BEZIER SEGMENTS FOR TESSELLATION-FREE STENCIL FILLING

• US 20110285720A1
• Filed: 04/29/2011
• Published: 11/24/2011
• Est. Priority Date: 05/21/2010
• Status: Active Grant

• Current Assignee: NVIDIA Corporation
• Original Assignee: NVIDIA Corporation
• Inventors: KILGARD, Mark J.
• Granted Patent: US 8,730,253 B2
• Time in Patent Office: Days
• US Class Current: 345/442
• CPC Class Codes: G06T 11/203 Drawing of straight lines or curves
• CPC Class Codes: G06T 15/005 General purpose rendering architectures

Abstract

One embodiment of the present invention sets forth a technique for decomposing and filling cubic Bèzier segments of paths without tessellating the paths. Path rendering may be accelerated when a GPU or other processor is configured to perform the decomposition operations. Cubic Bèzier paths are classified and decomposed into simple cubic Bèzier path segments based on the classification. A stencil buffer is then generated that indicates pixels that are inside of the decomposed cubic Bèzier segments. The paths are then filled according to the stencil buffer to produce a filled path.

Claims

1. A method of decomposing cubic Bè

zier path segments, the method comprising;

receiving a path including a cubic Bè

zier path segment;

subdividing the cubic Bè

zier path segment into simple cubic Bè

zier path segments when the cubic Bè

zier path segment is classified as having a serpentine or loop topology;

assigning texture map coordinates to vertices of the simple cubic Bè

zier path segments that define a convex hull geometry; and

generating a stencil buffer indicating pixels that are inside of the cubic Bè

zier path segment by processing the texture map coordinates.

2. The method of claim 1, wherein the generating of the stencil buffer comprises processing an anchor geometry that is defined by an anchor point and a start vertex and an end vertex of a first simple cubic Bè

zier path segment of the simple cubic Bè

zier path segments.

3. The method of claim 2, wherein the generating of the stencil buffer comprises incrementing values of the stencil buffer corresponding to pixels covered by the anchor geometry when the anchor geometry is front-facing and decrementing the values of the stencil buffer corresponding to the pixels covered by the anchor geometry when the anchor geometry is back-facing.

4. The method of claim 1, wherein the generating of the stencil buffer comprises discarding pixels covered by the convex hull geometry based on a function of the texture map coordinates.

5. The method of claim 4, wherein the generating of the stencil buffer comprises incrementing values of the stencil buffer corresponding to surviving pixels covered by the convex hull geometry when the convex hull geometry is front-facing and decrementing the values of the stencil buffer corresponding to the surviving pixels covered by the convex hull geometry when the convex hull geometry is back-facing.

6. The method of claim 1, further comprising replacing a degenerate cubic Bè

zier path segment of the path with a quadratic Bè

zier path segment, a line segment, or a point.

7. The method of claim 1, wherein the generating of the stencil buffer comprises disabling writes to a depth buffer and a color buffer.

8. The method of claim 1, further comprising:

constructing a bounding geometry that encloses the path; and

rendering the bounding geometry and writing the color buffer based on the stencil buffer to fill pixels that are inside of the path.

9. The method of claim 1, wherein the subdividing of the cubic Bè

zier path segment comprises dividing the cubic Bè

zier path segment having a loop topology into a first simple cubic Bè

zier path segment and a second simple cubic Bè

zier path segment at a root point.

10. The method of claim 1, wherein the subdividing of the cubic Bè

zier path segment comprises dividing the cubic Bè

zier path segment having a serpentine topology into a first simple cubic Bè

zier path segment and a second simple cubic Bè

zier path segment at an intersection point of the cubic Bè

zier path segment and a base segment between a start vertex and an end vertex of the cubic Bè

zier path segment.

11. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to decompose cubic Bè

zier path segments, by performing the steps of;

receiving a path including a cubic Bè

zier path segment;

subdividing the cubic Bè

zier path segment into simple cubic Bè

zier path segments when the cubic Bè

zier path segment is classified as having a serpentine or loop topology;

assigning texture map coordinates to vertices of the simple cubic Bè

zier path segments that define a convex hull geometry; and

generating a stencil buffer indicating pixels that are inside of the cubic Bè

zier path segment by processing the texture map coordinates.

12. The non-transitory computer-readable storage medium of claim 11, wherein the generating of the stencil buffer comprises processing an anchor geometry that is defined by an anchor point and a start vertex and an end vertex of a first simple cubic Bè

zier path segment of the simple cubic Bè

zier path segments.

13. The non-transitory computer-readable storage medium of claim 12, wherein the generating of the stencil buffer comprises incrementing values of the stencil buffer corresponding to pixels covered by the anchor geometry when the anchor geometry is front-facing and decrementing the values of the stencil buffer corresponding to the pixels covered by the anchor geometry when the anchor geometry is back-facing.

14. The non-transitory computer-readable storage medium of claim 11, wherein the generating of the stencil buffer comprises discarding pixels covered by the convex hull geometry based on a function of the texture map coordinates.

15. The non-transitory computer-readable storage medium of claim 14, wherein the generating of the stencil buffer comprises incrementing values of the stencil buffer corresponding to surviving pixels covered by the convex hull geometry when the convex hull geometry is front-facing and decrementing the values of the stencil buffer corresponding to the surviving pixels covered by the convex hull geometry when the convex hull geometry is back-facing.

16. The non-transitory computer-readable storage medium of claim 11, further comprising replacing a degenerate cubic Bè

zier path segment of the path with a quadratic Bè

zier path segment, a line segment, or a point.

17. The non-transitory computer-readable storage medium of claim 11, further comprising:

constructing a bounding geometry that encloses the path; and

rendering the bounding geometry and writing the color buffer based on the stencil buffer to fill pixels that are inside of the path.

18. The non-transitory computer-readable storage medium of claim 11, wherein the subdividing of the cubic Bè

zier path segment comprises dividing the cubic Bè

zier path segment having a loop topology into a first simple cubic Bè

zier path segment and a second simple cubic Bè

zier path segment at a root point.

19. The non-transitory computer-readable storage medium of claim 11, wherein the subdividing of the cubic Bè

zier path segment comprises dividing the cubic Bè

zier path segment having a serpentine topology into a first simple cubic Bè

zier path segment and a second simple cubic Bè

zier path segment at an intersection point of the cubic Bè

zier path segment and a base segment between a start vertex and an end vertex of the cubic Bè

zier path segment.

20. A system for decomposing cubic Bè

zier path segments, the system comprising;

a memory that is configured to store a stencil buffer; and

a processor that is coupled to the memory and configured to;

receive a path including a cubic Bè

zier path segment;

subdivide the cubic Bè

zier path segment into simple cubic Bè

zier path segments when the cubic Bè

zier path segment is classified as having a serpentine or loop topology;

assign texture map coordinates to vertices of the simple cubic Bè

zier path segments that define a convex hull geometry; and

write values to the stencil buffer indicating pixels that are inside of the cubic Bè

zier path segment by processing the texture map coordinates.