RE: Adding winding rules to Canvas

> As you may know until now, canvas only supported even-odd winding.

> Maybe graphics libraries and SVG also support non-zero winding.

Actually, Canvas 2D Context Level 1 only supports the non-zero winding rule for fill(), clip(), and isPointInPath() today, not even-odd rule.

> I have the following proposal:

> enum CanvasWindingRule { "nonzero", "evenodd" };
> void fill(optional CanvasWindingRule w = "nonzero");
> void clip(optional CanvasWindingRule w = "nonzero");
> boolean isPointInPath(unrestricted double x, unrestricted double y, optional CanvasWindingRule w = "nonzero");



It's great to see a proposal here. I strongly feel we should allow developers to select either non-zero winding rule or even-odd rule, just like other graphics technologies. I prefer this proposal instead of introducing new functions for developers to learn, e.g., eoFill(), eoIsPointInPath(), and eoClip().



I believe we will also need to extend this feature to the following versions of those functions as well:



void fill(Path path, optional CanvasWindingRule w = "nonzero");

void clip(Path path, optional CanvasWindingRule w = "nonzero");

boolean isPointInPath(Path path, unrestricted double x, unrestricted double y, optional CanvasWindingRule w = "nonzero");



Thanks,

Jatinder

From: Rik Cabanier [mailto:cabanier@gmail.com]
Sent: Tuesday, January 15, 2013 12:43 PM
To: public-canvas-api@w3.org
Subject: Adding winding rules to Canvas

All,

there was a recent discussion on adding winding rules to canvas. As you may know until now, canvas only supported even-odd winding.
Maybe graphics libraries and SVG also support non-zero winding.[1][2]

Mozilla exposes this currently with 'mozFillRule'. Making this part of the graphics state has several drawbacks.
The biggest is that fill/clip will now have to check the state every time, or set/reset it. Winding is also part of path geometry.

I have the following proposal:
enum CanvasWindingRule { "nonzero", "evenodd" };
void fill(optional CanvasWindingRule w = "nonzero");
void clip(optional CanvasWindingRule w = "nonzero");
boolean isPointInPath(unrestricted double x, unrestricted double y, optional CanvasWindingRule w = "nonzero");

proposed patches for this API can be found here:
https://bugs.webkit.org/show_bug.cgi?id=105508
https://bugzilla.mozilla.org/show_bug.cgi?id=827053

What do people think?

1: http://www.w3.org/TR/SVG/painting.html#FillRuleProperty
2: http://en.wikipedia.org/wiki/Nonzero-rule