910142 - <canvas>: the end point of canvas arc is incorrect.

Status: NEW

(Core :: Graphics: Canvas2D, defect)

Description

[Dongseong Hwang]

Attachment: various tests to cover extensive endAngle and startAngle

User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.14 Safari/537.36

Steps to reproduce:

Canvas spec defines start point and end point of arc as follows:

http://www.w3.org/TR/2dcontext2/#dom-context-2d-arc
The points at startAngle and endAngle along this circle's circumference, measured in radians clockwise from the ellipse's semi-major axis, are the start and end points respectively


Actual results:

When endAngle-startAngle is greater than 2π, the end point is the same to the start point regardless of the end angle.


Expected results:

End point of arc must be consistent with end angle

Comment 1

[Dongseong Hwang]

Blink had the same issue and fixed in https://codereview.chromium.org/18286007/

There is a discussion about it in W3C bugzilla: https://www.w3.org/Bugs/Public/show_bug.cgi?id=23050

Comment 2

[Milan Sreckovic [:milan] (needinfo for best results)]

I think this would just take an updated implementation of ArcToBezier (gfx/2d/PathHelpers.h).

Comment 3

[Hixie (not reading bugmail)]

I've updated the spec to say that Firefox's current behaviour is correct.
https://www.w3.org/Bugs/Public/show_bug.cgi?id=23050