Bug 16565 – CG Path Handling Seems Inverted

• Component: WebCore Misc.
• Status: RESOLVED INVALID

[Brent Fulgham]

The HTML5 specification indicates that arc is:
"void arc(in float x, in float y, in float radius, in float startAngle, in float endAngle, in boolean anticlockwise);"

This was originally code with the boolean being labeled "clockwise", which resulted in the Cairo back-end drawing 'flipped' arcs (see Bug#16558).

Review of the code indicates that this was simply a matter of improper label, however the CoreGraphics backend has the following mysterious behavior:

The 'addArc' method takes a bool previously labeled 'clockwise', but which is now known to actually mean 'anticlockwise' when triggered by a request to draw.  This flag is passed (unchanged) to the "CGPathAddArc" function, which is documented to expect this argument to mean 'clockwise' (not 'anticlockwise').

Consequently, I would expect the CG backend to be producing inverted drawings (however it does seem to produce the expected output).

Either:
1.  The CGPathAddArc method is improperly documented in the Apple API docs.
2.  The CG drawing context is flipped when finally rendering, resulting in a proper image.

[David Kilzer (:ddkilzer)]

<rdar://problem/5661165>

[Brent Fulgham]

The code as written is correct. The documentation issue is outside the scope of the WebKit project.