[whatwg] CanvasRenderingContext2D.lineTo compatibility problem
Oliver Hunt
oliver at apple.com
Sat Jul 11 15:41:38 PDT 2009
While investigating a compatibility issue with http://www.blahbleh.com/clock.php
I found that the spec behaviour on CanvasRenderingContext2D.lineTo
conflicts with what Gecko implements.
The current spec language is
"The lineTo(x, y) method must do nothing if the context has no
subpaths. Otherwise, it must connect the last point in the subpath to
the given point (x, y) using a straight line, and must then add the
given point (x, y) to the subpath."
Gecko appears to treat the empty path case as moveTo(x,y). I'm going
to do a bit more investigation into the behaviour of this and the
other path manipulation functions to see whether lineTo is "special"
or this logic effects every function (of course any Gecko devs may be
able to answer more quickly than i can manually verify). On the
*assumption* that my initial analysis is correct i propose that the
language be updated to something akin to:
The lineTo(x, y) method is equivalent to moveTo(x, y) if the context
has no subpaths. Otherwise, it must connect the last point in the
subpath to the given point (x, y) using a straight line, and must then
add the given point (x, y) to the subpath.
--Oliver
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