- From: Oliver Hunt <oliver@apple.com>
- Date: Mon, 24 Sep 2007 14:47:07 -0700
Hi All, We've encountered a number of website compatibility issues in WebKit due to our adherence to the new Canvas specifications -- a good example of this is rect drawing at http://canvaspaint.org The most obvious issues can be shown if you use the draw rect tool and resize the rect repeatedly. The first problem is the repeated drawing of old rects, this is due to the context path not being cleared by draw rect and fill rect which is the behaviour present in Safari 2 and Firefox 2. While I've discussed the issue with Hixie in the past (and to an extent agree with him) the Firefox 3 nightlies do not appear to have adopted this behaviour, leaving us in a position where we have to choose between compatibility and compliance which is awkward. The second problem is that the rules for drawing rects/adding rects to the path require us to throw an exception on negative width/ height, once again Firefox 3 does not match this behaviour, putting us in a position where we need to choose between compatibility and compliance. In this case however it is relatively easy to make the argument that an exception should _not_ be thrown, as it means webapp developers either need to litter their code with exception handlers or add significant logic to ensure that their apps do not unexpectedly terminate. The possible responses to drawing a rect with negative dimensions are (excluding the unappealing exception behaviour currently defined) to cull/ignore them (as we do with 0-sized rects), to normalise them (the current behaviour of firefox, and the behaviour expected by those apps that are affected by it), or to normalise them and treat the negative dimensions as an implicitly reversing the winding direction. Both Opera and Safari 3 match the specification behaviour in both these cases, which results in multiple sites failing to render. Cheers, Oliver
Received on Monday, 24 September 2007 14:47:07 UTC