- From: Charles Pritchard <chuck@jumis.com>
- Date: Fri, 31 Dec 2010 17:19:32 -0800
Implementation issues with the Drawing Model [1] have been floating around for some time. For whatever reasons, Microsoft is not willing to publicly discuss their issue with the spec, beyond the scant details listed below. That's fine and all.. I'm bringing it to the WHATWG's attention because it seems to me like some of the confusion could be avoided were a "standard" PNG photo available, demonstrating proper behavior. I thought this issue was resolved some time ago, but it keeps coming up. I don't fault anyone, it's a very subtle part of the spec. This reference image helped me communicate with Robert (Mozilla) last year, about the drawing model section. Screen cap: http://imgur.com/zUu66.png Generated from: https://developer.mozilla.org/en/Canvas_tutorial/Compositing Thread: http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-December/024316.html There seems to still be some disagreement over composting: https://bugs.webkit.org/show_bug.cgi?id=39177 I thought we had a handle on this, following some slight changes to the spec by Ian: http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-October/023706.html Apparently it's not handled yet. Sending out a flare, hoping that we can get this issue put to rest before the next round of major releases. -Charles Below are the only public comments I'm aware of, that MS has posted on the issue: http://lists.w3.org/Archives/Public/public-canvas-api/2010OctDec/0070.html Earlier thread... http://lists.w3.org/Archives/Public/public-canvas-api/2010AprJun/0046.html These comments lack the detail necessary to provide feedback. -------- Original Message -------- Subject: RE: Inconsistent behaviour of globalCompositeOperation property Resent-Date: Wed, 15 Dec 2010 23:47:24 +0000 Resent-From: public-canvas-api at w3.org Date: Wed, 15 Dec 2010 23:45:39 +0000 From: Jatinder Mann <jmann@microsoft.com> To: public-canvas-api at w3.org <public-canvas-api at w3.org> We initially felt that the Drawing Model [1], as written in the spec, was incorrectly defined. We have since consulted with many graphics experts, and it appears that the spec as written, and implemented by Firefox and Opera, is the correct definition of Porter-Duff and composition operations, and its behavior is acceptable. Thanks, Jatinder [1] http://dev.w3.org/html5/2dcontext/#drawing-model Jatinder Mann | Microsoft Program Manager | jmann at microsoft.com <mailto:jmann at microsoft.com> *From:*public-canvas-api-request at w3.org [mailto:public-canvas-api-request at w3.org] *On Behalf Of *Jatinder Mann *Sent:* Tuesday, May 25, 2010 11:57 AM *To:* public-canvas-api at w3.org *Subject:* Inconsistent behaviour of globalCompositeOperation property As we were reviewing the globalCompositeOperation property [1] of the Canvas 2D Context, we have noticed that there is a large inconsistency with the way web browsers implement this property. Firefox 3.6.3 and Opera 10.5 have a similar behaviour that matches the current version of the Canvas 2D Context spec. Chrome 4.1 and Safari 4.0.5 behave similarly to each other, albeit differently from the spec. Today, web developers cannot reliably use this property in designing their webpages due to this interoperability issue. We consider that the Safari implementation of the Drawing Model makes more sense from a web developer point of view. Most of the Canvas APIs are applied to the next primitive being drawn. However, the clipping behavior, as defined in the current Drawing Model [2], affects the current contents of the Canvas outside of the current primitive being drawn. The Safari Drawing Model calls for the clipping region to only affect the current primitive being drawn. We recommend updating the spec to match the Safari Drawing Model. We would like to discuss this area in more detail. Thank you, Jatinder [1] http://dev.w3.org/html5/2dcontext/#compositing [2] http://dev.w3.org/html5/2dcontext/#drawing-model Jatinder Mann | Microsoft Program Manager | jmann at microsoft.com <mailto:jmann at microsoft.com> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.whatwg.org/pipermail/whatwg-whatwg.org/attachments/20101231/8bef042b/attachment-0001.htm>
Received on Friday, 31 December 2010 17:19:32 UTC