- From: Richard Schwerdtfeger <schwer@us.ibm.com>
- Date: Mon, 20 Jun 2011 17:45:21 -0500
- To: Frank Olivier <Frank.Olivier@microsoft.com>
- Cc: "chuck@jumis.com" <chuck@jumis.com>, Cynthia Shelly <cyns@microsoft.com>, "david.bolter@gmail.com" <david.bolter@gmail.com>, "Mike@w3.org" <Mike@w3.org>, "public-canvas-api@w3.org" <public-canvas-api@w3.org>, "public-html@w3.org" <public-html@w3.org>, "public-html-a11y@w3.org" <public-html-a11y@w3.org>, public-html-request@w3.org
- Message-ID: <OF10BDDCC1.5E4D644A-ON862578B5.0079CE2D-862578B5.007D0027@us.ibm.com>
I have some concerns about this. It means: - The author has to do the transformations - We have to add DOM attributes - The mouse events are routed to canvas and not the sub-DOM elements where the keyboard handling is going on. The user agent could process the mouse events at canvas and then propagate them to the corresponding DOM object in the subtree. Your proposal does have the advantage that the bounds of the objects are in the DOM but for HTML we don't have this for any of the DOM elements now. What I was thinking was the following: - Today Canvas has the notion of a context - We allow the author to have the same context (with methods) for each drawing object and apply a bounds and z-index as you suggest. - We then bind each drawing object to the canvas subtree DOM element: So each drawing object would be an instance of a canvas context with methods were we do something like: 1. we assume that the canvas element when the page is created is an instance of a canvasObject (having a context) 2. we assume that drawingOjects are a subclass of canvasObject that support all the canvas2DAPI in canvasObject with some additions such as: - ZIndex attribute - a bounding drawing path and methods for modifying them - a method for associating the drawingObject with a canvas subtree DOM element. 3. we add an method to canvas that says addDrawObject. On the canvas element we have the following: var canvas = document.getElementById(‘canvasTest’); if (canvas.getContext){ var ctx = canvas.getContext(’2d’); DO = new drawingObject(); dctx= DO.getContext('2d'); dctx.ZIndex="2"; dctx.beginPath(); dctx.moveTo(130,100); dctx.lineTo... ... dctx.setPathtoBounds(); dctx.setDOMSubtreeNode(foo); //Foo is a subtree node where keyboard events go to and we do our accessibility enablement to populate the accessibility tree //Internally the user agents maps the bounding rectangle for the accessible of the DOM object as a best fit rectangle of the //path used to form the bounds of the drawing object ctx.addDrawingObject(DO); } Now the user agent the information needed to do the hit testing and retained mode graphics (I am oversimplifying for illustration purposes) to be able to track the pointing device input and routing it to the same DOM objects that process the keyboard and all the other accessibility information. This includes hit testing. Mike provided feedback on the HTML A11Y call that authors did not want to do the hit testing themselves. Rich Schwerdtfeger CTO Accessibility Software Group From: Frank Olivier <Frank.Olivier@microsoft.com> To: Richard Schwerdtfeger/Austin/IBM@IBMUS, "chuck@jumis.com" <chuck@jumis.com>, "Mike@w3.org" <Mike@w3.org>, "david.bolter@gmail.com" <david.bolter@gmail.com>, Cynthia Shelly <cyns@microsoft.com> Cc: "public-canvas-api@w3.org" <public-canvas-api@w3.org>, "public-html-a11y@w3.org" <public-html-a11y@w3.org>, "public-html@w3.org" <public-html@w3.org> Date: 06/20/2011 11:01 AM Subject: RE: hit testing and retained graphics Sent by: public-html-request@w3.org I would leave hit testing up to the (javascript) author. I would recommend that they set existing x,y position, z-index attributes on the DOM objects in the canvas subtree to report what the UI 'looks like' to AT tools. This way, the AT tools don't need to change - this part of the DOM is no different to them than any other part - and authors need to be annotating canvas DOM objects with correct information anyway (labels, aria attributes, etc). From: Richard Schwerdtfeger [mailto:schwer@us.ibm.com] Sent: Friday, June 17, 2011 11:42 AM To: chuck@jumis.com; Frank Olivier; Mike@w3.org; david.bolter@gmail.com; Cynthia Shelly Cc: public-canvas-api@w3.org; public-html-a11y@w3.org; public-html@w3.org Subject: hit testing and retained graphics Charles, Frank, Mike, I am back from vacation. How far do we need to go with hit testing? Right now I am looking at associating a closed draw path with a DOM object in the canvas subtree. We would then need to address the routing of pointing device input events to the DOM object. The drawing path can be used to provide bound information to platform accessibility API. Do we need to bind any other drawing properties to the canvas object - similar to the way device context's are handled on graphic subsystems like Windows? Mike, I am including you as before I went on vacation you indicated that a number of developers desired this feature and wanted to be involved. Rich Rich Schwerdtfeger CTO Accessibility Software Group
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Received on Monday, 20 June 2011 22:46:02 UTC