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Use case for SVG + HTML : Making puzzle

From: Jeremie Patonnier <jeremie.patonnier@gmail.com>
Date: Thu, 9 Sep 2010 00:40:42 +0200
Message-ID: <AANLkTin9M6_q7hLDP+9SMZg2k5i1UFS5AUifmAdq=8Ct@mail.gmail.com>
To: www-svg@w3.org

I would to show you this demo I made in July :

XHTML : http://jeremie.patonnier.net/experiences/svg/inline/puzzle.en.xhtml
HTML 5 : http://jeremie.patonnier.net/experiences/svg/inline/puzzle.en.html

(for those of you who speak French, I have write a full article about this
demo :

Right at the moment, this demo only work with Firefox 4 beta and Firefox 3.6
(in XHTML mode only)

This demo allow you to turn any image or video into a Jigsaw Puzzle.
Basically, each pieces of the puzzle is a SVG element that embed a canvas
element, cut off by a SVG clipPath.

What's failing in Opera and Chrome (I have not tested with IE9 yet)

1. Black pieces

Opera and Chrome display black pieces. This is because of Firefox bug
Firefox does not follow the spec on how CSS have to be handled with the SVG
'use' element. So my CSS rules are bad but work with FF.

2. Filters on HTML elements

If you activate the option "Show hint", with Firefox, you'll see a grayed
version of the image/video. With other browser you'll see the normal
image/video. This is because only Firefox support SVG filters on HTML
element (I apply a color matrix over a canvas element). This use case (a
filter applied to a canvas) is very useful because you can change the output
rendering of the canvas without touching its pixels definitions and keep it
clean for further manipulation.

3. Pointer-events handling

Pointer-events allow me to make the piece dragable only when you click on a
visible part of a piece thanks to the way clipPath handle pointer events.

Unfortunately, no browser handle pointer-events property the same way.

With Firefox, I have to disable the pointer-events on the main SVG element
and re-enable it on the canvas element. If I don't do this, FF does not
honor the clipPath rule for the pointer events and fire a pointer event even
on none visible part of the image.

The problem with Opera is that it does not re-enable the events on the
canvas, so you can't drag the pieces (I guess that it's because it does not
handle pointer-events property on HTML elements... I have not tested it in
detail yet)
The problem with Chrome is that even with this disable/enable trick it does
not honor the clipPath rule for pointer events so you can start draging a
piece even on a invisible par of it.

Those three points are the main problems I have to deal with to make this
demo truly cross-browser. But there are other concerns. For example, at that
moment, I must create a canvas for each piece which has a serious hit on
performance, especially with video. It is a true use case where using the
SVG 'use' element to duplicate a single canvas context among multiple "fake"
canvas element could be really helpful. Another tricky point (which is not
SVG nor HTML related) is the DOM getElementsByTagName property which is
buggy (or simply inconsistent) in almost every browser : Opera does not
understand "getElementsByTagNames('svg:svg')" (I have to use
getElementsByTagNameNS instead) ; Firefox and Chrome have problems with SVG
camel-case Tags in a HTML5 context (but I know they are working on it)

Best regards
Jeremie Patonnier
web : http://jeremie.patonnier.net
Twitter : http://twitter.com/JeremiePat
Received on Wednesday, 8 September 2010 22:41:14 UTC

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