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ISSUE: clientX and clientY coordinates in DOM MouseEvents

From: Thierry Kormann <tkormann@ilog.fr>
Date: Fri, 11 Jan 2002 06:02:58 -0500 (EST)
Message-Id: <200201111102.g0BB2J915621@quokka.inria.fr>
To: www-svg@w3.org
Cc: www-dom@w3.org
ISSUE: clientX and clientY coordinates in DOM MouseEvents

This following issue has been reported by Alex Fritze. I think this is a real
problem so I reported this issue as an official one to the SVG WG and the DOM
WG.

---

The DOM Level 2 specification defines two attributes clientX and clientY for
MouseEvents. According to the DOM Level 2 specification, those coordinates are
relative to the DOM Implementation's client area.

The SVG specification has changed this definition and the clientX and clientY
attributes represents viewport coordinates for the coresponding svg element.

In a multiple namespaces environment (such as mixing xhtml and svg for
example), there is a conflict with the two definitions above.

ex:

<html:div id="A">
  <svg:svg id="B" viewBox="0 0 10000 10000">
    <svg:circle id="C" />
    ...
   </svg:svg>
</html:div>

In that example, according to the DOM spec, clientX and clientY should be
relative to DOM Implementation's client area (i.e. the user agent area used 
to display the whole DOM tree).

According to the SVG spec, if a mouse event occured on B or C, clientX and
clientY should be relative to the viewport ([0, 0] [10000, 10000]) and this is
not what the DOM spec says.

The DOM specification clearly says that whatever the EventTarget is, clientX
and clientY must be relative to the user agent drawing area. Having the
correct behavior for both SVG and DOM is only possible in a plugin environment
(two separate DOM tree - two different user agent).

RECOMMENDATION:

[A]

Ask the DOM WG to errate the DOM Level 2 Events module and change the DOM
Level 3 Events module saying something like:

clientX - The horizontal coordinate at which the event occured relative to
coordinate system of the EventTarget.

clientY - The horizontal coordinate at which the event occured relative to
coordinate system of the EventTarget.

Advantage: that will not break any existing SVG content and should work with
all existing XML applications that have only one coordinate system: the user 
agent area's one.

Note: Some extra work will be necessary if both informations are needed (mouse
coordinates in the EventTarget's coordinate system and in the user agent's
area coordinate system) and I believe that both are usefull.

[B]

Add an errata to the SVG1.0 spec explaining that clientX and clientY have the
same behavior than in the DOM specification (and that will break existing SVG
content using clientX and clientY - that's to say, most of the dynamic SVG
content using scripting).

Ask the DOM WG to add two new coordinates 'viewportX' and 'viewportY' to the
MouseEvent interface in the DOM Level 3 Events module. SVG1.1 will have to
rely on that module.

- viewportX
  The horizontal coordinate at which the event occured relative to coordinate
  system of the EventTarget.

- viewportY
  The vertical coordinate at which the event occured relative to coordinate
  system of the EventTarget.


Any comments?

Thierry.
Received on Friday, 11 January 2002 11:24:25 GMT

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