[OpenLayers-Dev] OpenLayers.Control.OverviewMap or deeper

Tim-Hinnerk Heuer th.heuer at gmail.com
Sun Sep 2 20:10:29 PDT 2012

Hi List,

We have encountered a potential bug in OpenLayers:

When using GeoExt Panels and expanding a right hand side panel, the
overview map moves. When one then uses the OverviewMap control by clicking
on it, it behaves strangely in that the map is always zoomed to the left
(west) of where one clicked. I found out that it is a problem in the event

I fixed it by doing this:
I had to dig deep into the OpenLayers code to find the problem. Basically
the event system attaches an offset object (x,y) to the HTML element
(<div/>). It assumes though that the element does not move and only changes
this object when it changes. The overview map div, however, moves to the
left when the right hand side panel is opened. I did suspect early on that
this is the case but had to do some research as to where this happens and
how to find a fix for it. The fix I applied was to delete the offset object
whenever the rhs panel is expanded or collapsed. This seems to be a
fundamental flaw in OpenLayers that map elements are assumed to not move on
the page, because they definitely can when doing dynamic things with

>From Events.js:
    getMousePosition: function (evt) {
        // ...
        if (!this.element.offsets) {
            this.element.offsets =

Now, I couldn't think of a good fix for this yet, because we don't want to
recalculate the position every time for every element. I guess that is why
the condition is there:
if (!this.element.offsets) {
but I couldn't yet think of how to reset this or under which condition, at
least not in a generic way. Is there a move event for html elements which
could be listened for or something along those lines?

Thanks for reading.


Tim-Hinnerk Heuer

Twitter: @geekdenz
Blog: http://www.thheuer.com
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