[ka-Map-users] Opacity control in legend

Jacob Delfos jacob.delfos at maunsell.com
Thu Jun 16 01:01:39 EDT 2005

Hi Paul,

I gave it a try, but it's pretty hard. I actually tried to implement the sliding bar solution on 

It looks like a good solution, and it has a "slider stopfunction", which could invoke the setLayerOpacity function.

Problem I ran into is.... The content of the cells in the legend is written to it dynamically. I'm having a hard time getting the functions of the slider library to write a sliding bar into that legend cell. I assigned an ID to the legendcell, like:


Then I pass the name of the cell into the function that builds the slider, which I modified, to write to the object of which the name was parsed using innerHTML (rather than to document.write). But it doesn't work, and firefox won't tell me why. It's probably a bit too complex. I'm not exactly a DOM expert, either. 

By the way, the getcjs.php functionality makes it really hard to debug (everything occurs on line 1!). Can it have a parameter that makes it do nothing to the .js file, for debugging purposes? The "compress=no" option doesn't seem to do it....

-----Original Message-----
From: Paul Spencer [mailto:pspencer at dmsolutions.ca] 
Sent: 15 June 2005 20:32
To: Delfos, Jacob
Cc: ka-map-users at lists.maptools.org
Subject: Re: [ka-Map-users] Opacity control in legend


I've actually changed the CVS version to use a legend that is built 
entirely on the client side (it looks and works the same but is much 
better performance so far).  In the process, I took out the opacity 
control from the layers in the legend because I don't think this is a 
generally useful function ... in its place, I've set it up to read 
opacity from the metadata of the first layer in each group and use that 
to set the opacity of each group of layers.

It would be reasonably easy to modify kaLegend.js to add back in some 
form of layer opacity control.  Ideally, it would be some sort of slider 
I guess ...  I've played around with the Walter Zorn libraries for 
drawing and dragging, they work well.

If you have a real need for this, you could probably add an opacity 
control reasonably easily by modifying kaLegend.js to build the 
additional images and event handlers to replicate the original way that 
I had implemented this.

I may have time to add some sort of sliding opacity controller as an 
option while at MUM3 ... in between a few beers, I suspect ;)



Delfos, Jacob wrote:
> Hi all,
> I'm trying to put together a site that makes use of the opacity setting 
> in the legend, but it seems that the CVS version is not configured to 
> make use if it by default. I'm having some trouble figuring out how it 
> all fits together. The transparency sits in legend_template.php, which 
> uses legend_template.html. But how do I get the site to use it? I tried 
> modifying kaLegend.js, but that didn't do the trick.
> Paul.... How did you do it? :)
> Regards,
> Jacob
> *Maunsell Australia Pty Ltd
> 629 Newcastle Street, Leederville, WA 6007
> PO Box 81, Leederville, WA 6902
> Western Australia
> ABN 20 093 846 925
> Tel     + 61 8 9281 6185
> Fax    + 61 8 9281 6297
> _jacob.delfos at maunsell.com_
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|Paul Spencer                           pspencer at dmsolutions.ca   |
|Applications & Software Development                              |
|DM Solutions Group Inc                 http://www.dmsolutions.ca/|
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