[OpenLayers-Dev] Problem with Alpha Layer

[Christopher Schmidt]

On Sat, Sep 29, 2007 at 08:41:02AM +0200, Jochen Grefe wrote:
> I have a problem with a layer (kamap in particular) with alpha set to
> true.

Just so you know:

alpha set to true is unlikely to be very useful to you. Unfortunately,
the one problem it is designed to fix -- transparency issues in IE -- is
a huge performance hit, because IE can't apply the image hack to images
that quickly.

So, you should probably not be using the alpha: true without careful
consideration.

> Perhaps I found the error in Util.js.
> 
> OpenLayers.Util.createAlphaImageDiv is called with delayDisplay=true
> but OpenLayers.Util.createImage is called with delayDisplay=false
> So no load observer for this image is created and it is forever
> img.style.display = "none"; 

Immediately after the line you changed, there is another set of load
listeners that are registered. So, I don't think this is quite the
problem you are looking for.

Can you investigate if the images are actually completing loading?
Firebug is useful for this.

> So my solution is:calling OpenLayers.Util.createImage with parameter
> delayDisplay.

I'd be really surprised if this solved the problem. The
image.style.display is only set to none (as far as I can see in Util) if 
delayDisplay is set to true -- so you shouldn't see the images hide at
all...

Regards,
-- 
Christopher Schmidt
MetaCarta