[OpenLayers-Users] IE6 performance

[Glen Stampoultzis]

On 13/11/2007, Christopher Schmidt <crschmidt at metacarta.com> wrote:
> On Mon, Nov 12, 2007 at 03:16:10PM +0000, Mapserver Lists wrote:
> > Dear All
> >
> > We are currently working on a project that integrates OL - using a
> > tilecache layer and a marker layer. We seem to be having some kind of
> > problem with IE6 however, as when it loads it seems to hang for a VERY
> > long time. I think that it seems to be loading all of the tiles and
> > markers first before rendering anything.
> >
> > Is this known behaviour or do we have our setup wrong. It works great
> > on FF and IE7.
>
> Without looking at your link, I'm guessing you're using the 'alpha'
> option on some transparent PNG layer to get transparency of images. This
> works on small images (the markers) to an extent, but IE6 doesn't have
> Alpha PNG support because the support that is available is too slow to
> use, so using the 'alpha' flag on a layer will likely cause exactly the
> behavior you just described. Since 'alpha' is only respected on IE6 (on
> other platforms it does nothing) this matches your description.
>
> Now I'll go look at your link. :)
>
> I was wrong. Instead, the problem is that you're loading > 1000 points
> into a map. This doesn't work for the same reason as above, though at
> least in this case, the project documentation is at fault. :)
>
> In theory, if you were to change the icon to being a .gif, you could
> make that transparent, and you'd get somewhat choppy edges, but it would
> work...
>
>   ... however, since the alpha-png hack is *always* applied, you'd have
> to do some hacking to turn that off. (Actually,
> OpenLayers.Util.alphaHack = function() { return false; } would
> accomplish that for you.)
>
> So, to test my theory, do:
>
> OpenLayers.Util.alphaHack = function() { return false; }
>
> If that works, then you can dig into the code and start trying to make
> it only do that on the markers (or make your control icons transparent
> pngs as well in some way).
>
> Sorry that this doesn't work more trivially yet, but I look forward to
> any info you can provide.
>

There's also a memory leak with markers in IE (for OL 2.4 not sure
about 2.5).  Even if you destroy them correctly.  For whatever reason
the memory leak tends to slow things down the longer than page is
open.

Either way 1000 markers on a page is not very feasible with IE.  From
our testing it's _way_ slower than most other browsers.