[OpenLayers-Dev] WMS: jpeg override

[Christopher Schmidt]

On Thu, Mar 12, 2009 at 09:43:27AM +0100, bartvde at osgis.nl wrote:
> Okay, let me give an example why this bothers me.
> 
> When reading in a WMC document with layerParams:
> 
> var format = new OpenLayers.Format.WMC({layerParams: {transparent:
> 'TRUE'}, layerOptions: {isBaseLayer: false, singleTile: true, buffer: 0,
> ratio: 1, displayOutsideMaxExtent: true}});
> 
> I want all WMS overlays to be transparent. But there can be 1 layer at the
> bottom of the stack which is a jpeg aerial photograph in the WMC.

If you know this, why can't you just 'del layers[0].params.transparent'
from the results of the WMC? 

The reason that the automatic changing is in there is that for a while,
the most common question received on the OL list was "Why can't I see
through my  overlays!?" The fact that jpg is the default format means
that many people had no idea they were using jpegs at all, and so they
had no idea why they just got black imagery.

I would say that your use case is a corner case; not the common one.
I would be willing to have a non-default layer option like 'noMagic'
which turns off the magical work that is done here, since I agree it can
be a problem in rare cases, but by default, it helps us avoid a lot of
questions.

THanks for the use case. It does help focus the discussions.

> So I would need some kind of conditional layerParams, which is currently
> not possible and a bit of a hassle to implement.
> 
> That's why I am advocating removing the jpeg override.



> Best regards,
> Bart
> 
> > Hi list,
> >
> > currently when using a WMS layer as jpeg and transparent true, OL
> > "automagically" override the image format to png or gif. This has caused
> > me quite a few headaches in the past weeks to be honest.
> >
> > I would rather have that transparent true is just ignored, and that the
> > image format remains jpeg. In the end, this is what a WMS does when it
> > receives &format=image/jpeg&transparent=TRUE. So why not leave this up to
> > the WMS to deal with it, and maybe write a warning message to the console
> > for the app developer in debug mode?
> >
> > Btw, I am talking about this piece of code:
> >
> >             // jpegs can never be transparent, so intelligently switch the
> >             //  format, depending on teh browser's capabilities
> >             if (this.params.FORMAT == "image/jpeg") {
> >                 this.params.FORMAT = OpenLayers.Util.alphaHack() ?
> > "image/gif"
> >                                                                  :
> > "image/png";
> >             }
> >
> > What do others think?
> >
> > Best regards,
> > Bart
> >
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> >
> 
> 
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-- 
Christopher Schmidt
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