Transparent WMS Layer aren't shown transparent.

[qgib]

Author Name: Redmine Admin (Redmine Admin)
Original Redmine Issue: 179

Redmine category:web_services_clients/wms
Assignee: Gary Sherman

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I believe, that since my update from QT-4.1.2 to QT-4.1.3 former transparent shown WMS layer are shown opaque now. Perhaps is hasn't any relation to my QT update. For test you can try the following small swiss WMS service:

http://www.sogis1.so.ch/cgi-bin/sogis/sogis_uep.wms

Please regard it's a large scale layer and it should appear transparent.

[qgib]

Author Name: Gavin Macaulay - (Gavin Macaulay -)

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Browsing the Trolltech task tracker yields two bugs that may be causing this problem:

http://www.trolltech.com/developer/task-tracker/index_html?method=entry&id=116149

http://www.trolltech.com/developer/task-tracker/index_html?method=entry&id=119696

Both are scheduled to be fixed in the 4.2.0 version of Qt

[qgib]

Author Name: Brendan Morley - (Brendan Morley -)

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I tried your http://www.sogis1.so.ch/cgi-bin/sogis/sogis_uep.wms WMS URL today;

It comes up with one layer (Übersichtsplan) which then appears to be completely blank. e.g. the Full layer extent at http://www.sogis1.so.ch/cgi-bin/sogis/sogis_uep.wms?SERVICE=WMS&VERSION=1.1.0&REQUEST=GetMap&BBOX=7.340840,47.074200,8.033780,47.504100&SRS=EPSG:4326&WIDTH=578&HEIGHT=359&LAYERS=uep&STYLES=&FORMAT=image/png&TRANSPARENT=TRUE

Transparent layers work in QGIS (e.g. qgis-0.8.0-win32-060724) so I'm going to close this ticket until such time that someone else can reproduce it.

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• status_id was changed from Open to Closed
• resolution was changed from to worksforme

[qgib]

Author Name: Redmine Admin (Redmine Admin)

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With qgis-0-8.0-win32-060724 it works for me. But my [[RedHat]] QGIS does not work. If you like to see the spatial Data you have to set the following BBOX: 7.65519,47.17545,7.66674,47.18626

You will see the opaque effect when you add a second WMS layer with mentioned BBOX
Try http://www.sogis1.so.ch/cgi-bin/sogis/sogis_ch?
select the layer gemeinde_01 (Gemeindegrenzen Solothurn). The first layer of the TOC will cover the second layer.

My QT-version 4.1.3.

I hope this will explain much more better the mentioned behavior.

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• status_id was changed from Closed to Feedback
• resolution was changed from worksforme to

[qgib]

Author Name: Brendan Morley - (Brendan Morley -)

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I suppose the same opaque effect could be had for you when the background colour is set to non-white (through the Settings > Project Properties > General > Map Appearance settings) and you use the "http://www.sogis1.so.ch/cgi-bin/sogis/sogis_ch?" / "gemeinde_01" layer combination?

I have FC4 and Qt 4.1.0 and the above combo lets my non-white background show through (i.e. no bug). So I'm finding it difficult to reproduce. Perhaps we can put something in the release notes? Can you try with Qt4.1.0 at all?

[qgib]

Author Name: Redmine Admin (Redmine Admin)

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No it is not possible to try it with QT4.1.0 due to some bugs of QT which will have influence to the stability of QGIS. I changed from QT4.1.2 where transparent WMS works to QT4.1.3 where transparent WMS doesn't work. The need of update QT to 4.1.3 was based on some Gnome gdm incompatibilities which leeds to QGIS crashes. Can you try it with QT4.1.3??

[qgib]

Author Name: Redmine Admin (Redmine Admin)

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OK I changed from QT4.1.3 to QT4.1.0 and the transparency works without rebuild QGIS!! It looks like QT4.1.3 is the culprit.

When I connect to my WMS Layer the terminal throws tons of the following warnings:

Warning: Object::connect: No such signal [[QgsRasterLayer]]::drawingProgress(int,int)
Warning: QPaintEngine::setSystemRect, should not be changed while engine is active
Warning: QPaintEngine::setSystemClip(), should not be changed while engine is active

.... tons of these 2 lines ...

Warning: QPaintEngine::setSystemRect, should not be changed while engine is active
Warning: QPaintEngine::setSystemClip(), should not be changed while engine is active
Warning: Object::disconnect: No such signal [[QgsRasterLayer]]::drawingProgress(int,int)

Perhaps this can help you and me.

[qgib]

Author Name: Brendan Morley - (Brendan Morley -)

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Is it 4.1.0 that throws up all those warnings or 4.1.3?

I think the resolution to this is to add a release note to avoid 4.1.3 with transparent WMS layers. Your opinion?

[qgib]

Author Name: Redmine Admin (Redmine Admin)

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Ups... Of course it's my mistake. 4.1.3 throws the messages.

Your suggested solution sounds like ESRI Support. Long time ago I had a problem with a non working [[ArcView]]3 feature. The ESRI Solution was to fix the documentation in regard to the error and not the faulty feature.

All jokes aside, but 4.1.4 doesn't work too.

[qgib]

Author Name: Gavin Macaulay - (Gavin Macaulay -)

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We're in a bit of a sticky situation here. Versions of Qt prior to 4.1.4 have other problems that have caused bugs in Qgis.

This particular problem is quite likely to be caused by one of the two bugs on Qt's tracker (see the first comment in this ticket). One of these has been flagged as fixed, and will be available in the next release of Qt. The other bug was put down to programmer error - perhaps we could look at how Qgis does things with the comments in that bug in mind.

[qgib]

Author Name: Redmine Admin (Redmine Admin)

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I'm in doubt about the relation between the two QT bugs and our problem. 1. They were discovered at version 4.1.2, this version works fine for me. 2. The tickets do refer to PNG images. But GIF images are also shown opaque.

Unfortunately I'm not a great QT/C++ programmer, so I can't support you in this way.

I agree to your statement that versions of Qt prior to 4.1.4 have other problems that have caused bugs in Qgis.

It would be great when we are able to present transparent WMS layer at the FOSS4G2006 in Lausanne.

[qgib]

Author Name: Brendan Morley - (Brendan Morley -)

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Over the next few days I'll grab the latest Qt (4.1.4) and see if I can reproduce the error. This may be a low-priority activity for me though.

[qgib]

Author Name: Brendan Morley - (Brendan Morley -)

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I'm having issues getting 4.1.4 but in the meantime this may be another Qt bug that simulates this problem: http://www.trolltech.com/developer/task-tracker/index_html?method=entry&id=118082

[qgib]

Author Name: Brendan Morley - (Brendan Morley -)

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I finally was able to test this against Qt 4.1.3.

I am now also getting the following errors while retrieving the WMS layer:

Warning: QPaintEngine::setSystemRect, should not be changed while engine is active
Warning: QPaintEngine::setSystemClip(), should not be changed while engine is active

And the byte count is no longer updating.

HOWEVER, the http://www.sogis1.so.ch/cgi-bin/sogis/sogis_ch? server / gemeinde_01 layer / PNG encoding still gives a transparent background. I otherwise have a FC4 system.

I'm fast running out of ways of reproducing the problem, so I might leave this ticket dormant. I will have to raise another ticket to address the paint engine issue.

[qgib]

Author Name: Gavin Macaulay - (Gavin Macaulay -)

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Note that the QPaintEngine() warnings are due to an aspect of how qgis is trying to use the Qt4 canvas stuff. This problem has also been reported in ticket #10198, albeit with different symptons.

[qgib]

Author Name: Brendan Morley - (Brendan Morley -)

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I'm going to push this out from a 0.8 release as it doesn't appear to be a problem with QGIS and therefore shouldn't block its release. It's possibly not even a problem with Qt, perhaps being a problem with whatever libpng is being used to render the image.

I'm going to bow out of this one and let someone else have a go at it.

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• status_id was changed from Feedback to Open

[qgib]

Author Name: Redmine Admin (Redmine Admin)

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I cant' reproduce this with Kubuntu Feisty 7.04, QGIS 0.8.1p3 built against Qt 4.2.3. Is it still problem or could be closed now?

[qgib]

Author Name: horst-duester - (horst-duester -)

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The problem seems to be solved with QT4.2.x. I believe it can be closed now.

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• resolution was changed from to fixed
• status_id was changed from Open to Closed

[qgib]

Author Name: Anónimo (Anónimo)

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Milestone Version 0.9 deleted