[Qgis-developer] SVG-Icons instead of PNGs?

John C. Tull jctull at gmail.com
Wed Aug 1 11:23:10 PDT 2012 

Hi Larry,

I took a look yesterday and was confused to find my interpretation of the scaling quality to be a little different than what you reported on OSX. With your update today, the pan select icon looks very good at various scales. I'm glad to see that the svg scaling is working good within qt and on OSX now.

Cheers,
John

On Aug 1, 2012, at 9:56 AM, Larry Shaffer <larrys at dakotacarto.com> wrote:

> Hi,
> 
> Well, after lots more testing and head-scratching, I came to realize
> the QSvgIconEngine plugin was not being bundled with the Mac builds.
> This was why SVG icons were being rendered but scaled like rasters.
> This skewed my previous SVG icon Qt scaling test. Sorry for that. I've
> included the plugin for Mac bundling [0].
> 
> This changes my previous results in two ways:
> 
> - I no longer see any issues with down- or up-scaling with any of the
> test SVG icons on Mac.
> - Robert's 24x24 SVG icons scale OK to 32x32. I have not tested the
> scaling up to 48x48. Since it is a straight 200% I expect it will
> render even better.
> 
> To test up-scaling, I have reverted mActionPanToSelected.svg back to
> Robert's original 24x24 design [1]. Set the icon preference to 32x32
> to test.
> 
> Since my testing on Mac was not up-scaling SVG icons before I did not
> notice the issue with the Default theme's switched-out SVGs with
> embedded rasters. They are now up-scaling very poorly to 32x32, where
> such embedded rasters were originally PNGs at 24x24
> (mActionPanToSelected and mActionRotateLabel).
> 
> Second Test Conclusions
> 
> - 48x48 base icon size would probably still be ideal as a single icon
> set base size, since it could be rasterized at that size (or lower) if
> PNGs are required for something. However, 24x24 base size may work
> well when scaled and rasterized (further tests needed here).
> 
> - Embedding rasters in SVGs (for having Default theme available while
> moving to an SVG-only theme) is not a good idea. The rasters up-scale
> poorly. I suggest a clean move to a SVG-only set, if QSvgIconEngine is
> to be leveraged to solve scaling problems for core icons. PNGs could
> still be supported once the getThemeIcon() method is removed, since it
> currently chooses the icon based upon file name and extension.
> 
> 
> [0] https://github.com/qgis/Quantum-GIS/commit/24eb02a99022e31b740f902204727cf1f25973ca
> [1] https://github.com/qgis/Quantum-GIS/commit/ba575794f8803c80f9defe59ba1a40020ebd2834
> 
> Regards,
> 
> Larry
> 
> 
> On Tue, Jul 31, 2012 at 3:49 PM, Larry Shaffer <larrys at dakotacarto.com> wrote:
>> On Tue, Jul 31, 2012 at 5:49 AM, Andreas Neumann <a.neumann at carto.net> wrote:
>>> I think it would be worth a try to use the SVG symbols directly - or at
>>> least offer the option to use them.
>> 
>> Hi Andreas, Giovanni, Robert and anyone else interested,
>> 
>> I have committed to master branch a preliminary test for SVG icon
>> scaling based upon Robert's icons. Ideally it should be tested on as
>> many platforms and devices as possible [0]. To test, please pull
>> latest master branch and compile, or wait for the nightly to come out.
>> 
>> 
>> Here's what I've done:
>> 
>> - Several PNG icons were switched out with SVG counterparts to test Qt
>> scaling on different platforms
>> - Added SVG icons to Default theme that are comprised of the regular
>> PNG embedded within
>> - Added SVG icons to GIS theme, mostly @ 32x32 and one @ 48x48 (note:
>> commit message is incorrect about 24x24)
>> - Testing with the supplied GIS theme allows for contrasting against
>> other similarly designed, preexisting PNG icons.
>> 
>> GIS theme Icons to test (with document, or page, size and description noted):
>> 
>> mActionPanToSelected.svg <- @32x32 (Pan Map to Selection tool)
>> mActionRotateLabel.svg <- @32x32 (Advanced labeling Rotate Label tool)
>> mActionSelectPolygon.svg <- @32x32 (Select Feature by Polygon tool)
>> mActionSplitFeatures.svg <- @48x48 (Split Feature tool)
>> 
>> 
>> To test:
>> 
>> 1) Set your icon theme to Default. View whether each test icon looks
>> as it did before. This will verify whether SVG with embedded PNGs of
>> the original icons works with your version of Qt. (QIcon notes Qt 4.2
>> or > icon engine supports SVG.) If we wanted to move to all SVG source
>> files right now, this would provide an intermediate step for existing
>> PNGs that don't have SVG counterparts.
>> 
>> 2) Switch to GIS theme and individually test the above noted icons at
>> the 16, 24, and 32 sizes.
>> 
>> - Test mActionPanToSelected by viewing in main menu, and as a toolbar button
>> - To test mActionRotateLabel, you will need a vector layer in edit
>> mode, and with data-defined rotation column. View toolbar button.
>> - Test mActionSelectPolygon by viewing it in the popup menu, main
>> menu, and as a toolbar button.
>> - To test mActionSplitFeatures, you will need a polygon vector layer
>> in edit mode, with two features selected. Also view in Edit menu
>> - Compare your results against mine [1]. Please share screen snaps of
>> any different findings.
>> 
>> 
>> My results on Mac, with Qt 4.8.1 and 4.8.2 [1]:
>> 
>> - Overall IMHO Qt down-scaling is better than that of PNG.
>> - SVG document size of 32x32 scaled to 24x24 (75%) showed some blurring.
>> - Qt will _not_ up-scale SVG toolbar buttons when setting the
>> toolbar's icon size, without doing so preprocessing first. SVG sources
>> used by the icon engine appear to be rasterized at their document
>> size, then later only scaled down when the icon size of the toolbar is
>> adjusted (just like PNGs). So, starting with an appropriate 'largest'
>> size for the SVG source seems to be key.
>> - Icons were pulled from OSGeo SVN repository and up-scaled in
>> Inkscape. SVG output from Illustrator CS5 could not be read.
>> 
>> 
>> Preliminary Conclusion
>> 
>> I think any single icon set, moving forward towards a 2.0 solution,
>> should be in the SVG format at 48x48 document size.
>> 
>> Marco B. has an issue ticket request for 48x48 size icons for use in
>> the QGIS mobile interface [2]. I think 48x48 document size scaled to
>> 16x16 or 24x24 looks good and sharp, with only slight blurring at
>> 32x32. So, 48x48 seems to work well for Qt scaling and addresses (at a
>> minimum) the mobile interface.
>> 
>> 
>> [0] https://github.com/qgis/Quantum-GIS/commit/738c1f36fe9bdcbeebce36014ff913dc091705fb
>> [1] http://dl.dropbox.com/u/4058089/qgis/svg-scaling-test.zip
>> [2] http://trac.osgeo.org/osgeo/ticket/846
>> 
>> 
>> Regards,
>> 
>> Larry
>> 
>> 
>>> Andreas
>>> 
>>> On Tue, 31 Jul 2012 12:38:07 +0200, G. Allegri wrote:
>>>> 
>>>> Scaling SVG in Inkscapes is known to be problematic. Are you sure that
>>>> this applies to Qt SVG scaling too?
>>>> 
>>>> giovanni
>>>> 
>>>> 2012/7/31 Robert Szczepanek
>>>> 
>>>>> Hi Andreas,
>>>>> 
>>>>> I made fast SVG downscaling test. Rendered with Inkscape.
>>>>> Second column is shifted vertically by 0,5px.
>>>>> As you can see main problem is "travelling blur" effect. Perhaps
>>>>> there are some smart renderers to overcome this.
>>>>> 
>>>>> I would also like to have just one SVG file...
>>>>> Robert
>>>>> 
>>>>> On 31.07.2012 10 [3]:30, Andreas Neumann wrote:
>>>>> 
>>>>>> Hi Robert,
>>>>>> 
>>>>>> Thanks for the reply.
>>>>>> 
>>>>>> Do you have a side-by-side comparison of SVG vs. png and the
>>>>>> rendering
>>>>>> quality somewhere? I wonder if this is still an issue and if it
>>>>>> is - how
>>>>>> much of a problem it really is.
>>>>>> 
>>>>>> Having just one icon size instead of n different sizes also has a
>>>>>> lot of
>>>>>> advantages. Think about all the new high-dpi devices. These would
>>>>>> benefit a lot from SVG instead of PNG.
>>>>>> 
>>>>>> Andreas
>>>>>> 
>>>>>> On Tue, 31 Jul 2012 00:53:40 +0200, Robert Szczepanek wrote:
>>>>>> 
>>>>>>> Hi Andreas,
>>>>>>> 
>>>>>>> On 29.07.2012 12:22, Andreas Neumann wrote:
>>>>>>> 
>>>>>>>> Regarding the discussion around the icons?
>>>>>>>> 
>>>>>>>> How about using SVG icons instead of fixed size png icons?
>>>>>>>> That way one
>>>>>>>> could easily scale the icon sizes on different devices to the
>>>>>>>> preferred
>>>>>>>> scale and taste of the user.
>>>>>>> 
>>>>>>> 
>>>>>>> From my test and literature I found that simple vector scaling
>>>>>>> for
>>>>>>> small size icons (16x16 - 24-24) is not recommended. For higher
>>>>>>> images
>>>>>>> blur effect is not so visible and important.
>>>>>>> 
>>>>>>>> Are there any technical reasons for using PNGs instead of
>>>>>>>> SVGs? I
>>>>>>>> believe the source of the icons is SVG anyway?
>>>>>>>> 
>>>>>>>> For my own in house python plugins I always use the SVG
>>>>>>>> icons.
>>>>>>> 
>>>>>>> 
>>>>>>> The main technical reason was image quality. We decided to use
>>>>>>> already rendered images in "native resolution". I know it
>>>>>>> sounds
>>>>>>> stupid in Scalable Vector ... context, but that's the reality.
>>>>>>> Whole version 0.1 of GIS icons was designed in just one SVG
>>>>>>> file. In
>>>>>>> version 0.2 I save them in separate files. So most of the icons
>>>>>>> is at
>>>>>>> the moment available as one file per icon.
>>>>>>> 
>>>>>>> regards,
>>>>>>> Robert
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> Qgis-developer mailing list
>>>>> Qgis-developer at lists.osgeo.org [4]
>>>>> http://lists.osgeo.org/mailman/listinfo/qgis-developer [5]
>>>> 
>>>> 
>>>> 
>>>> 
>>>> Links:
>>>> ------
>>>> [1] mailto:Qgis-developer at lists.osgeo.org
>>>> [2] http://lists.osgeo.org/mailman/listinfo/qgis-developer
>>>> [3] http://webmail.carto.net/tel:31.07.2012%2010
>>>> [4] mailto:Qgis-developer at lists.osgeo.org
>>>> [5] http://lists.osgeo.org/mailman/listinfo/qgis-developer
>>>> [6] mailto:robert at szczepanek.pl
>>> 
>>> 
>>> --
>>> --
>>> Andreas Neumann
>>> Böschacherstrasse 10A
>>> 8624 Grüt (Gossau ZH)
>>> Switzerland
>>> _______________________________________________
>>> Qgis-developer mailing list
>>> Qgis-developer at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/qgis-developer
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