Review Request: Add support for building libplasma with GLES2

[Jammy Zhou]

> On Feb. 23, 2011, 5:29 p.m., Martin Gräßlin wrote:
> > The GLApplet seems to be unmaintained and is nowhere used in KDE (see http://lxr.kde.org/ident?i=GLApplet ). There was once one demo applet using it, but it has vanished.
> > 
> > GLApplet uses OpenGL only for glClear before passing the QPainter to the Plasmoid. I think we could just remove the background clearing and require it from the applet and drop the link to OpenGL completely.
> > 
> > Another thing is that given that it is just not used adding the complete GLES detection and building to Plasma does not make sense. It's probably better just to add a cmake option to disable building of the plasma applet (maybe using the mobile profile for that?).
> > 
> > The CMake stuff to find GLES is unfortunately not in a state to be included in kdelibs. I contacted build system some time ago and they gave me a nice list of things which need to be improved and it's still on my TODO stack :-(
> > 
> > It would be nice to have some input from Plasma devs here. Could you please add the Plasma group to the review?
> 
> Jammy Zhou wrote:
>     I'm a newbie for KDE development, what's GLApplet originally used for? And if GLApplet is really obsolete, maybe we'd better retire it to remove the dependency of libplasma on libGL. :)
>     
>     I also considered to remove glClear in GLApplet, but I'm not sure if it will cause some regressions, so I prepared this change.
>     
>     Anyway, waiting for inputs from plasma-devs to make final decision.
> 
> Martin Gräßlin wrote:
>     > what's GLApplet originally used for?
>     It allows to write a Plasmoid which can use OpenGL. Apparently there is no interest in doing so
>     > And if GLApplet is really obsolete, maybe we'd better retire it to remove the dependency of libplasma on libGL. :)
>     Yeah that would be nice. We cannot remove the class altogether, as that would break the ABI, but what should be done is deprecate it and add it to the list for removal in libplasma2. To get it free of OpenGL removing the glClear should be enough.
>     
>     > I also considered to remove glClear in GLApplet, but I'm not sure if it will cause some regressions, so I prepared this change.
>     As there is nothing using it at least in KDE repositories it probably won't cause regressions. Therefore I would give a +1 to remove it. Notmart or aseigo what do you think?
>     
>     Technical background for the non OpenGL devs in Plasma: the GLApplet has two lines of OpenGL code: it sets the clear color and clears the background. In normal speak, it repaints the background completely black. Afterwards the paint implementation of the applet is called which does the actual OpenGL rendering. Now the normal way in doing a paint process, is to first clear the background. If I would write an applet that's what I would have done in my code as I would not have expected the framework to clear already. It is also not documented that it does that and you do not always want to clear the background but want to continue to render on the previous frame.
>     
>     So the chances are that even if there exists an applet, which we do not know about, it would do the clearing itself.

Thanks for the detailed answers, Martin. I will prepare a new patch to remove the direct OpenGL dependency of libplasma as you suggested. I think if OpenGL rendering is really needed in libplasma, it can be done through QtOpenGL module, which can handle desktop OpenGL and OpenGL ES2.0 in Qt.


- Jammy


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On Feb. 24, 2011, 2:07 a.m., Jammy Zhou wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/100705/
> -----------------------------------------------------------
> 
> (Updated Feb. 24, 2011, 2:07 a.m.)
> 
> 
> Review request for kdelibs and Plasma.
> 
> 
> Summary
> -------
> 
> After build kwin with GLES2 code path, the kwin binary still has dependency on libGL.so, which is introduced by libplasma.so. Then we also need to add GLES2 support to libplasma, so that kwin/plasma only has dependency on libGLESv2.so in this case. 
> 
> The new option "BUILD_PLASMA_WITH_OPENGLES" added in attached patch is disabled by default, and distributions can turn it on when do packaging for OpenGL ES2.0 support.
> 
> 
> Diffs
> -----
> 
>   CMakeLists.txt 2dcc5ec 
>   cmake/modules/FindOpenGLES.cmake PRE-CREATION 
>   includes/CMakeLists.txt 9954c37 
>   plasma/CMakeLists.txt 8e6b0d7 
> 
> Diff: http://git.reviewboard.kde.org/r/100705/diff
> 
> 
> Testing
> -------
> 
> After turn the "BUILD_PLASMA_WITH_OPENGLES" option on, kwin-gles has no dependency on libGL.so now. And by default, libplasma still depends on libGL.so when run ldd.
> 
> 
> Thanks,
> 
> Jammy
> 
>

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