[Marble-devel] Re: Review Request: Multi-threaded texture mapping in Marble

Dennis Nienhüser earthwings at gentoo.org
Sat May 21 15:25:30 CEST 2011


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Ship it!


Tested it both on the Desktop and on the N900, seems to work nicely. Great work :-)

- Dennis


On May 17, 2011, 3:38 p.m., Bernhard Beschow wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/101378/
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> 
> (Updated May 17, 2011, 3:38 p.m.)
> 
> 
> Review request for Marble.
> 
> 
> Summary
> -------
> 
> This patch changes the scanline texture mappers to render textures with multiple threads.
> The number of threads is determined using QThread::idealThreadCount().
> The patch consists of two commits [1], where the first one refactors and cleans up the texture mappers, whereas the second one introduces the threading.
> 
> In the first commit, a class named ScanlineTextureMapperContext is introduced, which holds the state for performing scanline texture mapping. It was factored out of the AbstractScanlineTextureMapper class, which is now named "TextureMapperInterface". Fresh ScanlineTextureMapperContexts are created upon every rendering action, which is cleaner than the former approach of reinitializing all rendering attributes in AbstractScanlineTextureMapper::setRadius(). Finally, the patch constifies many variables in the texture mappers and removes some unneeded code.
> 
> In the second commit, threads are used for texture rendering. Almost all rendering logic has been moved into QRunnable implementations, which are recreated for every frame. Since each QRunnable instantiates its own ScanlineTextureMapperContext, the contexts are recreated for every frame as well.
> 
> Due to synchronization overhead for tile acces, the patch may cause a small performance regression. I couldn't measure any big difference on a single-core machine, though.
> 
> [1] https://github.com/shentok/marble/tree/threaded-rendering
> 
> 
> Diffs
> -----
> 
>   src/lib/AbstractScanlineTextureMapper.h 1998db0 
>   src/lib/AbstractScanlineTextureMapper.cpp 8acf57c 
>   src/lib/CMakeLists.txt f5d49c0 
>   src/lib/EquirectScanlineTextureMapper.h 05e6639 
>   src/lib/EquirectScanlineTextureMapper.cpp 8f697cc 
>   src/lib/MarbleMap.cpp 6f5f54f 
>   src/lib/MercatorScanlineTextureMapper.h a79d1c8 
>   src/lib/MercatorScanlineTextureMapper.cpp bdf9b0c 
>   src/lib/ScanlineTextureMapperContext.h PRE-CREATION 
>   src/lib/ScanlineTextureMapperContext.cpp PRE-CREATION 
>   src/lib/SphericalScanlineTextureMapper.h f336282 
>   src/lib/SphericalScanlineTextureMapper.cpp 583630a 
>   src/lib/StackedTileLoader.cpp b67cb98 
>   src/lib/TextureLayer.cpp d98f712 
>   src/lib/TextureMapperInterface.h PRE-CREATION 
>   src/lib/TextureMapperInterface.cpp PRE-CREATION 
>   src/lib/TileLoader.cpp 1b85dda 
>   src/lib/TileScalingTextureMapper.h 2c70dad 
>   src/lib/TileScalingTextureMapper.cpp 2ec719f 
>   src/lib/global.h a5c25fb 
> 
> Diff: http://git.reviewboard.kde.org/r/101378/diff
> 
> 
> Testing
> -------
> 
> Here are some numbers of a benchmark using OSM:
> 
> I get the following speedups on an Atom N270 (two Hyperthreads):
> o globe projection:
>   low quality:     ~29 -> ~32 fps
>   outline quality: ~20 -> ~25 fps
>   high quality:     ~5 ->  ~7 fps
> o flat projection:
>   low quality:     ~33 -> ~36 fps
>   outline quality: ~23 -> ~26 fps
>   high quality:     ~7 ->  ~9 fps
> o mercator projection:
>   low quality:     ~32 -> ~35 fps
>   outline quality: ~22 -> ~26 fps
>   high quality:     ~7 ->  ~9 fps
> 
> Earthwings gets the following speedups for globe projection on an Intel(R) Core(TM)2 Quad CPU Q8200 @ 2.33GHz (four "real" threads):
> low quality:     ~57 -> ~66 fps
> outline quality: ~37 -> ~48 fps
> high quality:    ~14 -> ~30 fps
> 
> I get about the same results before and after the patch is applied on a single-core machine.
> 
> 
> Thanks,
> 
> Bernhard
> 
>

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