7c1dc52783
This is simply being lazy and requiring the mutex held for all Skia operations. With the effort to verify things it'd presumably be possible to make the code thread-safe. Change-Id: I748dbf2d5af66dcd140b5a9d6d57e9d848babf0e Reviewed-on: https://gerrit.libreoffice.org/c/core/+/103564 Tested-by: Jenkins Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
85 lines
3.4 KiB
Text
85 lines
3.4 KiB
Text
This is code for using the Skia library as a drawing library in VCL backends.
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See external/skia for info on the library itself.
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Environment variables:
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======================
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See README.vars in the toplevel vcl/ directory. Note that many backends do not
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use Skia. E.g. on Linux it is necessary to also use SAL_USE_VCLPLUGIN=gen .
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There are also GUI options for controlling whether Skia is enabled.
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Skia drawing methods:
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=====================
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Skia supports several methods to draw:
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- Raster - CPU-based drawing (here primarily used for debugging)
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- Vulkan - Vulkan-based GPU drawing, this is the default
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There are more (OpenGL, Metal on Mac, etc.), but (as of now) they are not supported by VCL.
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Logging:
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========
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Run LO with 'SAL_LOG=+INFO.vcl.skia' to get log information about Skia including
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tracing each drawing operation. If you want log information without drawing operations,
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use 'SAL_LOG=+INFO.vcl.skia-INFO.vcl.skia.trace'.
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Debugging:
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==========
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Both SkiaSalBitmap and SkiaSalGraphicsImpl have a dump() method that writes a PNG
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with the current contents. There is also SkiaHelper::dump() for dumping contents
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of SkBitmap, SkImage and SkSurface.
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If there is a drawing problem, you can use something like the following piece of code
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to dump an image after each relevant operation (or do it in postDraw() if you don't
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know which operation is responsible). You can then find the relevant image
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and match it with the responsible operation (run LO with 'SAL_LOG=+INFO.vcl.skia').
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static int cnt = 0;
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++cnt;
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char buf[100];
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sprintf(buf,"/tmp/a%05d.png", cnt);
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SAL_DEBUG("CNT:" << cnt);
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if(cnt > 4000) // skip some initial drawing operations
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dump(buf);
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Testing:
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========
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Currently unittests always use the 'headless' VCL backend. Use something like the following
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to run VCL unittests with Skia (and possibly skip slowcheck):
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SAL_SKIA=raster SAL_ENABLESKIA=1 SAL_USE_VCLPLUGIN=gen make vcl.build vcl.unitcheck vcl.slowcheck
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You can also use 'visualbackendtest' to visually check some operations. Use something like:
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SAL_SKIA=raster SAL_ENABLESKIA=1 SAL_USE_VCLPLUGIN=gen [srcdir]/bin/run visualbackendtest
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Thread safety:
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==============
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SolarMutex must be held for most operations (asserted in SkiaSalGraphicsImpl::preDraw() and
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in SkiaZone constructor). The reason for this is that this restriction does not appear to be
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a problem, so there's no need to verify thread safety of the code (including the Skia library).
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There's probably no fundamental reason why the code couldn't be made thread-safe.
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GrDirectContext sharing:
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========================
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We use Skia's sk_app::WindowContext class for creating surfaces for windows, that class
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takes care of the internals. But of offscreen drawing, we need an instance of class
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GrDirectContext. There is sk_app::WindowContext::getGrDirectContext(), but each instance creates
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its own GrDirectContext, and apparently it does not work to mix them. Which means that
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for offscreen drawing we would need to know which window (and only that window)
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the contents will be eventually painted to, which is not possible (it may not even
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be known at the time).
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To solve this problem we patch sk_app::WindowContext to create just one GrDirectContext object
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and share it between instances. Additionally, using sk_app::WindowContext::SharedGrDirectContext
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it is possible to share it also for offscreen drawing, including keeping proper reference
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count.
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