b5002394d1
* /user/download: remove instruction to compile and run skia
tests - moved to /user/quick/${OS}
* /user/quick/desktop: move Gyp options to a section in the
FAQ (distracts from quick start narritive).
* /user/tips: reformat, rewrite.
NOTRY=true
DOCS_PREVIEW= https://skia.org/?cl=1443653002
Review URL: https://codereview.chromium.org/1443653002
135 lines
4.1 KiB
Markdown
135 lines
4.1 KiB
Markdown
Tips & FAQ
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==========
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<span id="gypdefines"></span>
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Gyp Options
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-----------
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When running `sync-and-gyp`, the `GYP_DEFINES` environment variable can
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be used to change Skia’s compile-time settings, using a
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space-separated list of key=value pairs. For example, to disable both
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the Skia GPU backend and PDF backends, run it as follows:
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<!--?prettify lang=sh?-->
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GYP_DEFINES='skia_gpu=0 skia_pdf=0' python bin/sync-and-gyp
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ninja -C out/Debug
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Note: Setting enviroment variables in the Windows CMD.EXE shell [uses a
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different syntax](/user/quick/windows#env).
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You can also set environment variables such as `CC`, `CXX`,
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`CFLAGS`, or `CPPFLAGS` to control how Skia is compiled. For
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example:
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<!--?prettify lang=sh?-->
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CC='clang' CXX='clang++' python bin/sync-and-gyp
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ninja -C out/Debug
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The `GYP_GENERATORS` environment variable can be used to set the
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build systems that you want to use (as a comma-separated list).
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The default is `'ninja,msvs-ninja'` on Windows, `'ninja,xcode'` on
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Mac OS X, and just `'ninja'` on Linux. For example, to generate
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only Ninja files on Mac:
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<!--?prettify lang=sh?-->
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GYP_GENERATORS='ninja' python bin/sync-and-gyp
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ninja -C out/Debug
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Finally, the `SKIA_OUT` environment variable can be used to set
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the path for the build directory. The default is `out` inside the
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top-level Skia source directory. For example to test Skia with
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two different compilers:
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<!--?prettify lang=sh?-->
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CC='clang' CXX='clang++' SKIA_OUT=~/build/skia_clang python bin/sync-and-gyp
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CC='gcc' CXX='g++' SKIA_OUT=~/build/skia_gcc python bin/sync-and-gyp
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ninja -C ~/build/skia_clang/Debug
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ninja -C ~/build/skia_gcc/Debug
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* * *
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<span id="bitmap-subsetting"></span>
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Bitmap Subsetting
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-----------------
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Taking a subset of a bitmap is effectively free - no pixels are copied or
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memory is allocated. This allows Skia to offer an API that typically operates
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on entire bitmaps; clients who want to operate on a subset of a bitmap can use
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the following pattern, here being used to magnify a portion of an image with
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drawBitmapNine():
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SkBitmap subset;
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bitmap.extractSubset(&subset, rect);
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canvas->drawBitmapNine(subset, ...);
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* * *
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<span id="skp-capture"></span>
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Capture a `.skp` file on a web page in Chromium
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-----------------------------------------------
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1. Launch Chrome or Chromium with `--no-sandbox --enable-gpu-benchmarking`
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2. Open the JS console (ctrl-shift-J)
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3. Execute: `chrome.gpuBenchmarking.printToSkPicture('/tmp')`
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This returns "undefined" on success.
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Open the resulting file in the Skia Debugger, rasterize it with `dm`,
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or use Skia's `SampleApp` to view it:
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<!--?prettify lang=sh?-->
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bin/sync-and-gyp
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ninja -C out/Release debugger dm SampleApp
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out/Release/debugger /tmp/layer_0.skp &
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out/Release/dm --src skp --skps /tmp/layer_0.skp -w /tmp \
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--config 8888 gpu pdf --verbose
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ls -l /tmp/*/skp/layer_0.skp.*
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out/Release/SampleApp --picture /tmp/layer_0.skp
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* * *
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<span id="hw-acceleration"></span>
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How to add hardware acceleration in Skia
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----------------------------------------
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There are two ways Skia takes advantage of specific hardware.
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1. Subclass SkCanvas
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Since all drawing calls go through SkCanvas, those calls can be
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redirected to a different graphics API. SkGLCanvas has been
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written to direct its drawing calls to OpenGL. See src/gl/
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2. Custom bottleneck routines
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There are sets of bottleneck routines inside the blits of Skia
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that can be replace on a platform in order to take advantage of
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specific CPU features. One such example is the NEON SIMD
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instructions on ARM v7 devices. See src/opts/
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* * *
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<span id="font-hinting"></span>
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Does Skia support Font hinting?
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-------------------------------
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Skia has a built-in font cache, but it does not know how to actual render font
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files like TrueType? into its cache. For that it relies on the platform to
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supply an instance of SkScalerContext?. This is Skia's abstract interface for
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communicating with a font scaler engine. In src/ports you can see support
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files for FreeType?, Mac OS X, and Windows GDI font engines. Other font
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engines can easily be supported in a like manner.
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