1 Tips & FAQ 2 ========== 3 4 + [Gyp Options](#gypdefines) 5 + [Bitmap Subsetting](#bitmap-subsetting) 6 + [Capture a `.skp` file on a web page in Chromium](#skp-capture) 7 + [How to add hardware acceleration in Skia](#hw-acceleration) 8 + [Does Skia support Font hinting?](#font-hinting) 9 + [Does Skia shape text (kerning)?](#kerning) 10 11 * * * 12 13 <span id="gypdefines"></span> 14 15 Gyp Options 16 ----------- 17 18 When running `sync-and-gyp`, the `GYP_DEFINES` environment variable can 19 be used to change Skias compile-time settings, using a 20 space-separated list of key=value pairs. For example, to disable both 21 the Skia GPU backend and PDF backends, run it as follows: 22 23 <!--?prettify lang=sh?--> 24 25 GYP_DEFINES='skia_gpu=0 skia_pdf=0' python bin/sync-and-gyp 26 ninja -C out/Debug 27 28 Note: Setting enviroment variables in the Windows CMD.EXE shell [uses a 29 different syntax](/user/quick/windows#env). 30 31 You can also set environment variables such as `CC`, `CXX`, 32 `CFLAGS`, `CXXFLAGS`, or `CPPFLAGS` to control how Skia is compiled. 33 To build with clang, for example: 34 35 <!--?prettify lang=sh?--> 36 37 CC='clang' CXX='clang++' python bin/sync-and-gyp 38 ninja -C out/Debug 39 40 To build with clang and enable a compiler warning for unused parameters in C++ 41 (but not C or assembly) code: 42 43 <!--?prettify lang=sh?--> 44 45 CXXFLAGS='-Wunused-parameter' \ 46 CC='clang' CXX='clang++' python bin/sync-and-gyp 47 ninja -C out/Debug 48 49 50 The `GYP_GENERATORS` environment variable can be used to set the 51 build systems that you want to use (as a comma-separated list). 52 The default is `'ninja,msvs-ninja'` on Windows, `'ninja,xcode'` on 53 Mac OS X, and just `'ninja'` on Linux. For example, to generate 54 only Ninja files on Mac: 55 56 <!--?prettify lang=sh?--> 57 58 GYP_GENERATORS='ninja' python bin/sync-and-gyp 59 ninja -C out/Debug 60 61 Finally, the `SKIA_OUT` environment variable can be used to set 62 the path for the build directory. The default is `out` inside the 63 top-level Skia source directory. For example to test Skia with 64 two different compilers: 65 66 <!--?prettify lang=sh?--> 67 68 CC='clang' CXX='clang++' SKIA_OUT=~/build/skia_clang python bin/sync-and-gyp 69 CC='gcc' CXX='g++' SKIA_OUT=~/build/skia_gcc python bin/sync-and-gyp 70 ninja -C ~/build/skia_clang/Debug 71 ninja -C ~/build/skia_gcc/Debug 72 73 * * * 74 75 <span id="bitmap-subsetting"></span> 76 77 Bitmap Subsetting 78 ----------------- 79 80 Taking a subset of a bitmap is effectively free - no pixels are copied or 81 memory is allocated. This allows Skia to offer an API that typically operates 82 on entire bitmaps; clients who want to operate on a subset of a bitmap can use 83 the following pattern, here being used to magnify a portion of an image with 84 drawBitmapNine(): 85 86 SkBitmap subset; 87 bitmap.extractSubset(&subset, rect); 88 canvas->drawBitmapNine(subset, ...); 89 90 [An example](https://fiddle.skia.org/c/c91694020f0810994917b56c323e4559) 91 92 * * * 93 94 <span id="skp-capture"></span> 95 96 Capture a `.skp` file on a web page in Chromium 97 ----------------------------------------------- 98 99 1. Launch Chrome or Chromium with `--no-sandbox --enable-gpu-benchmarking` 100 2. Open the JS console (ctrl-shift-J) 101 3. Execute: `chrome.gpuBenchmarking.printToSkPicture('/tmp')` 102 This returns "undefined" on success. 103 104 Open the resulting file in the Skia Debugger, rasterize it with `dm`, 105 or use Skia's `SampleApp` to view it: 106 107 <!--?prettify lang=sh?--> 108 109 bin/sync-and-gyp 110 ninja -C out/Release debugger dm SampleApp 111 out/Release/debugger /tmp/layer_0.skp & 112 113 out/Release/dm --src skp --skps /tmp/layer_0.skp -w /tmp \ 114 --config 8888 gpu pdf --verbose 115 ls -l /tmp/*/skp/layer_0.skp.* 116 117 out/Release/SampleApp --picture /tmp/layer_0.skp 118 119 * * * 120 121 <span id="hw-acceleration"></span> 122 123 How to add hardware acceleration in Skia 124 ---------------------------------------- 125 126 There are two ways Skia takes advantage of specific hardware. 127 128 1. Subclass SkCanvas 129 130 Since all drawing calls go through SkCanvas, those calls can be 131 redirected to a different graphics API. SkGLCanvas has been 132 written to direct its drawing calls to OpenGL. See src/gl/ 133 134 2. Custom bottleneck routines 135 136 There are sets of bottleneck routines inside the blits of Skia 137 that can be replace on a platform in order to take advantage of 138 specific CPU features. One such example is the NEON SIMD 139 instructions on ARM v7 devices. See src/opts/ 140 141 * * * 142 143 <span id="font-hinting"></span> 144 145 Does Skia support Font hinting? 146 ------------------------------- 147 148 Skia has a built-in font cache, but it does not know how to actual render font 149 files like TrueType into its cache. For that it relies on the platform to 150 supply an instance of SkScalerContext. This is Skia's abstract interface for 151 communicating with a font scaler engine. In src/ports you can see support 152 files for FreeType, Mac OS X, and Windows GDI font engines. Other font 153 engines can easily be supported in a like manner. 154 155 156 * * * 157 158 <span id="kerning"></span> 159 160 Does Skia shape text (kerning)? 161 ------------------------------- 162 163 No. Skia provides interfaces to draw glyphs, but does not implement a 164 text shaper. Skia's client's often use 165 [HarfBuzz](http://www.freedesktop.org/wiki/Software/HarfBuzz/) to 166 generate the glyphs and their positions, including kerning. 167 168 <div style="margin-bottom:99%"></div> 169
