1Skia Viewer
2==========================
3The Skia Viewer displays a series of slides that exhibit specific features of Skia, including the Skia GMs and programmed samples that allow interaction. In addition, the Viewer is used to debug and understand different parts of the Skia system:
4
5* Observe rendering performance - placing the Viewer in stats mode displays average frame times.
6* Try different rendering methods - it's possible to cycle among the three rendering methods: raster, OpenGL and Vulkan (on supported platforms). You can use this with stats mode to see the effect that the different rendering methods have on drawing performance.
7* Display and manipulate your own pictures.
8
9Some slides require resources stored outside the program. These resources are stored in the `<skia-path>/resources` directory.
10
11Linux, Macintosh and Windows
12----------------------------
13
14The Viewer can be built using the regular GN build process, e.g.
15
16    bin/gn gen out/Release --args='is_debug=false'
17    ninja -C out/Release viewer
18
19To load resources in the desktop Viewers, use the `--resourcePath` option:
20
21    <skia-path>/out/Release/viewer --resourcePath <skia-path>/resources
22
23Similarly, `--skps <skp-file-path>` will load any `.skp` files in that directory
24for display within the Viewer.
25
26Other useful command-line options: using `--match <pattern>` will load only SKPs or slides
27matching that name; using `--slide <name>` will launch at that slide; and you can start up
28with a particular rendering method by using `--backend`, i.e., `--backend sw`, `--backend gl`,
29`--backend vk`, or `--backend mtl`.
30
31The desktop Viewers are controlled using the keyboard and mouse: left (←) and right
32(→) arrows to move from slide to slide; up (↑) and down (↓) arrows to
33zoom in and out; clicking and dragging will translate. Other display options and a slide
34picker can be found in the Tools UI, which can be toggled by hitting the spacebar.
35
36Key    | Action
37-------|-------------
38← →    | Move between the slides
39↑ ↓    | Zoom in / out
40d      | Change render methods among raster, OpenGL and Vulkan
41s      | Display rendering times and graph
42Space  | Toggle display of Tools UI
43
44Android
45-------
46
47To build Viewer as an Android App, first follow the
48[Android build instructions](https://skia.org/user/build#android) to set up the
49Android NDK and a ninja out directory. In addition, you will need the
50[Android SDK](https://developer.android.com/studio/#command-tools) installed and your
51`ANDROID_HOME` environment variable set.
52
53    mkdir ~/android-sdk
54    ( cd ~/android-sdk; unzip ~/Downloads/sdk-tools-*.zip )
55    yes | ~/android-sdk/tools/bin/sdkmanager --licenses
56    export ANDROID_HOME=~/android-sdk  # Or wherever you installed the Android SDK.
57
58If you are not using the NDK included with the Android SDK (at ~/android-sdk/ndk-bundle
59in this example) you'll need to set the environmental variable `ANDROID_NDK_HOME`, e.g.,
60
61    export ANDROID_NDK_HOME=/tmp/ndk
62
63The Viewer APK must be built by gradle which can be invoked on the command line
64with the following script:
65
66    platform_tools/android/bin/android_build_app -C <out_dir> viewer
67
68where `<out_dir>` is the ninja out directory (e.g., `out/arm64`)
69that you created. Upon completion of the script the APK
70can be found at `<out_dir>/viewer.apk`
71
72To load resources in the Android Viewer place them in
73`/data/local/tmp/resources`; to load SKPs place them in `/data/local/tmp/skps`.
74
75Swiping left and right will switch slides, pinch-zoom will zoom in and out, and
76display options are available in the UI.
77
78iOS
79---
80
81Viewer on iOS is built using the regular GN process, e.g.
82
83    bin/gn gen out/Release --args='target_os="ios" is_debug=false'
84    ninja -C out/Release viewer
85
86Like other iOS apps it can be deployed either by using something like
87[ios-deploy](https://github.com/ios-control/ios-deploy)
88or by building within Xcode and launching via the IDE. See the
89[iOS build instructions](https://skia.org/user/build#ios) for more information
90on managing provisioning profiles for signing and deployment.
91
92Viewer will
93automatically bundle the `resources` directory in the top-level Skia directory,
94and will bundle an `skps` directory if also placed in the Skia directory.
95
96On iOS the Viewer provides basic touch functionality: you can view slides,
97swipe between them, pinch-zoom to scale, and translate via panning. There is not
98yet support for display options or selecting from a list of slides.
99