Adding user doc section and core files for new site

site/user/sample/building.md

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+Building with Skia Tutorial
+===========================
+
+dsinclair@chromium.org
+
+
+This document describes the steps used to create an application that uses Skia.  The assumptions are that you're using:
+
+  * [git](http://git-scm.com)
+  * [gclient](https://code.google.com/p/gclient/)
+  * [gyp](https://code.google.com/p/gyp/)
+  * [ninja](http://martine.github.io/ninja/)
+
+I'm going to describe up to the point where we can build a simple application that prints out an SkPaint.
+
+Overview
+--------
+
+  1. Create remote repository.
+  1. Configure and sync using gclient.
+  1. Create DEPS file to pull in third party repositories.
+  1. Setup gitignore for directories pulled in from DEPS.
+  1. Configure GYP.
+  1. Setup GYP auto-run when gclient sync is executed.
+
+gclient setup
+-------------
+The first step is to setup a remote git repo, take your pick of provider. In
+my case, the repo is called UsingSkia and lives on
+[bitbucket](https://bitbucket.org).
+
+With the remote repo created, we create a .gclient configuration file. The
+gclient config command will write the file for us:
+
+    $ gclient config --name=src https://bitbucket.org/dj2/usingskia.git
+
+This will create the following:
+
+    solutions = [
+      { "name"        : "src",
+        "url"         : "https://bitbucket.org/dj2/usingskia.git",
+        "deps_file"   : "DEPS",
+        "managed"     : True,
+        "custom_deps" : {
+        },
+        "safesync_url": "",
+      },
+    ]
+    cache_dir = None
+
+The name that we configured is the directory in which the repo will be checked
+out. This is done by running gclient sync. There is a bit of magic that
+gclient does around the url to determine if the repo is SVN or GIT. I've found
+the use of ssh:// and the .git on the end seem to work to get the right SCM
+type.
+
+    $ gclient sync
+
+This should execute a bunch of commands (and, in this case, may end with an
+error because the repo was empty. That seems to be fine.) When finished, you
+should have a src directory with your git repository checked out.
+
+DEPS
+----
+
+With the repo created we can go ahead and create our src/DEPS file. The DEPS
+file is used by gclient to checkout the dependent repositories of our
+application. In this case, the Skia repository.
+
+Create a src/DEPS file with the following:
+
+~~~~
+
+  vars = {
+    "skia_revision": "a6a8f00a3977e71dbce9da50a32c5e9a51c49285",
+  }
+
+  deps = {
+    "src/third_party/skia/":
+        "http://skia.googlecode.com/skia.git@" + Var("skia_revision"),
+  }
+
+~~~~
+
+There are two sections to the `DEPS` file at the moment, `vars` and `deps`.
+The `vars` sections defines variables we can use later in the file with the
+`Var()` accessor. In this case, we define our root directory, a shorter name
+for any googlecode repositories and a specific revision of Skia that we're
+going to use. I've pinned to a specific version to insulate the application
+from changes in the Skia tree. This lets us know that when someone checks out
+the repo they'll be using the same version of Skia that we've built and tested
+against.
+
+The `deps` section defines our dependencies. Currently we have one dependency
+which we're going to checkout into the `src/third_party/skia` directory.
+
+Once the deps file is created, commit and push it to the remote repository.
+Once done, we can use gclient to checkout our dependencies.
+
+    $ gclient sync
+
+This should output a whole bunch of lines about files that are being added to
+your project. This may also be a good time to create a `.gitignore` file. You
+don't want to check the `third_party/skia directory` into your repository as
+it's being managed by gclient.
+
+Now, we've run into a problem. Skia itself has a `DEPS` file which defines the
+`third_party` libraries it needs to build. None of those dependencies are being
+checked out so Skia will fail to build.
+
+The way I found around that is to add a second solution to the `.gclient`
+file.  This solution tells gclient about Skia and will pull in the needed
+dependencies. I edited my `.gclient` file (created by the `gclient config`
+command above) to look as follows:
+
+    solutions = [
+      { "name"        : "src",
+        "url"         : "https://bitbucket.org/dj2/usingskia.git",
+        "deps_file"   : "DEPS",
+        "managed"     : True,
+        "custom_deps" : {
+        },
+        "safesync_url": "",
+      },
+      { "name"        : "src/third_party/skia",
+        "url"         : "http://skia.googlecode.com/skia.git@a6a8f00a3977e71dbce9da50a32c5e9a51c49285",
+        "deps_file"   : "DEPS",
+        "managed"     : True,
+        "custom_deps" : {
+        },
+        "safesync_url": "",
+      },
+    ]
+    cache_dir = None
+
+This is a little annoying at the moment since I've duplicated the repository
+revision number in the `.gclient` file. I'm hoping to find a way to do this
+through the `DEPS` file, but until then, this seems to work.
+
+With that done, re-run `gclient sync` and you should see a whole lot more
+repositories being checked out. The
+`src/third_party/skia/third_party/externals` directory should now be
+populated.
+
+GYP
+---
+
+The final piece of infrastructure we need to set up is GYP. GYP is a build
+system generator, in this project we're going to have it build ninja
+configuration files.
+
+First, we need to add GYP to our project. We'll do that by adding a new entry
+to the deps section of the `DEPS` file.
+
+    "src/tools/gyp":
+        (Var("googlecode_url") % "gyp") + "/trunk@1700",
+
+As you can see, I'm going to put the library into `src/tools/gyp` and checkout
+revision 1700 (note, the revision used here, 1700, was the head revision at
+the time the `DEPS` file was written. You're probably safe to use the
+tip-of-tree revision in your `DEPS` file).  A quick `gclient sync` and we
+should have everything checked out.
+ 
+In order to run GYP we'll create a wrapper script. I've called this
+`src/build/gyp_using_skia`.
+
+~~~~
+#!/usr/bin/python
+import os
+import sys
+
+script_dir = os.path.dirname(__file__)
+using_skia_src = os.path.abspath(os.path.join(script_dir, os.pardir))
+
+sys.path.insert(0, os.path.join(using_skia_src, 'tools', 'gyp', 'pylib'))
+import gyp
+
+if __name__ == '__main__':
+  args = sys.argv[1:]
+
+  if not os.environ.get('GYP_GENERATORS'):
+    os.environ['GYP_GENERATORS'] = 'ninja'
+
+  args.append('--check')
+  args.append('-I%s/third_party/skia/gyp/common.gypi' % using_skia_src)
+
+  args.append(os.path.join(script_dir, '..', 'using_skia.gyp'))
+
+  print 'Updating projects from gyp files...'
+  sys.stdout.flush()
+
+  sys.exit(gyp.main(args))
+~~~~
+
+Most of this is just setup code. The two interesting bits are:
+
+  1. `args.append('-I%s/third_party/skia/gyp/common.gypi' % using_skia_src)`
+  1. `args.append(os.path.join(script_dir, '..', 'using_skia.gyp'))`
+
+In the case of 1, we're telling GYP to include (-I) the
+`src/third_party/skia/gyp/common.gypi` file which will define necessary
+variables for Skia to compile. In the case of 2, we're telling GYP that the
+main configuration file for our application is `src/using_skia.gyp`.
+
+The `src/using_skia.gyp` file is as follows:
+
+~~~~
+{
+  'targets': [
+    {
+      'configurations': {
+        'Debug': { },
+        'Release': { }
+      },
+      'target_name': 'using_skia',
+      'type': 'executable',
+      'dependencies': [
+        'third_party/skia/gyp/skia_lib.gyp:skia_lib'
+      ],
+      'include_dirs': [
+        'third_party/skia/include/config',
+        'third_party/skia/include/core',
+      ],
+      'sources': [
+        'app/main.cpp'
+      ],
+      'ldflags': [
+        '-lskia', '-stdlib=libc++', '-std=c++11'
+      ],
+      'cflags': [
+        '-Werror', '-W', '-Wall', '-Wextra', '-Wno-unused-parameter', '-g', '-O0'
+      ]
+    }
+  ]
+}
+~~~~
+
+There is a lot going on in there, I'll touch on some of the highlights. The
+`configurations` section allows us to have different build flags for our `Debug`
+and `Release` build (in this case they're the same, but I wanted to define
+them.)  The `target_name` defines the name of the build target which we'll
+provide to ninja. It will also be the name of the executable that we build.
+
+The dependencies section lists our build dependencies. These will be built
+before our sources are built. In this case, we depend on the `skia_lib` target
+inside `third_party/skia/gyp/skia_lib.gyp`.
+
+The include_dirs will be added to the include path when our files are built.
+We need to reference code in the config and core directories of Skia.
+
+`sources`, `ldflags` and `cflags` should be obvious.
+
+Our application is defined in `src/app/main.cpp` as:
+
+~~~~
+#include "SkPaint.h"
+#include "SkString.h"
+
+int main(int argc, char** argv) {
+  SkPaint paint;
+  paint.setColor(SK_ColorRED);
+
+  SkString* str = new SkString();
+  paint.toString(str);
+
+  fprintf(stdout, "%s\n", str->c_str());
+
+  return 0;
+}
+~~~~
+
+We're just printing out an SkPaint to show that everything is linking correctly.
+
+Now, we can run:
+
+    $ ./build/gyp_using_skia
+
+And, we get an error. Turns out, Skia is looking for a `find\_mac\_sdk.py` file in
+a relative tools directory which doesn't exist. Luckily, that's easy to fix
+with another entry in our DEPS file.
+
+    "src/tools/":
+        File((Var("googlecode_url") % "skia") + "/trunk/tools/find_mac_sdk.py@" +
+            Var("skia_revision")),
+
+Here we using the `File()` function of `gclient` to specify that we're checking
+out an individual file. Running `gclient sync` should pull the necessary file
+into `src/tools`.
+
+With that, running `build/gyp\_using\_skia` should complete successfully. You
+should now have an `out/` directory with a `Debug/` and `Release/` directory inside.
+These correspond to the configurations we specified in `using\_skia.gyp`.
+
+With all that out of the way, if you run:
+
+    $ ninja -C out/Debug using_skia
+
+The build should execute and you'll end up with an `out/Debug/using\_skia` which
+when executed, prints out our SkPaint entry.
+
+Autorun GYP
+-----------
+
+One last thing, having to run `build/gyp\_using\_skia` after each sync is a bit of
+a pain. We can fix that by adding a `hooks` section to our `DEPS` file. The `hooks`
+section lets you list a set of hooks to execute after `gclient` has finished the
+sync.
+
+    hooks = [
+      {
+        # A change to a .gyp, .gypi or to GYP itself should run the generator.
+        "name": "gyp",
+        "pattern": ".",
+        "action": ["python", "src/build/gyp_using_skia"]
+      }
+    ]
+
+Adding the above to the end of DEPS and running gclient sync should show the
+GYP files being updated at the end of the sync procedure.
+