Adding Skia Debugger documentation

site/dev/tools/debugger.md

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+Skia Debugger
+=============
+
+Introduction
+------------
+
+The Skia Debugger is a graphical tool used to step through and analyze the
+contents of the Skia picture format. Pre-requisites include installing the Qt
+Library and downloading the Skia code base.
+
+Qt is available here: http://qt-project.org/downloads.
+
+It can also be installed on linux using 
+
+<!--?prettify?-->
+~~~~
+sudo apt-get install libqt4-dev
+~~~~
+
+Note that the debugger has been tested with Qt 4.8.6; it is known not to work
+with Qt 5.0RC1 on the Mac.
+
+Design Documents:
+
+https://docs.google.com/a/google.com/document/d/1b8muqVzfbJmYbno9nTv5721V2nlFMfnqXYLNHiSQ4ws/pub
+
+
+How to build and run
+--------------------
+
+Because the debugger uses Qt, you'll need to build skia in 64 bit mode:
+
+<!--?prettify?-->
+~~~~
+cd trunk
+./gyp_skia
+GYP_DEFINES="skia_arch_width=64" make debugger
+out/Debug/debugger
+~~~~
+
+For Windows, Qt ships as 32 bit libraries so to build and run one should just be
+able to:
+
+<!--?prettify?-->
+~~~~
+cd trunk
+make clean gyp
+<open solution in VS2010 and build everything>
+~~~~
+
+Depending on how your Qt is installed you may also need to define an environment
+variable like: 
+
+~~~~
+GYP_DEFINES=qt_sdk='C:\Qt\4.8.6\'
+~~~~
+(which needs to be set before you execute 'make gyp')
+
+On Windows, you may need to copy several DLL and PDB files from %QTDIR%\bin into
+your executable directory (out/Debug or out/Release):
+
+QtCore4.dll QtCored4.dll QtCored4.pdb
+
+QtGui4.dll QtGuid4.dll QtGuid4.pdb
+
+QtOpenGL4.dll QtOpenGLd4.dll QtOpenGLd4.pdb 
+
+
+Producing SKPs for usage
+------------------------
+
+You may either use the Skia testing images (GMs) for use in the debugger or
+create your own via chromium.
+
+To create SKPs from Chromium you must download and build chromium on your
+platform of choice: http://www.chromium.org/Home
+
+<!--?prettify?-->
+~~~~
+cd src
+make chrome
+out/Debug/chrome --no-sandbox --enable-gpu-benchmarking --force-compositing-mode
+~~~~
+
+After which go to Tools, Settings, Javascript Console and type:
+
+<!--?prettify?-->
+~~~~
+chrome.gpuBenchmarking.printToSkPicture(dirname)
+~~~~
+
+Using the Debugger
+------------------
+
+The debugger is fairly straight forward to use once a picture is loaded in. We
+can step through different commands via the up and down keys, and clicking on
+the command in the list. We can pause execution of commands with the pause
+button in order to inspect the details of the command in the inspector tabs
+down below.
+
+ 
+ Command      | Function
+ -------------|-----------------------------------------------
+ x            | toggles the visibility of the selected command
+ alt-x        | clears all hidden commands
+ ctrl-x       | shows all deleted commands
+ b            | creates a breakpoint on a command
+ alt-b        | clears all breakpoints
+ ctrl-b       | shows all breakpoints
+ ctrl-r       | rewinds the picture to the first command
+ ctrl-p       | plays to the next breakpoint or last command
+ ctrl-i       | Toggles the inspector and settings widgets
+ ctrl-d       | Toggles the directory widget
+ space        | Pauses drawing execution
+ ctrl-o       | Opens a file dialog for loading pictures
+ ctrl-s       | Saves the skp if you deleted any commands
+ ctrl-shift-s | Saves the skp under the new specified name
+ ctrl-q       | Quits
+
+![Debugger interface](debugger.png)
+
+