TL;DR:

  sudo apt-get build-dep unity-2d
  cmake .
  make -j4 && (killall unity-2d-shell; sleep 1; killall unity-2d-shell; sleep 1 && ./shell/app/unity-2d-shell &)


Longer version

To build trunk:

 1. Install build dependencies (on Ubuntu):

  apt-get build-dep unity-2d

 2. Qt/QML preprocessing/preparation stage (the '.' is essential):

  cmake .

 3. Compile (in parallel on four CPUs):

  make -j4

 4. Test:

  killall unity-2d-shell
  killall unity-2d-shell
  ./shell/app/unity-2d-shell &

 To do iterative compile+test, you can use the command:

  make -j4 && (killall unity-2d-shell; sleep 1 && ./shell/app/unity-2d-shell &)

 (A double killall is only needed the first time after session
 login.  This is to break the default automagic respawn cycle).

 5. Test again with non-compositing window-manager mode (eg. different assets
  such as './shell/common/artwork/desktop_dash_background_no_transparency.sci'):
  
  killall unity-2d-shell
  killall unity-2d-shell
  metacity --replace --no-composite

 6. Restore compositing mode:

  killall unity-2d-shell
  killall unity-2d-shell
  metacity --replace --composite

  (The double killall is to defeat the auto-respawn)


Debugging output:

 a. From Qt C++ code:

  qDebug() << "foobar=" << foobar;

Finally:

If you want to propose your changes for merging back into the main tree, see:

  http://wiki.ubuntu.com/Unity2D#Coding


Have fun!  -Paul Sladen, 2012-02-24 from advices of the DX team!