Qt GUI Files and CMake

Previously, new header or source files were added to the list of header and source files in the CMake build file CMakeLists.txt.  Qt form files (with the .ui extension) and header files containing the Q_OBJECT macro are handled differently.

The Q_OBJECT macro is added to any class definition that contains Qt's C++ extensions for defining signals and slots, which are class sections in additional to the normal private, public and protected sections.  These are handled by Qt's Meta-Object Compiler (moc), which produces a special MOC source file from the header file.  For mainwindow.h, the special source file produced is moc_mainwindow.cxx, which then gets compiled and linked into the program.

In the CMake build file, this is handled by the qt4_wrap_cpp command that is added as part of the Qt4 CMake module.  It is given a list of MOC source files and produces a list of MOC output source files.  This output list is then specified as a dependency to the output executable.  When a header file is included in the MOC sources list, it does not also need to be specified in the list of [normal] header files.

Qt form files are generated as an XML like language.  This file needs to be converted into a class definition (within a header file) so that it can be used by the C++ code.  These conversions are handled by Qt's User Interface Compiler (uic), which produces a special header file from the form file.  For mainwindow.ui, the special header file produced is ui_mainwindow.h, which contains the Ui_MainWindow class.  This source file is then included by the mainwinow.h header file.

In the CMake build file, this is handled by the qt4_wrap_ui command.  It is given a list of form UI files and produces a list of user interface header files.  This output list is then specified as a dependency to the output executive.

All of the generated files are placed in the CMake build directory, the same directory where the auto-generated header files (from the awk scripts) are placed.  This directory (the project binary directory) is specified in the include_directories command, so that the C++ compiler can find all of these generated files.  It is also no longer necessary to specifically check for an in-source build to not add this directory because the conflict no long exists between the system string.h header file (not used) and project string.h header file (removed).

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