Index

1. Programming Proverbs

• 18. ‘‘Use comments.’’
• Henry F. Ledgard, ‘‘Programming Proverbs: Principles of Good Programming with Numerous Examples to Improve Programming Style and Proficiency’’, (Hayden Computer Programming Series), Hayden Book Company, 1st edition, ISBN-13: 978-0810455221, December 1975.

2. Internals of PGE (Python)

• during this lecture we will start to look at the internals of PGE
• we will concentrate on the Python module python/pge.py
• we can see that this sits near the top of the various software levels of our game

• 

3. pge.py

• in the last lecture we saw how foreground and background objects are maintained in python/pge.py
• we also saw how objects were created and are checked at runtime for type consistency
• in this lecture we will examine how integrates with Pygame

4. Obtaining the source to pge

• open up and command line terminal and type:

• $ mkdir -p $HOME/Sandpit
  $ cd $HOME/Sandpit
  $ git clone https://github.com/gaiusm/pge

• the files for the pge package will be available in pge
  

5. Source directory structure of the pge package

• the key directories are:
• pge/c
  • C source code
• pge/m2
  • Modula-2 source code
• pge/i swig interface (PGE API definition)
• pge/python
  • python code, ( pge.py and Python tools, such as pgeplayback and max2code )

6. Key configuration files

• pge/configure.ac
  • source code for the classic configure command
• pge/Makefile.am
  • source code for Makefile in the top directory of the build tree
• pge/c/Makefile.am
  • source code for c/Makefile in the build directory
• pge/m2/Makefile.am
  • source code for m2/Makefile in the build directory

7. Building pge from source

• you can choose either Modula-2 or C

• $ cd $HOME/Sandpit
  $ mkdir -p build-pge
  $ cd build-pge
  $ ../pge/configure --enable-langc
  $ make

• in this case the pge package is built from > 90% of C source files
  

8. Testing your build

• one simple test is to run the trapped example

• $ cd $HOME/Sandpit/build-pge
  $ ./localrun.sh ../pge/examples/trapped/trapped.py
  

9. Revisiting pge/python/pge.py

• a potential problem surfaces during the development of pge and its integration with Pygame
• Pygame controls the input sources: keyboard, mouse, joystick
  • and output devices, screen, audio etc
• internally Pygame uses an event queue on which all input events (keypress, mouse button press) are posted
• events are meant to be read by the Pygame user application code
• in order for PGE to be integrated with Pygame we need to ensure that
  • a program does not block waiting for an input event
• otherwise the physics engine will be starved from updating itself in real time

10. The PGE event queue

• internally pge also maintains an event queue (different from the Pygame event queue!)
• the pge event queue is a time ordered list of future events
  • each event predicting what will happen in the future
  • it might be a draw frame event
  • or a collision event
  • or a timer activation event
• pge/python/pge.py coordinates the pge event queue and also the Pygame event queue (input source)

• 

• notice the different kinds of events
  • relative time ordered
• although there might be another collision event at, say, time (20+10+1) 31 there is no point predicting it as the event at time 30 might change the world
  

11. pge/configure.ac

• is the source file which builds the file pge/configure
• it is written in a language called autoconf which is compiled into a portable shell script
• autoconf allows you to specify dependancies such as the build machine must have certain tools: awk , cpp , c++ and make
  • and the build machine must also have the -lpth library
• it also allows you to add extra configuration arguments
  • ie pge can be built using C sources, or built from Modula-2
  • and one can enable maintainer mode (dont do this unless you know what you are doing!)

12. Example sections of pge/configure.ac

• AS_MKDIR_P(c)
  AS_MKDIR_P(m2)
  AS_MKDIR_P(python)
  
  LT_INIT
  ...
  AC_ARG_ENABLE([maintainer],
  [  --enable-maintainer    Turn on maintainer],
  [case "${enableval}" in
   yes) maintainer=true ;;
    no) maintainer=false ;;
     *) AC_MSG_ERROR([bad value ${enableval} for --enable-maintainer]) ;;
   esac],[maintainer=false])
  AM_CONDITIONAL([MAINTAINER], [test x$maintainer = xtrue])
  ...
  
  
  AC_HAVE_LIBRARY(-lpth)
  AC_SUBST([langm2])
  AC_SUBST([langc])
  AC_SUBST([maintainer])

• we can see that autoconf allows us to use a library of routines AS_MKDIR_P
• and also we can create our own code to drive an option in rule AC_ARG_ENABLE

Index

This document was produced using groff-1.22.