Wednesday, 13 November 2013

Designing a Software System

This is the first guest post on my Blog, this one comes from a PhD student (and previously an MSc at Bournemouth) Mathieu Sanchez.

This post is specifically aimed at the design of complex software systems and is in general feedback on how to so the initial design required for some of our assignments. I was really impressed with this email and decided to share it with everyone.

Design often takes experience, which is why it is so difficult to teach, but there are some "half rules".
  • Write down your concepts, keywords and actions on a piece of paper, there is no need to draw anything. Verbs often translate to a relation and/or a class method (important). Nouns often refer to a class. ( see this and this)
  • Classes are most likely a singular noun. If it is not then maybe you are doing something wrong. In this case, check your multiplicity, and try to find a better name. It can happen that you have "container" classes. Don't name them by what they contain. An example would be a container for several wolves. If you name it wolves, it is unclear, and will lead to confusion. Do you mean a "pack of wolves"? Naming is very important, and will help you get a clearer vision, and help the markers (which is always good).
  • Classes ending in -ER  are a warning flag. It can happen, but if it does, you need to be sure of yourself. Once again, naming might be the issue, not the actual design. (see here here and here)
  • Don't build crazy associations everywhere. Data can travel along an association and should have a strong meaning such as "owns" "directs" etc...
  • Triangle relations are nasty. If you have class A, B and C, there should not be a link between each of them with each other. 
  • If you find that there are many ways to achieve the same task, then there might be some inheritance in there. For instance, shadows in rendering can be done through shadow mapping or shadow feelers. This is crying for inheritance. Make sure you have a look at Liskov substitution if you have inheritance.
  • Many of the common problems are solved with (famous) patterns. For instance, if there are two ways of doing one operations, but can also be combined together to achieve a better result, then there is a pattern for that.
  • When I read a diagram, I first look for a point of entry. And so should you. A point of entry for me is where everything starts, the class that controls the entire system. If it is unclear to you where it starts, then you might have missed something.
  • Think at a higher level at first, don't go straight for details, in fact implementation details such as acceleration structures only come last. The first diagram gives an overview of the system. If the interfaces are correctly made, adding spatial data structures is a piece of cake.
  • Think about extensibility. What if someone else wants to extend your library/system? If I have to jump into your code to add some if/else and edit your interface, then it is just plain wrong. Hence inheritance and factories.

Finally, once you have a draft, you need to review your diagram. The only thing I do when I try to help you is ask you my famous "what is its responsibility, in one and only sentence?". 

Do it yourself. Once the diagram is under your eyes, you can see if one of the classes overlaps with another, or worse, there is no class for a particular class. Then, double check your multiplicity. Read it out loud if needed. You should have two sentences to read. Let s say we have  [ A ] 1 ------- * [ B ], then it would read "A has many B, and B belongs to one and only one A". Multiplicity can be: 0..1 (at most one), 1 (one and only one), 0..* (any number), 1..* (one or more). Your inheritance should be solid if it respects the Liskov substitution principle.

Don't leave your diagrams without explanation, and stand your ground. Design is all about making decisions and trade-offs. I want to know those, because this is what lets me know if you actually worked on this, and are an able analyst, or if you are just fighting to just get a working system.

Wednesday, 2 October 2013

Introduction to using the bash shell (NCCA Version)

So it's the first week of term, and many new students have arrived to start their lab sessions only to find that we don't use windows!

There are many reasons for this, however the main one is the our main output industry is VFX and the majority of (large) VFX houses use linux / unix. This is due to a number of reasons, however mainly stability, scalability and ease of customisation.

Learning to use the linux command line and linux in general is quite a daunting task for a new user, and many people often wonder why they should bother when there is a perfectly good GUI. However as I shall explain in the following videos it will make you a more efficient / better operator if you can master some of the basic shell commands.

Also it has the added benefit that once you have learnt them, most of them will also be available in both shell scripts, python programs and C / C++ programs so you are learning valuable transferable skills all in one go.

Whilst these videos will concentrate on the university lab setup they will also be relevant to other linux distributions and linux in general and are mainly a repetition of what we do in the introduction lab sessions.

There is a link to a workbook and other resources here


(for more info on ssh see here)

alias ls='ls --color'
alias ll='ls -al'
alias rm='rm -i'

some useful information on the prompt

Friday, 30 August 2013

Getting Started with GamePlay3D under Mac OSX

I've been researching different game engines to use with our teaching next year. Of the many engines gameplay3D stood out for a number of reasons.
  1. Open Source
  2. Written in C++ and Lua scriptable
  3. Works under Mac, Linux, Windows and mobile devices
This blog post is going to talk about the basic setup under mac osx and how to start a basic project, In this case I'm going to use xcode, however I do also have a basic qt creator project as well which I may do in another blog post.

Downloading the source

I'm going to download the source using git into my main root directory as this will make paths easier. To do this I do the following
git clone
This may take a while but once it is done you should have a new directory called $(HOME)/GamePlay. Now we have to download the external dependancies. This is done via a script called Change into the GamePlay directory and run this script. This will take a while as it is quite a large file but it will download pre-built libs for all the platforms. Under mac osx these are built as 32bit static libs and may cause problems if you wish to link against other 64bit libs and I will do another blog post at a later date on how to build and link your own 64 bit version of the library but it is quite an involved process. In most cases the 32bit pre-built lib will be fine.

Compiling with xcode

Now we can open the xcode workspace (gameplay.xcworkspace) and configure and build the main gameplay static library.

To make development easier I'm going to setup the targets to build the library in the same root GamePlay directory. To do this we do the following first goto File->Workspace Settings in the xcode menu

Choose WorkSpace relative as shown below

Now we can build the library and the final lib should be placed in the directory GamePlay/DerivedData/gameplay/Build/Products/Debug. This actually builds a mac framework that we can copy into some other directory to use in our own projects. However for now we will leave it as it is.

Creating a new project

Gameplay comes with a newproject script that will copy a template project to a new location. Again I have modified this to make it easier to create new projects in directories other than the main GamePlay one. 

In an editor open up the GamePlay/ script look for each instance of the cp command like this
cp "template/template.vcxproj" "$projPath/$projName.vcxproj"
Where it says "template/ we are going to pre-pend the path of the GamePlay install so in my example it's going to be $HOME/GamePlay/
cp "$HOME/GamePlay/template/template.vcxproj" "$projPath/$projName.vcxproj"
Do this for every cp command in the script.

Now this is done we can create a new directory to put our demos in. In my case I've created one called GamePlayDemos

mkdir GamePlayDemos
cd GamePlayDemos

1. Enter a name for the new project.

   This name will be given to the project
   executable and a folder with this name
   will be created to store all project files.

Project Name: Test

2. Enter a game title.

   On some platforms, this title is used to
   identify the game during installation and
   on shortcuts/icons.

Title: Test

3. Enter a short game description.


4. Enter a unique identifier for your project.

   This should be a human readable package name,
   containing at least two words separated by a
   period (eg. com.surname.gamename).

Unique ID: ncca

5. Enter author name.

   On BlackBerry targets, this is used for
   signing and must match the developer name
   of your development certificate.

Author: jm

6. Enter your game's main class name.

   Your initial game header and source file
   will be given this name and a class with
   this name will be created in these files.

Class name: Test

7. Enter the project path.

   This can be a relative path, absolute path,
   or empty for the current folder. Note that
   a project folder named Test will also
   be created inside this folder.

Once the script has run you should see a folder like this
Now we can open the Test.xcodeproj file and get ready to build the demo. First we need to change the search paths for headers. By default they look like this
We need to add $(HOME)/GamePlay to each of these paths (or the directory you installed it into)
This will now allow the project to compile, however we still need to set the linker paths and do the same path addition

Add $(HOME)/GamePlay to the ../ paths as shown

Finally we need to add an additional path for the libgameplay.a location this can be done by selecting the build options and removing the original reference and locating the one we built earlier in the DerivedData directory as shown

The program should now run and give you the following screen.

I will do some more blog posts soon on using the game engine with maya.

Saturday, 11 May 2013

GLSL tessellation Shaders under Mac OSX

So this interesting post appeared the other day saying that tessellation shaders were working  on Mac OSX. According to the documents and other things like GLView this is not the case.

I decided to spend the day investigating the claims to a) see if they were true, and b) see how I could replicate this in my own library.

The following video shows how I used the Mac OpenGL profiler to dig into the source code and find out how to do this.

 The main code elements you need are the following defines

#ifdef DARWIN
        #define GL_TESS_CONTROL_SHADER 0x00008e88
        #define GL_TESS_EVALUATION_SHADER 0x00008e87
    #ifndef GL_PATCHES
        #define GL_PATCHES 0x0000000e
Once this has been defined somewhere you can use the default OpenGL commands to create a shader, I chose to use the demo code / shader here the main thing to remember is that you must use GL_PATCHES to draw to the tessellation units.

The other problem is that code like
glPatchParameteri(GL_PATCH_VERTICES, 16); 
is not available as the glPatchParam functions are not exposed, the good news is that you can set all of this in the shader so it is not too much of an issue. The updates have now been rolled into the core ngl library, and I will add some demos soon.

Friday, 3 May 2013

Install NGL / Qt on a new Mac

This video blog shows how to install all of the NGL environment on a brand new mac running Mountain Lion. The links to download qt are here and the main configuration for ngl etc is here.

This is how I set the alias for qt creator
export PATH=$PATH:/Users/jmacey/Qt5.0.2/Qt\
alias qtcreator='Qt\ Creator'

Next you need to follow the instructions here to install and setup NGL, you will need to install bzr which is a simple package from here.
Finally this example shows how to build the Qt 5 version of NGL and a basic demo

Monday, 11 March 2013

Adding Movement in ngl

This video blog shows how to add movement using the Model, View, Project matrix in ngl you can get the demo program here and should also read the lecture notes here

Thursday, 14 February 2013

When it all goes wrong!

It's that time of year again, (no not Valentines day). Students have finally realised that they have assignments to do and are finally testing and writing code!

So far today I've had 12 email (and this week about 30) with problems and errors, so I've decided to collate as much wisdom and help as I can here which hopefully will help not only you but also me!

This post is intentionally sarcastic and not aimed at anyone in particular!


A lot of the time the errors are quite easy to spot but you get the blind panic of it not working, first thing you should do is "read the (fine) error message".

In the following example
src/GLWindow.cpp: In member function 'void GLWindow::persp(GLWindow::MODE)':
src/GLWindow.cpp:256: error: expected ',' or ';' before 'm_transformStack'
make: *** [obj/GLWindow.o] Error 1
In this case we can read that there is an error in the file src/GLWindow.cpp at line 256 so I would suggest looking there!

As I'm using (and most of you are) QtCreator we only have to double click on the error message to goto the error. Even better it also underlines it in red! (BTW green underlined usually indicates unused variables so we can remove them as well) and yes in this case I've missed a ;

Now some errors are not as obvious and I will add a list of the common ones as I get sent them at the bottom of this post. 

Different Error types

It is important to differentiate between error types.  We can roughly split the errors into three categories.
  1. Compilation errors
  2. Linker errors
  3. Runtime errors
Compilation errors are the most common and may be due to many different factors, some can be due to a missing header / include such as
src/main.cpp: In function 'int main(int, char**)':
src/main.cpp:11: error: 'MainWindow' was not declared in this scope
src/main.cpp:11: error: expected `;' before 'w'
src/main.cpp:13: error: 'w' was not declared in this scope
make: *** [obj/main.o] Error 1
In this case we are just missing the #include "MainWindow.h" but the error seems worse, the clue is the "not declared in this scope" which should give you a hint that the compiler doesn't know about something. Another error along the same lines is the following
int main()
  std::cout<<"hello world\n";
In this case we get the error
1.cpp: In function 'int main()':
1.cpp:3: error: 'cout' is not a member of 'std'
Just because we are missing the #include <iostream>. When you do get these errors this is a good resource for finding out what has gone wrong as is this

Linker errors are harder to find but usually are due to the fact that you don't have the correct libraries installed, the also seem much more scary as they seem to go on forever in some cases

For example the following
clang++ -Wall -g ClearScreen.cpp -o ClearScreen `sdl-config --cflags`
Undefined symbols for architecture x86_64:
  "_SDL_FillRect", referenced from:
      clearScreen(SDL_Surface*, char, char, char) in ClearScreen-vFrFBN.o
  "_SDL_Flip", referenced from:
      clearScreen(SDL_Surface*, char, char, char) in ClearScreen-vFrFBN.o
  "_SDL_Init", referenced from:
      _SDL_main in ClearScreen-vFrFBN.o
  "_SDL_MapRGB", referenced from:
      clearScreen(SDL_Surface*, char, char, char) in ClearScreen-vFrFBN.o
  "_SDL_PollEvent", referenced from:
      _SDL_main in ClearScreen-vFrFBN.o
  "_SDL_Quit", referenced from:
      _SDL_main in ClearScreen-vFrFBN.o
  "_SDL_SetVideoMode", referenced from:
      _SDL_main in ClearScreen-vFrFBN.o
  "_SDL_WM_SetCaption", referenced from:
      _SDL_main in ClearScreen-vFrFBN.o
  "_main", referenced from:
     -u command line option
     (maybe you meant: _SDL_main)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
This is due to the fact that the compiler is not using the SDL libs flags "-L/usr/local/lib -lSDLmain -lSDL" Once these are added it usually fixes things. One of the most difficult problems you will encounter is finding which function lives in which lib, again you can google. Or I have a handy shell script
for f in *.a *.so *.dylib
  echo "checking for $1 in - $f"
  strings $f | grep $1
Which using glVertex in the directory /usr/lib/ gives glVertex | more
checking for glVertex in - libGLEW.a
Runtime errors are usually created when we cant find the dynamic libs we need to link to, for example
dyld: Library not loaded: libNGL.1.0.0.dylib
  Referenced from: /Volumes/home/jmacey/teaching/NGL5Demos/SimpleNGL/./SimpleNGL
  Reason: image not found
Trace/BPT trap: 5
Means that the LD_LIBRARY_PATH (actually DYLD on mac) has not been set for the NGL lib (see here)

If in doubt make clean

Sometimes things get out of sync and dependancies are not re-read. The simplest solution is to do a qmake; make clean ; make;l

In QtCreator this is the same as doing a re-build all. You will be surprised how often this solves things (usually to deps not being updated)

Still Stuck do this

If you need to send me some errors, please don't do this 
Yes that is an iPhone photo of the error message on my monitor, yes I have had this mailed to me before, and no I can't figure out what is wrong! My eyesight used to be that good but not anymore!

This is not much better
Yes I can see the errors in this one but it still doesn't help much, I really need to see the compiler output / flags as well as the error messages (these are on different tabs on Qt).

The easiest way of sending me errors etc is via plain ASCII text (I'm old fashioned like that ;-) To do this will require a little typing.

cd [your project root]
make &>err.txt

If you do this in the root of the project where the makefile is it will run make and output all of the errors to the file err.txt. Mail it to me as this will then help me to find the errors.

Send me the code

If I ask you to send me the code, I only need the source and other files not the .o and exe. The easiest way of sending this to me is as follows

cd [your project root]
make distclean
cd ..
tar vfcz code.tgz [your project root]

Then mail me the code, it also helps if I have the following information
  • Operating System (and version if Mac or Linux)
  • Compiler used (use g++ -v or clang -v) 
  • Graphics Card Make Model and version of OpenGL drivers installed. 
  • Versions of any extra libs etc you may be using. 
A lot of the time this could be the cause of the problem, I will test all my code against Mac OSX (Mountain Lion) using

clang++ ( Apple clang version 4.0 (tags/Apple/clang-421.0.60) (based on LLVM 3.1svn) Target: x86_64-apple-darwin12.2.0 Thread model: posix)

and the lab build

clang++ -v clang version 3.2 (trunk 163783) Target: x86_64-unknown-linux-gnu Thread model: posix g++ -v Using built-in specs. Target: x86_64-redhat-linux Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl= --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj- --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux Thread model: posix gcc version 4.4.6 20120305 (Red Hat 4.4.6-4) (GCC)

Also make sure you have pulled the latest versions of any of my code using a bzr pull as I do bug fixes as they are reported (there will soon be a more official way of reporting this using the redmine system)

Some Common Errors (and Fixes)

I get quite a lot of common errors so I will try and list them here

GLEW Errors

If you get something like this
/usr/include/GL/glew.h:84:2: error: gl.h included before glew.h
#error gl.h included before glew.h
/usr/include/GL/glew.h:90:2: error: glext.h included before glew.h
#error glext.h included before glew.h
It is due to the GLEW libs not being included properly (you may also get lots of PFNGL..... errors as well) Some of the old versions of my .pro files have a subtle bug in them where the defines are not done correctly check the .pro file and make sure this is correct
            DEFINES += LINUX
            LIBS+= -lGLEW
linux-clang* {
              DEFINES += LINUX
              LIBS+= -lGLEW

xxx does not name a type

Errors such as include/GLWindow.h:50: error: ‘Vector’ in namespace ‘ngl’ does not name a type means that you have either not included the correct header or something is missing. In this case it is due to the fact that ngl::Vector has now been replaced with ngl::Vec3 so you will need to #include <ngl/Vec3.h> and also replace all versions of ngl::Vector with ngl::Vec3

Thursday, 24 January 2013

CA 1 Initial Design General Feedback

This is the general feedback for the CA1 Initial Design in addition to some of the comments here

Class Diagrams

A lot of the class diagrams didn't use standard UML format. This is quite important as I can then see a number of things about the class at a glance. There are more details in my lecture notes but these slides show the main things

I mentioned in a lot of the feedback that you need to show the multiplicity / associations of the classes. This can be done as shown

Associations and Containment

In a lot of the designs there are classes that show some sort of relation, however no mention of a container is shown in the attributes.
In this case we use a filled diamond and it always gives a multiplicity of 1 or 0 .. 1, this implies ownership and when the car is destroyed so it the Engine, this is broadly know as composition.

Aggregation differs from composition as it doesn’t necessarily imply ownership. This is usually implemented by containing a reference to another object where the lifetime is determined elsewhere.


Those of you that mentioned doing some form of physics need to look at two things. Once getting a time into your program. This can be done easily in Qt using the QTimer classes. There are several NGL demos that use this and you can see how in the code.

The other thing you will need to write is an integrator.  If you code is well designed this should be able to be replaced with different types. I suggest starting with a basic Euler integrator then progress to a more stable RK 4 integrator

If you are not writing your own Physics but need to do some basic physics for a game there are a number of solutions, the labs have both ODE and Bullet installed and there is already an ODE demo for NGL with a bullet one coming soon.

If you are doing a 2D game or a basic 2.5D platform I would suggest Box2D as it is much simpler and more suited to these style of game. 


If you are writing an L-System I would suggest reading "The algorithmic beauty of plants". For a general design I would suggest reading in your grammar rules from a text file (you get marks for this anyway). There is a basic parser framework in the lecture code here and you can use boost::tokenize to most of the hard work.

It is also important to only build the grammar up once and create the geometry and store it. As this is a recursive system the generation may be slow and adding in drawing will make this a really slow system once a few iterations are used. The system should only update when a parameter is changed and this should generate geometry to be drawn every frame and not the other way around.

Also start in 2D and generate a simple turtle class, this can later be upgraded to a 3D system once the basic system is working.

Flocking System

One of the hardest problems with a flocking system is managing the communication between the boids. All of the boids need to know where they are in the world as well as have some knowledge of each other.  It is possible to use a naive list and check each boid against the others however this will lead to an O(n^2) complexity and slow things down. 

For the initials test this will be ok, however it should be factored into the design that at some stage this may become a problem at a later stage.

To get the flock working initially start with the flock centre rule. If you add the position of all the boids and divide by the number of boids this will give you the centroid. You can then calculate the direction vector for the flock centre on a per boid basis.

The other basic rules can then be added. It is also a good idea to add a weight to each of the rules and see the different effects. This can be loaded in a text file (or using a GUI) .

Next Steps

You should have a basic design, re-visit it based on the comments above and see what is missing. Once you have done this you should start to write the classes. I usually create the basic classes so they can be instantiated and connected together. Once this is done start adding the functionality as required.

For a more in detail step by step guide look as the examples from last year here note that some of the data types from these examples have changed but the principles are still the same.

Good luck and if you have any more questions ask me in the lab.