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.


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