design patterns summer course 2010-2011 - session#2

Session #6Muhamad Hesham

Day in Programmer`s Life

Agenda

State vs Strategy Day in Programmer Life GOF visit Project Description

Pattern’s Challenge Are they Twin patterns?

What are the differences between State and Strategy Pattern?

Our Target Game

Learning through Game Programming

Why Game Programming ?

2. Resource intensive software

3. Interactions till death

1.Fun & Interesting

4. Coding non-stopOOD & Design patterns in action

Our Target Game Platformer Skeleton

Main Actors • Level• Player• Enemy• Gem

Call for new requirement

Once the player collects a gem I want: Enemy increases its speed. Other gems change its color

to a random color.

First try for implementation

1. We need find the place in code where the gem is tested for being collected.

2. We need modify enemy speed.

3. We need modify gem color.

1. We expose private members to the public.

2. We are dependant on certain members.

3. Each time we need modify the level code.

Without correct pattern Our code smells bad!

Call for new requirement

Once the player die I want: Enemies speed is reset. Other gems change its color

to black.

Call for new requirement

Each level can be in one of two styles: Pharonic Aztec

First level is Aztec. Second and third levels are

Pharonic.

First try for implementation

1. We need find where we decide which image we load.

2. Categorize images to 2 sets, Pharonic an Aztec.

Each time we add a new theme

we add piles of if-else statements.

Our class do more than its job

(SCSR).

Without correct pattern Our code smells bad!

Call for new requirement

My nephew has another opinion First level is Pharonic. Second level is Aztec Third level is random.

Call for new requirement

I want the enemy turn crazy when you collect a gem.

If you touch the enemy while it is crazy, you die and it turns idle again.

Increase crazy enemy speed by 4 times.

First try for implementation

What do you think we need do this time ?

Violates Open Closed Principle.

Further additions will cause bugs.

State transitions are buried between if-else.

Without correct pattern Our code smells bad!

Original Enemy State Machine

Running Idle

reach cliff

after a while

Updated Enemy State Machine

Running Idle

reach cliff

after a while

Crazy

gem collectedgem

collected

player died

Call for new requirement

I want …

Go to HELL !!!

GOF Visit: Authors

GOF Visit: Organization

Let`s ask the

authors

It is Project Time!

Thank you ...

Questions??mhesham.fcis@gmail.com