Game development

Space Invaders in C# and .NET

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Figure 1 - The Space Invader Game 
Yes, the classic arcade game has returned and is appearing in C# Corner complete with sound and authentic aliens and source code. It's not quite as good as the real game, but with a few adjustments it can get there. I actually got many of the sounds and images from a web site that is bent on celebrating this traditional ground breaking . This made writing the game a little bit easier since they supplied many of the files in which you can capture the images and sounds.
Playing the Game

This version is played using the left and right arrow keys to move the man and the space bar to fire. If you hit an alien, you get 10, 20, or 30 points, depending on which one you hit. If a bomb hits you, you die and you only have 3 lives. The shields will protect you from a bomb, so you can hide behind them while you wait for the bombs to pass. Occasionally, a saucer flies across the screen. If you hit it, you get a suprise score (up to 150 points). 
Design of the Game
The design for this game is shown below:


Figure 2 - Space Invader UML Design Reverse engineered using WithClass 2000

The Design basically has a base class GameObject which knows how to draw the game pieces bitmap.  Subclassed under this object is all the component classes of the game: Man, Invader,Bullet, Bomb and Shield. A row of Invader classes is controlled through the InvaderRow class. The form contains an array of  InvaderRows, an array of Shields, and a Man.
The Timer Event Handler

The entire game is played off of the timer component. After each tick of the timer, the game checks to see if their are bomb collisions, bullet collisions, and whether or not to move the invaders. It also handles the key presses from the user here so as not to change the timing of the game. If a key is pressed, it is remembered by the key press event, but nothing more happens in the key press event handler.  Below is the code executed with each entry into the timer event handler:
Listing 1 - The Timer Event Handler in the Form
private void timer1_Tick(object sender, System.EventArgs e)
{ // move the man according to keypressesHandleKeys();// Count each timer interval to use it as a reference for timing the gameTimerCounter++;// if the game is over, just invalidate and returnif (GameGoing == false)
{// Move the Invaders in place to make them look like they are clappingif (TimerCounter % 6 == 0)
MoveInvadersInPlace();
Invalidate();return;
}// if the bullet shot from the man is off the screen, turn it offif (TheBullet.Position.Y < 0)
{
ActiveBullet = false;
}// Fly the saucer every 200 intervalsif (TimerCounter % kSaucerInterval == 0)
{
InitializeSaucer();
PlaySoundInThread("8.wav", 1);
SaucerStart = true;
}// Move the saucer across the screenif (SaucerStart == true)
{
CurrentSaucer.Move();if (CurrentSaucer.GetBounds().Left > ClientRectangle.Right)
{
SaucerStart = false;
}
}// move invaders every timer interval according to the speed factorif (TimerCounter % TheSpeed == 0)
{ 
MoveInvaders();
nTotalInvaders = TotalNumberOfInvaders();// Change the speed of the Invader according to how many are leftif (nTotalInvaders <= 20)
{
TheSpeed = 5;
}if (nTotalInvaders <= 10)
{
TheSpeed = 4;
}if (nTotalInvaders <= 5)
{
TheSpeed = 3;
}if (nTotalInvaders <= 3)
{
TheSpeed = 2;
}if (nTotalInvaders <= 1 )
{
TheSpeed = 1;
}if (nTotalInvaders == 0)
{// All the invaders were killed// Start the game again at the next level (move the invader starting position down)InitializeAllGameObjects(false); // don't initialize scoreTheLevel++;
}
}// Test for bullet and bomb collisions and act appropriatelyTestBulletCollision();
TestBombCollision();// Paint all the game objectsInvalidate();
}
Painting the Game Components
The drawing of all the components is triggered by the Invalidate. Below is the paint event handler that paints all of the game elements:
Listing 2 - The Paint Event Handler in the Form
private void Form1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{ // get the graphics surfaceGraphics g = e.Graphics;// Draw the entire graphics surface blackg.FillRectangle(Brushes.Black, 0, 0, ClientRectangle.Width, ClientRectangle.Height);// Draw the manTheMan.Draw(g);// Draw the scoreTheScore.Draw(g);// Draw the Bullet shotif (ActiveBullet)
{
TheBullet.Draw(g);
}// Draw the Saucerif (SaucerStart)
{
CurrentSaucer.Draw(g);
}// Draw the Space Invadersfor (int i = 0; i < kNumberOfRows; i++)
{
TheInvaders = InvaderRows[i];
TheInvaders.Draw(g);
}// Draw the Shieldsfor (int i = 0; i < kNumberOfShields; i++)
{
Shields[i].Draw(g);
}
}