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This method receives a list of Sprite objects as an incoming parameter. It tests for a collision with each sprite in the list beginning withthe sprite at the head of the list. If it detects a collision with a sprite, it stops testing immediately and returns a reference to the Sprite object for which it found the collision. If it doesn't find a collision with anysprite in the list, it returns null.
The new method named IsCollision begins in Listing 5 .
Listing 5 . Beginning of a new IsCollision method.
public Sprite IsCollision(List<Sprite>target) {
Rectangle thisRectangle =new Rectangle((int)(position.X),
(int)(position.Y),image.Width,
image.Height); The code in Listing 5 constructs a new Rectangle object that describes the rectangular area currently occupied by the sprite's imagerelative to the upper left corner of the game window. The Rectangle object's reference is saved in the local variable named thisRectangle .
Listing 6 begins by declaring a pair of local variables named targetRectangle and cnt .
The variable named targetRectangle will be used to store a reference to a rectangular area that currently contains a target sprite. Thevariable named cnt will be used as a loop counter.
Listing 6 . Test for a collision with other sprites.
Rectangle targetRectangle;
int cnt = 0;while(cnt<target.Count){
targetRectangle = target[cnt].GetRectangle();
if(thisRectangle.Intersects(targetRectangle)){return target[cnt];}//end if
cnt++;}//end while loop
return null;//no collision detected}//end IsCollision Then Listing 6 executes a while loop that:
Executing a return statement in the middle of the while loop terminates the loop and also terminates the method.
If no collision is detected, the loop terminates when all of the Sprite objects in the list have been tested.
At that point, Listing 6 executes a different return statement to return null and terminate the method. The null value is returned in place of a reference to a Sprite object to signal that no collision was detected.
Listing 6 signals the end of the IsCollision method, which is also the end of the changes made to the Sprite class. Once again, you will find a complete listing of the new Sprite class in Listing 14 near the end of the module.
I will explain only those portions of the Game1 class that are substantially new to this program. You will find a complete listing ofthe Game1 class in Listing 15 near the end of the module.
The only code that is substantially new prior to the LoadContent method is the declaration of an instance variable of type Sprite named spiderWeb . Therefore, I will skip down and begin my discussion with the overridden LoadContent method, which begins in Listing 7 .
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