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Load a green ball image in the topmost Sprite object

Listing 11 calls the SetImage method to change the image in the topmost sprite at the end of the run from a blue ball to a green ball.

Listing 11 . Load a green ball image in the topmost Sprite object.

if(frameCnt == moveLim) { sprites[0].SetImage("greenball",Content); }//end if

This capability would be useful, for example to change a sprite's image into a fireball in the event of a collision with another sprite.

Maintain the frame counter

The code in Listing 12 keeps track of the count of the first moveLim iterations of the game loop.

Listing 12 . Maintain the frame counter.

if(frameCnt<moveLim) { frameCnt++;}//end if base.Update(gameTime);}//end Update method

The end of the overridden Update method

Then Listing 12 makes the required call to the Update method in the superclass and signals the end of the method.

The overridden Game1.Draw method

The overridden Game1.Draw method is shown in its entirety in Listing 13 .

Listing 13 . The overridden Game1.Draw method.

protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue);spriteBatch.Begin(); //Draw all sprites.for(int cnt = 0;cnt<sprites.Count;cnt++) { sprites[cnt].Draw(spriteBatch); }//end for loopspriteBatch.End(); base.Draw(gameTime);}//end Draw method //-------------------------------------------------//}//end class }//end namespace

Draw all Sprite objects

After calling the SpriteBatch.Begin method and before calling the SpriteBatch.End method, Listing 13 uses a for loop to call the Sprite.Draw method on every Sprite object whose reference is stored in the list, passing a reference to the SpriteBatch object as a parameter in each call.

Call the SpriteBatch.Draw method

This causes each object to execute the single statement belonging to the Draw method shown in Listing 4 . Thus, the code in Listing 13 causes each Sprite object to call the SpriteBatch.Draw method to draw itself at the position specified by the current value of its Position property.

Note that there are three different methods named Draw being used here:

  • Game1.Draw
  • SpriteBatch.Draw
  • Sprite.Draw

The end of the Game1.Draw method

After calling the SpriteBatch.End method, Listing 13 makes the required call to the superclass' Game.Draw method and then signals the end of the Game1.Draw method. Listing 13 also signals the end of the class and the end of the program.

Run the program

I encourage you to copy the code from Listing 14 and Listing 15 . Use that code to create an XNA project. Compile and run the project. Experiment withthe code, making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.

Run my program

Click here to download a zip file containing my version of the program. Extract the folder named XNA0126Proj from the zip file and save it somewhere on your disk. Start Visual C# 2010 Express and select Open Project... from the File menu. Navigate to the project folder and select the file with the extension of .sln . This should cause the project to open and be ready to run or debug as described in the earlier module titled Getting Started .

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Source:  OpenStax, Xna game studio. OpenStax CNX. Feb 28, 2014 Download for free at https://legacy.cnx.org/content/col11634/1.6
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