Thursday, November 25, 2010

Videogames Part 4: The First Game

This final part will be a quick tutorial on a basic program in XNA. The program will have an image bouncing of the edges of the window.

To start you'll need to create a new XNA windows project, should with Xbox, or WP7 but I'm focusing on the windows one right now. Once the project is created in the content section in the solution explorer right-click and add an existing item. Browse to any image (jpg, png or bmp preferably) and load it. This will be the image that will bounce in the program.
We add some variable:

        Texture2D theImage;                                           // our image (*.jpg, *.png *.bmp)
        Vector2 posImage = Vector2.Zero;                      // initial position of the image
        Vector2 velImage = new Vector2(150.0f, 150.0f); // velocity vector
        int MaxX, MinX, MaxY, MinY;                             //limits
Then in load content we need to load our image:

            theSprites = new SpriteBatch(GraphicsDevice);
            // load the images
            theImage = Content.Load("imageName");//note: no extension in the image name
            MaxX = device.Viewport.Width - theImage.Width;//calculate the horizontal limit
            MinX = 0;
            MaxY = device.Viewport.Height - theImage.Height;//calculate the vertical limit
            MinY = 0;
Now for the update, where we update our variables:

GamePadState theXbox = GamePad.GetState(PlayerIndex.One);
            KeyboardState theKeyboard = Keyboard.GetState();
            //a way for the user to exit the program with the keyboard or xbox controller.
            if (theXbox.Buttons.Back == ButtonState.Pressed || theKeyboard.IsKeyDown(Keys.Escape))
            // modify the image position with our velocity vector and the time.
            posImage += velImage * (float)gameTime.ElapsedGameTime.TotalSeconds;
            //chech for horizontal bounce
            if (posImage.X > MaxX)
                velImage.X *= -1;
                posImage.X = MaxX;
            else if (posImage.X < MinX)
                velImage.X *= -1;
                posImage.X = MinX;
            // check for vertical bounce
            if (posImage.Y > MaxY)
                velImage.Y *= -1;
                posImage.Y = MaxY;
            else if (posImage.Y < MinY)
                velImage.Y *= -1;
                posImage.Y = MinY;
 Finally in the draw, we tell the program what to draw in the screen:

            // draw the image
            theSprites.Draw(theImage, posImage, Color.White); //here white acts like transparent
You can download the full solution here. It was made in VS2010 so you'll need VS2010 to open it. Also check a friend's blog for another XNA tutorial here. Note his blog is in spanish, but the code is universal :D

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