如何制作滚动的背景

示范如何通过SpriteBatch类绘制一个滚动的背景。源码下载

示例截图

绘制滚动的背景精灵

绘制滚动的背景精灵

  1. 创建game类。

  2. 加载资源,和如何绘制精灵中所讲的1-3步一样 。

  3. 加载背景纹理。

    private ScrollingBackground myBackground;
    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);
        myBackground = new ScrollingBackground();
        Texture2D background = Content.Load<Texture2D>("starfield");
        myBackground.Load(GraphicsDevice, background);
    }
  4. 确定背景纹理和屏幕的尺寸。

    纹理的大小可以由他的Height和Width属性获得,屏幕的大小可以使用图形设备的Viewport属性获得。

  5. 通过纹理和屏幕信息,将纹理的起点设置为纹理的中心,将屏幕的初始点设置为屏幕的中心。

    // class ScrollingBackground
    private Vector2 screenpos, origin, texturesize;
    private Texture2D mytexture;
    private int screenheight;
    public void Load( GraphicsDevice device, Texture2D backgroundTexture )
    {
        mytexture = backgroundTexture;
        screenheight = device.Viewport.Height;
        int screenwidth = device.Viewport.Width;
        // Set the origin so that we're drawing from the 
        // center of the top edge.
        origin = new Vector2( mytexture.Width / 2, 0 );
        // Set the screen position to the center of the screen.
        screenpos = new Vector2( screenwidth / 2, screenheight / 2 );
        // Offset to draw the second texture, when necessary.
        texturesize = new Vector2( 0, mytexture.Height );
    }
  6. 改变Update方法中背景纹理的屏幕位置来滚动背景。

    增加屏幕Y轴值的话,背景精灵以每秒100像素的速度向下移动。

    protected override void Update(GameTime gameTime)
    {
        ...
        // The time since Update was called last.
        float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds;
    
        // TODO: Add your game logic here.
        myBackground.Update(elapsed * 100);
    
        base.Update(gameTime);
    }

    Y轴值不能大于纹理高度,这样背景就可以在屏幕顶部和底部之间来加滚动了。

    public void Update( float deltaY )
    {
        screenpos.Y += deltaY;
        screenpos.Y = screenpos.Y % mytexture.Height;
    }
    // ScrollingBackground.Draw
  7. 用LoadContent和Update中计算的起点和屏幕位置来绘制背景。

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
    
        spriteBatch.Begin();
        myBackground.Draw(spriteBatch);
        spriteBatch.End();
    
        base.Draw(gameTime);
    }

    如果这个纹理不能覆盖屏幕,就会绘制另一个纹理,根据加载时创建的texturesize向量从屏幕偏移向量的位置减去纹理的高度。这将给你一个循环的错觉。

    public void Draw( SpriteBatch batch )
    {
        // Draw the texture, if it is still onscreen.
        if (screenpos.Y < screenheight)
        {
            batch.Draw( mytexture, screenpos, null,
                 Color.White, 0, origin, 1, SpriteEffects.None, 0f );
        }
        // Draw the texture a second time, behind the first,
        // to create the scrolling illusion.
        batch.Draw( mytexture, screenpos - texturesize, null,
             Color.White, 0, origin, 1, SpriteEffects.None, 0f );
    }

发布时间:2009/2/18 8:25:33  阅读次数:6620

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