了解BufferStrategy

Question

我是java的新手。我想做一个游戏。经过大量的研究，我无法理解缓冲策略的工作原理。 我知道基础知识..它会创建一个离屏图像，以后可以将其放入windows对象中..我得到了这个

public class Marco extends JFrame {
    private static final long serialVersionUID = 1L;
    BufferStrategy bs; //create an strategy for multi-buffering.

    public Marco() {
       basicFunctions(); //just the clasics setSize,setVisible,etc
       createBufferStrategy(2);//jframe extends windows so i can call this method 
       bs = this.getBufferStrategy();//returns the buffer strategy used by this component
    }

   @Override
   public void paint(Graphics g){
      g.drawString("My game",20,40);//some string that I don't know why it does not show
      //guess is 'couse g2 overwrittes all the frame..
      Graphics2D g2=null;//create a child object of Graphics
      try{
         g2 = (Graphics2D) bs.getDrawGraphics();//this new object g2,will get the
         //buffer of this jframe?
         drawWhatEver(g2);//whatever I draw in this method will show in jframe,
         //but why??
      }finally{
         g2.dispose();//clean memory,but how? it cleans the buffer after
         //being copied to the jframe?? when did I copy to the jframe??
      }
      bs.show();//I never put anything on bs, so, why do I need to show its content??
      //I think it's a reference to g2, but when did I do this reference??
   }

   private void drawWhatEver(Graphics2D g2){
       g2.fillRect(20, 50, 20, 20);//now.. this I can show..
   }
  }

我不知道..我已经研究了这个很长一段时间..而且根本没有运气..我不知道......也许它就在那里，而且它非常简单明了我看起来太傻了......

感谢所有帮助.. :)）

Answer 1

以下是它的工作原理：

1. JFrame在您致电BufferStrategy时构建createBufferStrategy(2);。 BufferStrategy知道它属于JFrame的特定实例。您正在检索它并将其存储在bs字段中。
2. 当您需要绘制内容时，您正在从Graphics2D检索bs。此Graphics2D对象与bs拥有的内部缓冲区之一相关联。当你画画时，一切都进入那个缓冲区。
3. 当您最终调用bs.show()时，bs将导致您刚刚绘制的缓冲区成为JFrame的当前缓冲区。它知道如何做到这一点，因为（见第1点）它知道它正在服务的JFrame。

这就是所有这一切。

通过对您的代码发表评论......您应该稍微改变您的绘图程序。而不是：

try{
    g2 = (Graphics2D) bs.getDrawGraphics();
    drawWhatEver(g2);
} finally {
       g2.dispose();
}
bs.show();

你应该有这样一个循环：

do {
    try{
        g2 = (Graphics2D) bs.getDrawGraphics();
        drawWhatEver(g2);
    } finally {
           g2.dispose();
    }
    bs.show();
} while (bs.contentsLost());

这可以防止丢失的缓冲帧，根据the docs，偶尔会发生这种情况。