java 了解缓冲策略

Understand BufferStrategy

提问by Charlie Villy

I'm kind of new to java. I want to make a game. After a lot of research, I can't understand how bufferstrategy works.. I know the basics.. it creates an off-screen image that you can later put into your windows object.. I got this

我对java有点陌生。我想做一个游戏。经过大量研究，我无法理解 bufferstrategy 的工作原理.. 我知道基础知识.. 它创建了一个离屏图像，您可以稍后将其放入您的 windows 对象中.. 我明白了

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..
   }
  }

I don't know.. I've been studying this for a long time now.. and with no luck at all.. I don't know.. maybe it's all there, and it's really clear and simple, and I'm just too stupid to see it..

我不知道.. 我已经研究了很长时间了.. 一点运气都没有.. 我不知道.. 也许一切都在那里，而且非常清晰和简单，而且我'我只是太笨了看不到它..

Thanks for all the help.. :)

感谢所有的帮助.. :)

回答by Ted Hopp

Here's how it works:

这是它的工作原理：

1. The JFrameconstructs a BufferStrategywhen you call createBufferStrategy(2);. The BufferStrategyknows that it belongs to that specific instance of JFrame. You are retrieving it and storing it in the bsfield.
2. When it comes time to draw your stuff, you are retrieving a Graphics2Dfrom bs. This Graphics2Dobject is tied to one of the internal buffers owned by bs. As you draw, everything goes into that buffer.
3. When you finally call bs.show(), bswill cause the buffer that you just drew to become the current buffer for the JFrame. It knows how to do this because (see point 1) it knows what JFrameit is in service to.

1. 该JFrame构造了一个BufferStrategy当你调用createBufferStrategy(2);。TheBufferStrategy知道它属于JFrame. 您正在检索它并将其存储在bs现场。
2. 当需要绘制你的东西时，你正在Graphics2D从bs. 此Graphics2D对象绑定到 拥有的内部缓冲区之一bs。当你画画时，一切都会进入那个缓冲区。
3. 当您最终调用 时bs.show()，bs将导致您刚刚绘制的缓冲区成为 的当前缓冲区JFrame。它知道如何做到这一点，因为（参见第 1 点）它知道它的用途JFrame。

That's all that's going on.

这就是正在发生的一切。

By way of comment to your code...you should change your drawing routine a bit. Instead of this:

通过对您的代码进行评论的方式...您应该稍微更改您的绘图程序。取而代之的是：

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

you should have a loop like this:

你应该有一个这样的循环：

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

That will safeguard against lost buffer frames, which, according to the docs, can happen occasionally.

这将防止丢失缓冲区帧，根据文档，这种情况偶尔会发生。