Java swing双缓冲(Java swing double buffering)

我刚开始使用双缓冲，一切正常，直到我想添加一个JScrollPane到屏幕上，所以后来我可以做一些相机移动。一切都很好（我的精灵）除了JScrollPane的ScrollBars之外。我希望他们被展示！

但是，如果我调整窗口大小，滚动条闪烁，所以我知道他们在那里！如果我足够快，我甚至可以使用它们。他们怎么没有出现在渲染？ :(

这是一个问题的SSCCE：

public class BufferStrategyDemo extends JFrame { private BufferStrategy bufferStrategy; private JPanel gameField; private JScrollPane scroll; public BufferStrategyDemo() { this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.getContentPane().setPreferredSize(new Dimension(800, 600)); this.pack(); this.createBufferStrategy(2); this.gameField = new JPanel(); this.gameField.setPreferredSize(new Dimension( 1400, 600 )); this.scroll = new JScrollPane( gameField ); this.add( scroll, BorderLayout.CENTER ); this.setVisible( true ); this.bufferStrategy = this.getBufferStrategy(); setupGameFieldContent(); new Renderer( this, scroll , bufferStrategy ).start(); } // Add some contents to gameField that shows up fine private void setupGameFieldContent() { // For ( all my sprites ) // gameField.add( sprite ); } private class Renderer extends Thread { private BufferStrategy bufferStrategy; private JFrame window; private JScrollPane scroll; private Image imageOfGameField; public Renderer( JFrame window, JScrollPane scroll, BufferStrategy bufferStrategy ) { this.bufferStrategy = bufferStrategy; this.window = window; this.scroll = scroll; } public void run() { while ( true ) { Graphics g = null; try { g = bufferStrategy.getDrawGraphics(); drawSprites(g); } finally { g.dispose(); } bufferStrategy.show(); // Shows everything except the scrollbars.. Toolkit.getDefaultToolkit().sync(); try { Thread.sleep( 1000/60 ) ; } catch(InterruptedException ie) {} } } private void drawSprites( Graphics g ) { Graphics2D g2d=(Graphics2D)g; //Also tried using the JPanels (gameField) createImage with same result imageOfGameField = this.scroll.createImage(800, 600 ); Graphics screen = (Graphics2D)imageOfGameField.getGraphics(); /** * For all my sprites, draw on the image for ( Sprite current : sprites ) screen.drawImage( current.getImage(), current.getX(), current.getY(), current.getWidth() , current.getHeight(), null); */ g2d.drawImage( imageOfGameField, 0, 0 , null ); } } }

i just started using double buffering and everything worked just fine until i wanted to add a JScrollPane to the screen so i later on can do some camera movements. Everything shows up fine (my sprites) EXCEPT the ScrollBars of the JScrollPane. And i want them to be shown!

However if i resize the window, the scrollbars flicker, so i know they are there! I can even use them if i'm fast enough. How come they dont show up at rendering? :(

Here is a SSCCE of the problem:

最满意答案

绘图在整个框架区域上执行，而不是在gameField上gameField 。实际上，临时JScrollPane出现的唯一原因是它会立即调用paintImmediately在鼠标拖动处理程序中的某处。

首先想到的是用Canvas替换JPanel ，就像I_Love_Thinking写道的那样，然后从该canvas实例中获取bufferStategy并将其用于渲染。但不幸的是，它没有按预期工作。轻量级JScrollPane无法正常驱动重量级Canvas 。 Canvas拒绝在区域外绘制内容（0,0，viewport_width，viewport_height）。这是已知的错误，它不会修复。混合重量级组件和轻量级是不好的主意。

用重量级ScrollPane替换JScrollPane似乎ScrollPane 。几乎。在某些情况下，滚动条上会出现明显的渲染瑕疵。

此时，我决定停止跳墙并放弃。滚动窗格是许多问题的来源，不值得用于懒惰滚动。是时候从另一个视图看滚动了。 Canvas 不是游戏领域本身，而是我们用来观察游戏世界的窗口。这是gamedev中众所周知的渲染策略。画布的大小与可观察区域完全相同。当需要滚动时，我们只是用一些偏移量渲染世界。 offset的值可以从某个外部滚动条获取。

我建议下一个改变：

扔掉JScrollPane 将画布直接添加到框架。在画布下添加单个水平JScrollBar 。使用滚动条的值来移动渲染。

该示例基于您的代码。此实现不考虑帧的大小调整。在现实生活中，一些地方需要与视口的大小同步（这是我们之前为之做的scrollpane）。此外，示例违反了Swing线程规则，并从呈现线程读取滚动条的值。

import java.awt.BorderLayout; import java.awt.Canvas; import java.awt.Color; import java.awt.Dimension; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Toolkit; import java.awt.image.BufferStrategy; import java.awt.image.BufferedImage; import javax.swing.JFrame; import javax.swing.JScrollBar; public class BufferStrategyDemo extends JFrame { private BufferStrategy bufferStrategy; private Canvas gameField; private JScrollBar scroll; public BufferStrategyDemo() { setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); getContentPane().setLayout(new BorderLayout()); getContentPane().setPreferredSize(new Dimension(800, 600)); gameField = new Canvas(); gameField.setIgnoreRepaint(true); gameField.setPreferredSize(new Dimension(800, 580)); getContentPane().add(gameField, BorderLayout.CENTER); scroll = new JScrollBar(JScrollBar.HORIZONTAL); scroll.setPreferredSize(new Dimension(800, 20)); scroll.setMaximum(1400 - 800); // image width - viewport width getContentPane().add(scroll, BorderLayout.SOUTH); this.pack(); gameField.createBufferStrategy(2); bufferStrategy = gameField.getBufferStrategy(); new Renderer().start(); } private class Renderer extends Thread { private BufferedImage imageOfGameField; public Renderer() { // NOTE: image size is fixed now, but better to bind image size to the size of viewport imageOfGameField = new BufferedImage(1400, 580, BufferedImage.TYPE_INT_ARGB); } public void run() { while (true) { Graphics g = null; try { g = bufferStrategy.getDrawGraphics(); drawSprites(g); } finally { g.dispose(); } bufferStrategy.show(); Toolkit.getDefaultToolkit().sync(); try { Thread.sleep(1000 / 60); } catch (InterruptedException ie) { } } } private void drawSprites(Graphics g) { Graphics2D g2d = (Graphics2D) g; Graphics g2d2 = imageOfGameField.createGraphics(); g2d2.setColor(Color.YELLOW); // clear background g2d2.fillRect(0, 0, 1400, 580); // again, fixed width/height only for SSCCE g2d2.setColor(Color.BLACK); int shift = -scroll.getValue(); // here it is - get shift value g2d2.fillRect(100 + shift, 100, 20, 20); // i am ugly black sprite g2d2.fillRect(900 + shift, 100, 20, 20); // i am other black sprite // located outside of default view g2d.drawImage(imageOfGameField, 0, 0, null); g2d2.dispose(); } } public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { public void run() { BufferStrategyDemo mf = new BufferStrategyDemo(); mf.setVisible(true); } }); } }

另一个例子，主要基于来自Java游戏的代码：主动渲染文章。它与JScrollBar值和Canvas大小正确同步。此外，它直接绘制到Graphics ，从BufferStrategy实例中获取（而不是中间的BuffereImage对象）。结果是这样的：

主动渲染演示

Drawing is performed on whole frame area, not on gameField. Actually, the only cause of temporary JScrollPane appearing is that it calls paintImmediately somewhere in mouse-drag handler.

The first thing that comes to mind is to replace JPanel with Canvas, as I_Love_Thinking wrote, then get bufferStategy from that canvas instance and use it for rendering. But unfortunately it not works as expected. Lightweight JScrollPane can't properly drive heavyweight Canvas. Canvas refuses to draw content outside area (0, 0, viewport_width, viewport_height). This is known bug and it will not fixed. Mixing mixing heavyweight components with lightweight is bad idea.

Replacing JScrollPane with heavyweight ScrollPane seems working. Almost. There are noticeable rendering artifacts on scroll bars under some circumstances.

At this point, I've decided to stop beating the wall and give up. Scroll panes are the source of numerous problems and not worth to use for lazy scrolling. It is time to look on scrolling from another view. The Canvas is not game field itself, but window that we use to observe game world. This is well-known rendering strategy in gamedev. The size of canvas is exactly as observable area. When scrolling needed, we just render the world with some offset. The value for offset may be taken from some external scrollbar.

I suggest next changes:

Throw away JScrollPane Add canvas directly to frame. Add single horizontal JScrollBar under canvas. Use value of scrollbar to shift rendering.

The example is based on your code. This implementation not respects resizing of frame. In real life some places need to be synchronized with size of viewport (that what scrollpane did before for us). Also, example violates Swing threading rules and reads value of scrollbar from rendering thread.

And another example, mostly based on code from Java Games: Active Rendering article. It properly synchronized with value of JScrollBar and size of Canvas. Also, it does painting directly to Graphics, obtained from BufferStrategy instance (instead of intermediate BuffereImage object). The result is something like this:

Active Rendering Demo

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