即使使用Java Swing超过一年，它对我来说仍然是神奇的。我如何正确使用BufferStrategy，特别是方法createBufferSrategy()？
我想要一个JFrame和一个Canvas，它被添加到它然后绘制。我还希望能够调整画布（setSize()）的大小。每当我调整画布大小时，似乎我的BufferStrategy被删除，或者更确切地说，变得无用，因为在show()上使用BufferStrategy实际上并没有做任何事情。此外，createBufferStrategy()有一个奇怪的非确定性行为，我不知道如何正确地同步它。
这就是我的意思：
public class MyFrame extends JFrame {
MyCanvas canvas;
int i = 0;
public MyFrame() {
setUndecorated(false);
setVisible(true);
setSize(1100, 800);
setLocation(100, 100);
setDefaultCloseOperation(EXIT_ON_CLOSE);
canvas = new MyCanvas();
add(canvas);
canvas.makeBufferStrat();
}
@Override
public void repaint() {
super.repaint();
canvas.repaint();
//the bigger threshold's value, the more likely it is that the BufferStrategy works correctly
int threshold = 2;
if (i < threshold) {
i++;
canvas.makeBufferStrat();
}
}
}
MyCanvas有一个方法makeBufferStrat()和repaint()：
public class MyCanvas extends Canvas {
BufferStrategy bufferStrat;
Graphics2D g;
public MyCanvas() {
setSize(800, 600);
setVisible(true);
}
public void makeBufferStrat() {
createBufferStrategy(2);
//I'm not even sure whether I need to dispose() those two.
if (g != null) {
g.dispose();
}
if (bufferStrat != null) {
bufferStrat.dispose();
}
bufferStrat = getBufferStrategy();
g = (Graphics2D) (bufferStrat.getDrawGraphics());
g.setColor(Color.BLUE);
}
@Override
public void repaint() {
g.fillRect(0, 0, 100, 100);
bufferStrat.show();
}
}
我只是在main方法中的while（true）循环中调用MyFrame的{{1}}方法。
当repaint()很小（即2）时，大约70％的情况下threshold都没有做任何事情 - JFrame在启动程序时仍然是灰色的。剩余的30％它绘制了矩形它应该如何。如果我做bufferStrat.show()，那么在我执行程序时，绘画成功接近100％。 Javadoc说threshold = 200;可能需要一段时间，所以我认为这是问题所在。但是，如何正确同步和使用它？显然，我在这里做错了。我无法想象它应该如何被使用。
有没有人有一个最小的工作示例？
答案 0 :(得分：2)
您创建BufferStrategy的方式是“好的”，您可以查看JavaDocs for BufferStrategy，它有一个简洁的小例子。
你使用它的方式是值得怀疑的。使用BufferStrategy的主要原因是因为你想要控制绘画过程（主动绘画）远离Swing的绘画算法（这是被动的）
但是，你似乎试图做到这两点，这就是为什么它会导致你的问题。相反，你应该有一个“主”循环，负责决定缓冲区应该绘制的内容和时间，例如......
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferStrategy;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Test {
public static void main(String[] args) {
new Test();
}
public Test() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
TestPane testPane = new TestPane();
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(testPane);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
// The component needs to be attached to displayed window before
// the buffer can be created
testPane.startPainting();
}
});
}
public class TestPane extends Canvas {
private AtomicBoolean painting = new AtomicBoolean(true);
private PaintCycle paintCycle;
private Rectangle clickBounds;
public TestPane() {
addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent e) {
if (clickBounds != null && clickBounds.contains(e.getPoint())) {
painting.set(false);
}
}
});
}
public void startPainting() {
if (paintCycle == null) {
createBufferStrategy(2);
painting.set(true);
paintCycle = new PaintCycle();
Thread t = new Thread(paintCycle);
t.setDaemon(true);
t.start();
}
}
public void stopPainting() {
if (paintCycle != null) {
painting.set(false);
}
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
public class PaintCycle implements Runnable {
private BufferStrategy strategy;
private int xDelta = 2;
private int yDelta = 2;
@Override
public void run() {
System.out.println("Painting has started");
int x = (int) (Math.random() * (getWidth() - 40));
int y = (int) (Math.random() * (getHeight() - 40));
do {
xDelta = (int) (Math.random() * 8) - 4;
} while (xDelta == 0);
do {
yDelta = (int) (Math.random() * 8) - 4;
} while (yDelta == 0);
clickBounds = new Rectangle(x, y, 40, 40);
strategy = getBufferStrategy();
while (painting.get()) {
// Update the state of the model...
update();
// Paint the state of the model...
paint();
try {
// What ever calculations you want to use to maintain the framerate...
Thread.sleep(40);
} catch (InterruptedException ex) {
}
}
System.out.println("Painting has stopped");
}
protected void update() {
int x = clickBounds.x + xDelta;
int y = clickBounds.y + yDelta;
if (x + 40 > getWidth()) {
x = getWidth() - 40;
xDelta *= -1;
} else if (x < 0) {
x = 0;
xDelta *= -1;
}
if (y + 40 > getHeight()) {
y = getHeight() - 40;
yDelta *= -1;
} else if (y < 0) {
y = 0;
yDelta *= -1;
}
clickBounds.setLocation(x, y);
}
protected void paint() {
// Render single frame
do {
// The following loop ensures that the contents of the drawing buffer
// are consistent in case the underlying surface was recreated
do {
// Get a new graphics context every time through the loop
// to make sure the strategy is validated
Graphics2D graphics = (Graphics2D) strategy.getDrawGraphics();
// Render to graphics
// ...
graphics.setColor(Color.BLUE);
graphics.fillRect(0, 0, getWidth(), getHeight());
graphics.setColor(Color.RED);
graphics.fill(clickBounds);
// Dispose the graphics
graphics.dispose();
// Repeat the rendering if the drawing buffer contents
// were restored
} while (strategy.contentsRestored());
// Display the buffer
strategy.show();
// Repeat the rendering if the drawing buffer was lost
} while (strategy.contentsLost());
}
}
}
}
您还应该记住，Swing一直使用DirectX或OpenGL管道，因为大约1.4（或1.5）。使用BufferStrategy的主要原因是更直接访问硬件（Swing非常接近）和直接控制绘制过程（现在这是使用它的唯一原因）