repaint（）的繪製速度比paintComponent（）慢嗎？

Question

我正在繪製使用paintComponent（）定義的車輛對象。 由於車輛可以移動，我實現了ActionListener並設置了一個Timer（）來觸發。

因此，我的車輛可以移動。但它有點「動搖」。當我不斷調整窗口大小來調用paintComponent（）時，運動變得平滑。當我不調整窗口大小（不調用paintComponent）時，它會再次出現黑屏。爲什麼？如何解決它？

public class VehiclesComponent extends JComponent implements ActionListener{ 
    private Vehicle[] vehicles; 
    private Timer timer; 

    public VehiclesComponent(int n){ 
     vehicles = Vehicle.generateVehicle(n); 
     timer = new Timer(5,this); 
    } 

    public void paintComponent(Graphics g){ 
     super.paintComponent(g); 
     Graphics2D g2 = (Graphics2D)g; 

     for (int i=0; i<vehicles.length; i++) { 
      vehicles[i].draw(g2); 
     } 

     // may change later 
     timer.start(); 
    } 

    @Override 
    public void actionPerformed(ActionEvent e){ 

     //check collision in here 
     for (Vehicle v : vehicles) { 
      if (Vehicle.intersectsOther(v, vehicles)) { 
       v.collisionSideEffect(); 
      } 
     } 

     //move all in here 

     for (Vehicle v : vehicles) { 
      v.move(); 
     } 

     repaint(); 
     //?? repaint slower than paintComponent 
    } 


} 

Answer 1

首先看看Painting in AWT and Swing。請記住，repaint只是對RepaintManager的建議，RepaintManager可能會選擇將多個repaint調用合併爲較少數量的實際繪畫事件。

確保你打電話給super.paintComponent，否則你將最終沒有奇怪的油漆文物結束。

不要，直接或間接地修改組件或從任何油漆方法內螞蟻其它組件的狀態，這將導致一個新repaint請求而做出的，這可能導致油漆事件的循環可能消耗你的CPU週期。這意味着，請不要撥打timer.start()！

沒有一個可運行的例子，我一起蹣跚而行。現在，這是動畫10，000個人Vehicle S（矩形），所以它在大量殺死，但它應該提供的點...

（GIF將只在運行7FPS，而不是你200fps）

import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.Rectangle; 
import java.awt.Shape; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import javax.swing.JComponent; 
import javax.swing.JFrame; 
import javax.swing.Timer; 
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(); 
       } 

       JFrame frame = new JFrame("Testing"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       frame.add(new VehiclesComponent(10000)); 
       frame.pack(); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 

    public class VehiclesComponent extends JComponent implements ActionListener { 

     private Vehicle[] vehicles; 
     private Timer timer; 

     public VehiclesComponent(int n) { 
      vehicles = Vehicle.generateVehicle(n, getPreferredSize()); 
      timer = new Timer(5, this); 

      timer.start(); 
     } 

     @Override 
     public Dimension getPreferredSize() { 
      return new Dimension(400, 400); 
     } 

     @Override 
     protected void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      Graphics2D g2 = (Graphics2D) g; 

      for (int i = 0; i < vehicles.length; i++) { 
       vehicles[i].draw(g2); 
      } 
     } 

     @Override 
     public void actionPerformed(ActionEvent e) { 

      //check collision in here 
//   for (Vehicle v : vehicles) { 
//    if (Vehicle.intersectsOther(v, vehicles)) { 
//     v.collisionSideEffect(); 
//    } 
//   } 

     //move all in here 
      for (Vehicle v : vehicles) { 
       v.move(this.getSize()); 
      } 

      repaint(); 
      //?? repaint slower than paintComponent 
     } 

    } 

    public static class Vehicle { 

     protected static final int SIZE = 5; 
     protected static final Color[] COLORS = new Color[]{ 
      Color.BLACK, 
      Color.BLUE, 
      Color.CYAN, 
      Color.DARK_GRAY, 
      Color.GREEN, 
      Color.MAGENTA, 
      Color.ORANGE, 
      Color.PINK, 
      Color.RED, 
      Color.WHITE, 
      Color.YELLOW 
     }; 

     private int x = 0; 
     private int y = 0; 

     private int xDelta; 
     private int yDelta; 

     private Shape car; 
     private Color color; 

     public static Vehicle[] generateVehicle(int count, Dimension bounds) { 

      Vehicle[] vehicles = new Vehicle[count]; 
      for (int index = 0; index < vehicles.length; index++) { 
       vehicles[index] = new Vehicle(bounds); 
      } 

      return vehicles; 

     } 

     public Vehicle(Dimension size) { 

      x = (int)(Math.random() * (size.width - SIZE)); 
      y = (int)(Math.random() * (size.height - SIZE)); 

      xDelta = (int)(Math.random() * 3) + 1; 
      yDelta = (int)(Math.random() * 3) + 1; 
      car = new Rectangle(SIZE, SIZE); 

      color = COLORS[(int)(Math.random() * COLORS.length)]; 

     } 

     public void move(Dimension size) { 
      x += xDelta; 
      y += yDelta; 

      if (x < 0) { 
       x = 0; 
       xDelta *= -1; 
      } else if (x + SIZE > size.width) { 
       x = size.width - SIZE; 
       xDelta *= -1; 
      } 
      if (y < 0) { 
       y = 0; 
       yDelta *= -1; 
      } else if (y + SIZE > size.height) { 
       y = size.height - SIZE; 
       yDelta *= -1; 
      } 

     } 

     public void draw(Graphics2D g2) { 
      g2.translate(x, y); 
      g2.setColor(color); 
      g2.fill(car); 
      g2.translate(-x, -y); 
     } 

    } 

} 

你也可以看看this example這使得在任意方向4500幅圖像的向上和演示了一些優化技術。

也可以看看this example，其能夠在兩個方向和旋轉動畫的，向上的10，000圖像