Java Swing：drawLine非常慢

Question

我正在寫一個使用swing的java應用程序，其中我需要在正方形上方繪製網格。爲此，我使用Graphics類提供的drawLine(...)方法。

一切工作正常，但它需要大量的時間繪製每一行（超過20秒50行...）。我甚至可以看到實時繪製的線條。奇怪的是，水平線的繪製方式比垂直線快（幾乎立即）。

我可能會做錯事。這是網格的代碼。

public void drawGrid(Graphics g){ 
    g.setColor(new Color(255, 255, 255, 20)); 
    int width = getWidth(); 
    int height = (int) (width * Utils.PLATE_RATIO); 
    int step = pixelSize*gridSpacing; 
    Color bright = new Color(255, 255, 255, 100); 
    Color transparent = new Color(255, 255, 255, 20); 
    for(int ix = insets.left + step;       
      ix < width; ix += step){ 
     if(((ix - insets.left)/step) % 10 == 0){ 
      g.setColor(bright); 
     } 
     else{ 
      g.setColor(transparent); 
     } 
     g.drawLine(ix, insets.top, ix, height+insets.top); 
    } 
    for(int iy = insets.top+step; 
      iy < (insets.top + height); iy += step){ 
     if(((iy - insets.top)/step) % 10 == 0){ 
      g.setColor(bright); 
     } 
     else{ 
      g.setColor(transparent); 
     } 
     g.drawLine(insets.left, iy, width + insets.left, iy); 
    } 
} 

Answer 1

您發佈的代碼很好，沒有問題。
下面是使用的方法（有點簡化）的部件的一個工作示例：

public static class MyGrid extends JComponent 
{ 
    private int step = 10; 

    public MyGrid() 
    { 
     super(); 
    } 

    public Dimension getPreferredSize() 
    { 
     return new Dimension (500, 500); 
    } 

    protected void paintComponent (Graphics g) 
    { 
     super.paintComponent (g); 
     drawGrid (g); 
    } 

    public void drawGrid (Graphics g) 
    { 
     int width = getWidth(); 
     int height = getHeight(); 
     Color bright = new Color (255, 255, 255, 200); 
     Color transparent = new Color (255, 255, 255, 100); 

     for (int ix = step; ix < width; ix += step) 
     { 
      if ((ix/step) % 10 == 0) 
      { 
       g.setColor (bright); 
      } 
      else 
      { 
       g.setColor (transparent); 
      } 
      g.drawLine (ix, 0, ix, height); 
     } 

     for (int iy = step; iy < height; iy += step) 
     { 
      if ((iy/step) % 10 == 0) 
      { 
       g.setColor (bright); 
      } 
      else 
      { 
       g.setColor (transparent); 
      } 
      g.drawLine (0, iy, width, iy); 
     } 
    } 
} 

我想有那一段代碼之外的一些問題。

P.S.有點偏移，但...

我建議你計算繪畫區域的可見部分（使用JComponent的getVisibleRect()方法或圖形g.getClip().getBounds()方法），並限制你的繪畫只有該區域。

如果組件面積很大（例如10000x10000像素組件的面積），那麼這個小的優化可能會加快組件的繪製速度。

Answer 2

這是我如何使用雙緩衝來解決問題，正如@sureshKumar所建議的那樣。我只是畫一幅離屏圖像，並在繪圖結束時簡單地調用drawImage()。這似乎有伎倆。

編輯：這似乎只是如果你想打電話給你的繪畫方法（在我的情況drawGrid()）從paintComponent(...)方法之外是有用的。

下面是代碼：

private Graphics bufferGraphics; 
private Image offScreen; 
private Dimension dim; 
//other attributes not shown... 

public CentralPanel(){ 
    //Some initialization... (not shown) 

    //I added this listener so that the size of my rectangle 
    //and of my grid changes with the frame size 
    this.addComponentListener(new ComponentListener() { 

     @Override 
     public void componentResized(ComponentEvent e) { 
      dim = getVisibleRect().getSize(); 
      offScreen = createImage(dim.width, dim.height); 
      bufferGraphics = offScreen.getGraphics(); 
      repaint(); 
      revalidate(); 
     } 
     //other methods of ComponentListener not shown 
    }); 
} 

@Override 
protected void paintComponent(Graphics g) { 
    super.paintComponent(g); 
    g.drawImage(offScreen, 0, 0, null); 
} 

public void drawGrid(){ 
    int width = dim.width - insets.left - insets.right; 
    width -= (width % plateSize.getXSize()); 
    int height = (int) (width*Utils.PLATE_RATIO); 
    height -= (height % plateSize.getYSize()); 
    int step = pixelSize*gridSpacing; 
    Color bright = new Color(255, 255, 255, 100); 
    Color transparent = new Color(255, 255, 255, 20); 
    for(int ix = insets.left + step;       
      ix < (width+insets.left); ix += step){ 
     if(((ix - insets.left)/step) % 10 == 0){ 
      bufferGraphics.setColor(bright); 
     } 
     else{ 
      bufferGraphics.setColor(transparent); 
     } 
     //I am now drawing on bufferGraphics instead 
     //of the component Graphics 
     bufferGraphics.drawLine(ix, insets.top, ix, height+insets.top); 
    } 
    step *= Utils.PLATE_RATIO; 
    for(int iy = insets.top+step; 
      iy < (insets.top + height); iy += step){ 
     if(((iy - insets.top)/step) % 10 == 0){ 
      bufferGraphics.setColor(bright); 
     } 
     else{ 
      bufferGraphics.setColor(transparent); 
     } 
     bufferGraphics.drawLine(insets.left, iy, width + insets.left, iy); 
    } 
} 

P.S：如果這應該作爲一個編輯我的問題，請告訴我，我會做到這一點。