鼠标拖动和绘制

Question

我有显示所有三角形的问题。我用鼠标拖动画一个三角形。每次我画一个新的三角形，前一个三角形消失。我怎样才能让三角形留下来，所以绘图面板上会有很多三角形？

..... 
private class PaintSurface extends JComponent { 
    Point startDrag, endDrag, midPoint; 
    Polygon triangle; 
    public PaintSurface() { 
     this.addMouseListener(new MouseAdapter() { 
     public void mousePressed(MouseEvent e) { 
     startDrag = new Point(e.getX(), e.getY()); 
     endDrag = startDrag; 
     repaint(); 
     } 

     public void mouseReleased(MouseEvent e) { 
     Shape r = makeRectangle(startDrag.x, startDrag.y, e.getX(), e.getY());   
     shapes.add(r); 
     if (startDrag.x > endDrag.x) 
      midPoint = new Point((endDrag.x +(Math.abs(startDrag.x - endDrag.x)/2)),e.getY()); 
     else 
      midPoint = new Point((endDrag.x -(Math.abs(startDrag.x - endDrag.x)/2)),e.getY()); 
     int[] xs = { startDrag.x, endDrag.x, midPoint.x }; 
     int[] ys = { startDrag.y, startDrag.y, midPoint.y };   
     triangle = new Polygon(xs, ys, 3);    
     startDrag = null; 
     endDrag = null; 
     repaint(); 
     } 
    }); 

    this.addMouseMotionListener(new MouseMotionAdapter() { 
     public void mouseDragged(MouseEvent e) { 
      endDrag = new Point(e.getX(), e.getY()); 
      repaint(); 
     } 
    }); 
    } 

    public void paint(Graphics g) { 
    Graphics2D g2 = (Graphics2D) g; 
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); 
    paintBackground(g2); 
    Color[] colors = { Color.YELLOW, Color.MAGENTA, Color.CYAN , Color.RED, Color.BLUE, Color.PINK}; 
    int colorIndex = 0; 
    g2.setStroke(new BasicStroke(1)); 
    g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.50f)); 
    g2.fillPolygon(triangle);   
    } 
} 

Answer 1

你在屏幕上看到的是你在绘画功能中绘制的东西。目前，您只能在三角形变量中存储一个三角形，并不断更换和绘制它。

你需要的是存储一个三角形列表，并且每次添加一个新的到mouseReleased的列表。这里是要改变什么：

private class PaintSurface extends JComponent { 
    ... 
    //Polygon triangle; 
    List<Polygon> triangles = new LinkedList<Polygon>(); 
    ... 

    public PaintSurface() { 

     public void mouseReleased(MouseEvent e) { 
     ... 
     //triangle = new Polygon(xs, ys, 3); 
     triangles.add(new Polygon(xs, ys, 3);); 
     ... 
     } 
    }); 
    ... 
    } 

    public void paint(Graphics g) { 
    ... 
    //g2.fillPolygon(triangle); 
    for (Polygon triangle : triangles) g2.fillPolygon(triangle); 
    ... 
    } 
} 

Answer 2

Polygon triangle; 

你到总计一个三角形对象的引用，所以每次重绘画布时，你会得出这样的一个多边形。

一对夫妇的解决方案：

• 创建Polygon对象的列表，并吸引他们所有当paint被调用。您的鼠标侦听器会向列表中添加一个新条目。
• 将您的多边形绘制到BufferedImage上，然后在绘制方法中使用draw the image。如果你计划绘制许多三角形，这可能是更好的选择。

Answer 3

不是很奇怪。您有一个三角形对象，只要您开始画一个新的三角形，就会覆盖它。

创建一个三角形的数组/列表，并让绘图例程绘制该图形。

我的Java修改：

..... 
    private class PaintSurface extends JComponent { 
    Point startDrag, endDrag, midPoint; 
    List triangles = new ArrayList(); 
    public PaintSurface() { 
     this.addMouseListener(new MouseAdapter() { 
     public void mousePressed(MouseEvent e) { 
      startDrag = new Point(e.getX(), e.getY()); 
      endDrag = startDrag; 
      repaint(); 
    } 

    public void mouseReleased(MouseEvent e) { 
    Shape r = makeRectangle(startDrag.x, startDrag.y, e.getX(), e.getY());   
    shapes.add(r); 
    if (startDrag.x > endDrag.x) 
     midPoint = new Point((endDrag.x +(Math.abs(startDrag.x - endDrag.x)/2)),e.getY()); 
    else 
     midPoint = new Point((endDrag.x -(Math.abs(startDrag.x - endDrag.x)/2)),e.getY()); 
    int[] xs = { startDrag.x, endDrag.x, midPoint.x }; 
    int[] ys = { startDrag.y, startDrag.y, midPoint.y };   
    Polygon triangle = new Polygon(xs, ys, 3);    
    traingles.add(triangle); 
    startDrag = null; 
    endDrag = null; 
    repaint(); 
    } 
}); 

this.addMouseMotionListener(new MouseMotionAdapter() { 
    public void mouseDragged(MouseEvent e) { 
     endDrag = new Point(e.getX(), e.getY()); 
     repaint(); 
    } 
}); 
    } 

    public void paint(Graphics g) { 
     Graphics2D g2 = (Graphics2D) g; 
     g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); 
     paintBackground(g2); 
     Color[] colors = { Color.YELLOW, Color.MAGENTA, Color.CYAN , Color.RED, Color.BLUE, Color.PINK}; 
     int colorIndex = 0; 
     g2.setStroke(new BasicStroke(1)); 
     g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.50f)); 
     Iterator iter = triangles.iterator(); 
     while(iter.hasNext()) { 
      g2.fillPolygon((Polygon)iter.next());   
     } 
    } 
    }