Question

我正试图利用摩擦听众创建一种末级工具:

public void mouseDragged(MouseEvent e) {
            imageL.setCoordinates(originalPos, e.getPoint());
            imageL.repaint();
            originalPos = e.getPoint();
        }

JLabel(imageL)的油漆功能有两套点,可以根据 mo泥提取一条线。唯一的问题是,每当拖拉时,新一层并不包含从以前的暴动中提取的线。 JLabel的油漆功能如下:

public void paint(Graphics g) {
    super.paint(g); 
    Graphics2D g2d = (Graphics2D)g;
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.setColor(drawingColour);
    g2d.drawLine(originCors.x,originCors.y,endCors.x,endCors.y);
}

因此,基本上我的问题是:我如何“把新线带给目前的层?

any help would be great, Thanks in advance

Answer 1

You want to draw in a JComponent s (and JLabel extends from JComponent) paintComponent method, not the paint method unless you plan to handle all the painting of the component s borders and children. Next, you may wish to have your drawing component hold an ArrayList of Point and add Points to this array list in the mouseDragged method. Then the paintComponent method can iterate through the list and paint all the lines. If all you want to do is paint one line, then have the painting JLabel hold both points in a class field.

Answer 2

Michael,

从一开始,在缝wing中(JLabel是一个周转部分,与旧的AWT图书馆相联),所建议的做法是超越<代码>paintComponent(而不是“paint”方法)。见。 The Java Tutorials: Hyphaing for the hows & whys of it.

If you want to custom-paint a-list-of-lines then you re going to have to do just that... not just the "new" one. One way around this is to "update" an image with each new line, and then custom-paint that... this is slightly quicker as you only "paint" the each line once, at the cost of using more memory (to maintain the "backgroun image")... but this technique lends itself to "double buffering", which avoids "that flickering" you get when you draw directly to the screen. See The Java Tutorials: Working with Images for the details. It s actually pretty straight forward.

I suggest you google for "java double buffering example" (avoid Rose India, it s full of crap).

Cheers. Keith.

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