java - 通过拖动绘制形状

Question

我是图形编程的新手。我想通过拖动鼠标来绘制多种形状，例如直线、矩形和椭圆形。我尝试完成这项任务但失败了。

我的输出看起来像这样。

这是我的代码:

public class JavaDraw extends JPanel implements ActionListener,
    MouseMotionListener, MouseListener {

private JButton btnLine, btnRect, btnEclipse, btnPointer;
private DrawShape drawShape;
private Vector<Line2D.Double> vecLine;
private Vector<Rectangle2D.Double> vecRectangle;
private Vector<Ellipse2D.Double> vecEllipse;
private int left, right, top, bottom;
private Point startPoint, endPoint;

public JavaDraw(int width, int height) {
    this();
    setSize(width, height);
    setBackground(Color.orange);
}

public JavaDraw() {

    setLayout(new FlowLayout(FlowLayout.CENTER));

    createControl();
    addControl();
    addListners();
}

private void createControl() {
    btnEclipse = new JButton("Eclipse");
    btnLine = new JButton("Line");
    btnRect = new JButton("Rectangle");
    btnPointer = new JButton("Pointer");

    vecEllipse = new Vector<>();
    vecLine = new Vector<>();
    vecRectangle = new Vector<>();

    startPoint = new Point();
    endPoint = new Point();
}

private void addControl() {

    add(btnLine);
    add(btnRect);
    add(btnEclipse);
    add(btnPointer);
}

private void addListners() {
    addActionListenerToControl();
    addMouseListenerToControl();
    addMouseMotionListenerToControl();
}

private void addActionListenerToControl() {
    btnEclipse.addActionListener(this);
    btnLine.addActionListener(this);
    btnPointer.addActionListener(this);
    btnRect.addActionListener(this);
}

private void addMouseListenerToControl() {
    addMouseListener(this);
}

private void addMouseMotionListenerToControl() {
    addMouseMotionListener(this);
}

private void resizeShape(int x, int y) {
    endPoint.x = x;
    endPoint.y = y;
    updateBounds(startPoint, endPoint);
}

private void drawShape(Graphics g, boolean xor, DrawShape dm) {

    if (drawShape == DrawShape.DRAW_RECT)
        g.drawRect(left, top, Math.abs(left - right),
                Math.abs(top - bottom));
    else if (drawShape == DrawShape.DRAW_ELLIPSE)
        g.drawOval(left, top, Math.abs(left - right),
                Math.abs(top - bottom));
    else if (drawShape == DrawShape.DRAW_LINE)
        g.drawLine(startPoint.x, startPoint.y, endPoint.x, endPoint.y);
}

void updateBounds(Point pt1, Point pt2) {
    left = (pt1.x < pt2.x) ? pt1.x : pt2.x;
    right = (pt1.x > pt2.x) ? pt1.x : pt2.x;
    top = (pt1.y < pt2.y) ? pt1.y : pt2.y;
    bottom = (pt1.y > pt2.y) ? pt1.y : pt2.y;
}

@Override
public void actionPerformed(ActionEvent e) {
    Graphics g = getGraphics();
    g.setColor(Color.black);
    g.setXORMode(getBackground());

    if (e.getSource() == btnEclipse) {
        drawShape = DrawShape.DRAW_ELLIPSE;
    } else if (e.getSource() == btnLine) {
        drawShape = DrawShape.DRAW_LINE;
    } else if (e.getSource() == btnRect) {
        drawShape = DrawShape.DRAW_RECT;
    } 
    g.setPaintMode();
}

@Override
public void mouseDragged(MouseEvent e) {
    Graphics g = getGraphics();
    g.setColor(Color.black);
    g.setXORMode(getBackground());

    resizeShape(e.getX(), e.getY());
    drawShape(g, true, drawShape);

}

@Override
public void mouseMoved(MouseEvent e) {
}

@Override
public void mouseClicked(MouseEvent e) {
}

@Override
public void mouseEntered(MouseEvent e) {
}

@Override
public void mouseExited(MouseEvent e) {
}

@Override
public void mousePressed(MouseEvent e) {
    startPoint = e.getPoint();
}

@Override
public void mouseReleased(MouseEvent e) {
}

}

enum DrawShape {
    DRAW_LINE, DRAW_RECT, DRAW_ELLIPSE
}

但是如果我调用repaint()方法，那么之前绘制的形状就会消失。

请帮我解决。

提前致谢。

Answer 1

不要使用getGrapchic() 。您需要学习定制绘画的基础知识。请参阅Performing Custom Painting 。基本上你想要做的是覆盖 paintComponent并在那里画画。

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

当你 repaint()面板，paintComponent将被隐式调用。所以你可以做类似的事情

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    for (Rectangle2D rect: rectangles) {
        g2.fill(rect);
    }
}

例如，您可以添加新的 Rectangle2D反对List<Rectangle2D> rectagles ，并且 Canvas 上会绘制另一个矩形。

您可能还想查看this answer ，它展示了如何通过拖动鼠标来创建形状

示例中的代码仅使用一个矩形，但您可以轻松修改它以绘制 List的矩形。每次按下鼠标时，它都会向列表中添加一个新矩形，同时仍然允许您拖动鼠标来调整通过鼠标按下获得的当前矩形的大小。检查链接。希望对您有所帮助。