java - 自定义绘画代码无法正确更新，我尝试尊重剪辑区域。运行一下看看

Question

这是可运行的java代码。如果您想测试它，请复制下面的两个代码摘录。编译并运行Triangleframe.java

我正在 JPanel 上绘制两个三角形(可能稍后我会添加更多)。我点击三角形之一并将其拖动。在我决定遵循 Oracle 在本课中推荐的剪辑区域之前，这曾经(在某种程度上)有效: Custom painting

我从 repaint() 切换到 repaint(x,y,with,height) 的原因是，当我尝试拖动其中一个三角形时，它是重新绘制非常缓慢，而且它也不太擅长跟随鼠标指针(滞后？)。我推断，保持在界限内并仅重新绘制我正在使用的屏幕部分可以解决问题。它确实修复了延迟，但现在只要按下鼠标按钮，我正在重新绘制的边界框似乎就不会移动。三角形仅在边界框内移动。直到我释放鼠标按钮(此时创建了一个新三角形)。最好我应该只重画三角形而不是边界框，但为了方便起见，我尝试首先解决这个问题。希望三角形能够重叠。

请参阅代码中的注释以获取更深入的解释。

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.Rectangle; 
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.JPanel;

//********************************************************************
//*** This is a stripped down version of the code which shows      ***
//*** the problem. Just create an instance of the class by running *** 
//*** TriangleFrame.java. Then try to drag either triangle with    ***
//*** the mouse.                                                   ***
//********************************************************************
public class TrianglePanel extends JPanel implements MouseListener,
    MouseMotionListener {

    Triangle triangle1 = null;
    Triangle triangle2 = null;
    Rectangle boundingBox = null;

    int lastXPos = 0;
    int lastYPos = 0;
    boolean draggable = false;

    public TrianglePanel() {

        triangle1 = new Triangle(new Point(100, 10), new Point(50, 100),
                new Point(150, 100));
        triangle2 = new Triangle(new Point(250, 10), new Point(150, 100),
                new Point(350, 100));
        lastXPos = this.getX();
        lastYPos = this.getY();

        addMouseListener(this);
        addMouseMotionListener(this);
    }

    @Override
    public void mouseReleased(MouseEvent e) {

        triangle1.createNewTriangle();
        triangle2.createNewTriangle();
    }

    @Override
    public void mousePressed(MouseEvent e) {
        draggable = false;
        if (triangle1.getPos().contains(e.getPoint())
                || triangle2.getPos().contains(e.getPoint())) {
            draggable = true;
            lastXPos = e.getX();
            lastYPos = e.getY();
        }
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        if (draggable) {
            isInside(triangle1, e);
            isInside(triangle2, e);
        }
    }

    private void isInside(Triangle t, MouseEvent e) {

        if (t.getPos().contains(e.getPoint()))
            updatePos(t, e);
    }

    //*****************************************************************
    //*** Next I try to do the right thing by only repainting the   ***   
    //*** portion of the panel that I use.                          ***
    //*** Well, almost. To make it as simple as possible for now    ***
    //*** I use a boundingbox rectangle and repaint within those    ***
    //*** bounds. The problem seem to be that the rest of the panel ***
    //*** does not want to repaint anything outside the bounding    ***
    //*** box, until I release the mousebutton(after click+dragging)***
    //*** When the mousebutton is released, a new triangle is created**
    //*** in the same spot. Se mousereleased method. Otherwise      ***
    //*** I would only be able to drag the triangle once            ***
    //*****************************************************************
    private void updatePos(Triangle t, MouseEvent event) {

        boundingBox = t.getPos().getBounds();

        // stored as final variables to avoid repeat invocations to methods.
        // is this a problem? Anybody care to explain?
        final int CURR_X = boundingBox.x;
        final int CURR_Y = boundingBox.y;
        final int CURR_W = boundingBox.width;
        final int CURR_H = boundingBox.height;
        final int OFFSET = 1;

        if ((CURR_X != event.getX()) || (CURR_Y != event.getY())) {

            // paint over the bounding-box of the old triangle
            repaint(CURR_X, CURR_Y, CURR_W + OFFSET, CURR_H + OFFSET);

            // update x-coordinates
            int xPos = event.getX();
            int[] xPoints = t.getPos().xpoints; // get old x coordinates
            for (int i = 0; i < xPoints.length; i++) {
                xPoints[i] = xPoints[i] - (lastXPos - xPos); // create new x
                                                             // coordinates
            }
            lastXPos = xPos;

            // update y-coordinates
            int yPos = event.getY();
            int[] yPoints = t.getPos().ypoints; // get old y coordinates
            for (int i = 0; i < yPoints.length; i++) {
                yPoints[i] = yPoints[i] - (lastYPos - yPos); // create new y
                                                             // coordinates
            }
            lastYPos = yPos;

            // paint inside bounding box of the new triangle
            repaint(boundingBox.x, boundingBox.y, boundingBox.width + OFFSET,
                    boundingBox.height + OFFSET);

            // repaint the whole panel (not recommended).
            // repaint(); //-> makes dragging the triangle sluggish.
        }
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.red);
        triangle1.draw(g);
        triangle2.draw(g);
    }

    // not used
    @Override
    public void mouseMoved(MouseEvent e) {
    }

    @Override
    public void mouseClicked(MouseEvent e) {
    }

    @Override
    public void mouseEntered(MouseEvent e) {
    }

    @Override
    public void mouseExited(MouseEvent e) {
    }

    /**
     * 
     * Inner Triangle Class.
     * A polygon object is used for convenience to
     * create the Triangle. Otherwise I would
     * have to deal with Points all through the program. Which means
     * 3 coordinate pairs = 6 coordinates, which
     * means more code.
     * 
     */
    private class Triangle {

        private Polygon polygon;

        private Triangle(Point p1, Point p2, Point p3) {

            polygon = new Polygon();
            polygon.addPoint(p1.x, p1.y);
            polygon.addPoint(p2.x, p2.y);
            polygon.addPoint(p3.x, p3.y);
        }

        public Polygon getPos() {
            return polygon;
        }

        public void createNewTriangle() {
            polygon = new Polygon(polygon.xpoints, polygon.ypoints,
                    polygon.npoints);
        }

        public void draw(Graphics g) {
            g.fillPolygon(polygon);
        }

    } // end inner class Triangle
} // end outer class TrianglePanel

为了您的方便，我提供了包含主方法的类(可从此处运行):

import java.awt.Dimension;
import javax.swing.JFrame;

public class TriangleFrame extends JFrame {

public TriangleFrame() {
    this.setTitle("Draggable triangles. Click one and drag it with the   mouse.");
    TrianglePanel panel = new TrianglePanel();
    panel.setPreferredSize(new Dimension(500, 500));
    this.add(panel);
    pack();
    setVisible(true);
}
public static void main(String[] args) {
    new TriangleFrame();

}

}

Answer 1

多边形缓存边界框。如果直接修改坐标，必须调用Polygon.invalidate() :

// paint inside bounding box of the new triangle
t.getPos().invalidate();
boundingBox = t.getPos().getBounds();
repaint(boundingBox);

但是，使用 Polygon.translate(int deltaX, int deltaY) 会更容易，它会为您完成所有工作。 (修改坐标并确保下次调用时边界框正确)。我还使用了repaint(Rectangle)。