java - 重新绘制 Swing 组件会产生糟糕的结果

Question

我“画”了一个组件来制作一种旋钮，因为我没有找到一种拥有“圆形 JSlider”的方法。我使用抗锯齿来获得良好的结果。当我用鼠标按下组件时，我修改光标位置并要求组件重新绘制。然后，问题出现了:重新绘制的结果很糟糕!

如果我要求仅在释放鼠标时重新绘制，结果似乎保持正确。但是，如果我在设置旋钮时不“连续”重新绘制组件，那么设置旋钮值会更复杂。

导致问题的“repaint”方法位于类末尾的 run 方法中。

有人已经遇到这个问题了吗？可以用什么样的方案来解决呢？这是我正在使用的代码:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.PointerInfo;
import java.awt.RadialGradientPaint;
import java.awt.RenderingHints;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;

import javax.swing.JFrame;
import javax.swing.JPanel;


public class Knob extends JPanel implements MouseListener {
int length, originX, originY, centerX, centerY, width, height, diameter, squareLength;
int minorTick, majorTick, xTick, yTick, xCursor, yCursor;
int xMouse, yMouse, xMouseOrigin, yMouseOrigin;
float yDeltaMouse;
double angleOrigin, angleRange, angle;
double angleCursorOrigin;
double angleCursorInitial;
Color backgroundColor, knobColor;
boolean mousePressed;
Thread t;

Knob () {
    System.out.println("Knob");
    angleCursorOrigin=0.5;
    angleCursorInitial=0.5;
    knobColor =new Color(0,255,0,255);      
    minorTick=9;
    majorTick=3;

    this.addMouseListener(this);
}

public void paintComponent (Graphics g) {
    width=this.getWidth()/10*10;
    height=this.getHeight()/10*10;

    Graphics2D g2D = (Graphics2D)g;
    System.setProperty("awt.useSystemAAFontSettings", "on");
    System.setProperty("swing.aatext", "true");
    g2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

    if (width>height) {
        length=height;
    } else {
        length=width;
    }
    centerX=width/2;
    centerY=height/2;

    g.setColor(Color.BLACK);
    squareLength = (int )(length*0.9);
    originX=(width-squareLength)/2;
    originY=(height-squareLength)/2;

    /*
    //-45 = (-(Math.PI)/4)
    angleOrigin= -45;
    // 270 = (3*(Math.PI)/2)
    angleRange=270;
    //g.drawRect(originX, originY, squareLength, squareLength);
    //g.fillArc(originX, originY, squareLength, squareLength, (int)angleOrigin, (int)angleRange);
    for (int i=0; i<minorTick ; i++) {
        angle=((i*angleRange/(minorTick-1))+angleOrigin)-7;
        //System.out.println(angle*360/(2*Math.PI));
        xTick= (int) (centerX+Math.cos(angle)*squareLength/2);
        yTick= (int) (centerY-Math.sin(angle)*squareLength/2);
        //g.drawLine(centerX, centerY, xTick, yTick);
        //g.fillArc(originX, originY, squareLength, squareLength, (int)angle, (int)14);
    }
    */

    angleOrigin=-(Math.PI)/4;
    angleRange=3*(Math.PI)/2;       
    g2D.setStroke(new BasicStroke(length/50+1));        
    for (int i=0; i<minorTick ; i++) {
        angle=i*angleRange/(minorTick-1)+angleOrigin;
        //System.out.println(angle*360/(2*Math.PI));
        xTick= (int) (centerX+Math.cos(angle)*squareLength/2);
        yTick= (int) (centerY-Math.sin(angle)*squareLength/2);
        //g.drawLine(centerX, centerY, xTick, yTick);
        g2D.draw (new Line2D.Float(centerX, centerY, xTick, yTick));
    }

    backgroundColor = this.getBackground();
    g.setColor(backgroundColor);
    diameter=(int)(length*0.8);
    originX=(width-diameter)/2;
    originY=(height-diameter)/2;
    g.fillOval(originX, originY, diameter, diameter);


    /*
    RadialGradientPaint gp;
    Point2D center= new Point2D.Float(width/2, height/2);
    diameter=(int)(length*0.75);
    originX=(width-diameter)/2;
    originY=(height-diameter)/2;
    float radius=diameter/2;        
    float[] dist = {0.7f, 1f};
    Color[] colors = {Color.BLUE, Color.GRAY};
    gp=new RadialGradientPaint(center, radius, dist, colors);
    g2D.setPaint(gp);       
    g2D.fillOval(originX,originY,diameter,diameter);
    */
    diameter=(int)(length*0.75);
    originX=(width-diameter)/2;
    originY=(height-diameter)/2;
    g.setColor(Color.GRAY);
    g.fillOval(originX,originY,diameter,diameter);

    diameter=(int)(length*0.6);
    originX=(width-diameter)/2;
    originY=(height-diameter)/2;
    g.setColor(knobColor);
    g.fillOval(originX,originY,diameter,diameter);

    g2D.setStroke(new BasicStroke(length/50+3));
    angle=(2*Math.PI)*(0.75-angleCursorOrigin*0.75)+angleOrigin;
    xCursor= (int) (centerX+Math.cos(angle)*length*0.35);
    yCursor= (int) (centerY-Math.sin(angle)*length*0.35);
    g.setColor(Color.GRAY);
    g2D.draw (new Line2D.Float(centerX, centerY, xCursor, yCursor));

}

@Override
public void mouseClicked(MouseEvent arg0) {
    // TODO Auto-generated method stub
    //System.out.println("Bouton : "+arg0.getButton());

}

@Override
public void mouseEntered(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mouseExited(MouseEvent arg0) {
    // TODO Auto-generated method stub

}

@Override
public void mousePressed(MouseEvent arg0) {
    // TODO Auto-generated method stub
    //System.out.println("Bouton : "+arg0.getButton());
    PointerInfo pointer = MouseInfo.getPointerInfo();
    Point mouseLocation = pointer.getLocation();
    xMouseOrigin = (int) mouseLocation.getX();
    yMouseOrigin = (int) mouseLocation.getY();
    if (arg0.getButton()==MouseEvent.BUTTON1) {
        mousePressed=true;
        t= new Thread(new TrackPosition());
        t.start();
    } else if (arg0.getButton()==MouseEvent.BUTTON3) {
        angleCursorOrigin=angleCursorInitial;
        repaint();
    }       
}

@Override
public void mouseReleased(MouseEvent arg0) {
    // TODO Auto-generated method stub
    mousePressed=false;
    //System.out.println("Mouse released");

    repaint();

}

class TrackPosition implements Runnable {

    @Override
    public void run() {
        // TODO Auto-generated method stub
        while (mousePressed==true) {
            PointerInfo pointer = MouseInfo.getPointerInfo();
            Point mouseLocation = pointer.getLocation();
            yMouse = (int) mouseLocation.getY();
            yDeltaMouse=(float)(yMouse-yMouseOrigin)/100;
            angleCursorOrigin=angleCursorOrigin+yDeltaMouse;
            yMouseOrigin=yMouse;
            if (angleCursorOrigin >=1) {
                angleCursorOrigin=1;
            } else if (angleCursorOrigin <= 0) {
                angleCursorOrigin=0;
            }
            //This repaint is a problem if I "uncomment" it
            //repaint();
        }

    }

}

/**
 * @param args
 */
public static void main(String[] args) {
    // TODO Auto-generated method stub
    JFrame frame = new JFrame();
    frame.setSize(300,90);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setContentPane(new Knob());
    frame.setVisible(true);

}

}

Answer 1

首先，在 paintComponent 方法中执行自定义绘制之前，您不会调用 super.paintComponent。

参见Painting in AWT and Swing和 Performing Custom Painting了解更多详情

然后转向这样一个事实:您的“鼠标跟踪线程”太过分了，实际上并不是必需的。相反，您应该使用 MouseMotionListener，请参阅 How to Write a Mouse Listener了解更多详情。

这将使您无需在本地和屏幕上下文之间进行转换。