问题
I know that this has been asked many times before, but every time I visit the question thread and excecute the posed solution, it still doesn't work for me.
So before I create any confusion, the problem I have is that the screen I draw is constantly flashing, this is because every time I draw the screen, I clear the screen with a completely white filled rectangle, the things I draw over the rectangle will flash.
Here is my code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.geom.*;
import javax.swing.Timer.*;
/**
*
* beschrijving
*
* @version 1.0 van 16-6-2016
* @author
*/
public class shadows3 extends JApplet implements ActionListener{
// Begin variabelen
int[] loc = new int[2];
int[][] wall = new int[10][8];
// Einde variabelen
public void init() {
Container cp = getContentPane();
cp.setLayout(null);
cp.setBounds(0, 0, 600, 600);
// Begin componenten
for (int a=0; a<10; a++) {
int tempx = (int) (Math.random()*20)*30;
int tempy = (int) (Math.random()*20)*30;
wall[a][0] = tempx;
wall[a][1] = tempy;
wall[a][2] = tempx+30;
wall[a][3] = tempy;
wall[a][4] = tempx+30;
wall[a][5] = tempy+30;
wall[a][6] = tempx;
wall[a][7] = tempy+30;
} // end of for
loc[0] = 300;
loc[1] = 300;
Timer step = new Timer(20, this);
step.start();
// Einde componenten
} // end of init
private int length(int x1, int y1, int x2, int y2) {
double distance = Math.sqrt(Math.pow(x1-x2,2)+Math.pow(y1-y2,2));
return (int) distance;
}
// Begin eventmethoden
public void paint (Graphics g){
g.setColor(Color.WHITE);
g.fillRect(0,0,600,600);
int[] xpoints = new int[8];
int[] ypoints = new int[8];
int[] list = new int[3];
for (int a=0; a<5; a++) {
for (int b=0; b<4; b++) {
if (length(wall[a][b*2],wall[a][b*2+1],loc[0],loc[1])==Math.max(Math.max(length(wall[a][0],wall[a][1],loc[0],loc[1]),
length(wall[a][2],wall[a][3],loc[0],loc[1])),
Math.max(length(wall[a][4],wall[a][5],loc[0],loc[1]),
length(wall[a][6],wall[a][7],loc[0],loc[1])))) {
int temp = b;
for (int c=0; c<3; c++) {
temp += 1;
if (temp == 4) {
temp = 0;
} // end of if
list[c] = temp;
} // end of for
} // end of if
} // end of for
xpoints[0] = wall[a][list[0]*2 ];
ypoints[0] = wall[a][list[0]*2+1];
xpoints[1] = wall[a][list[1]*2 ];
ypoints[1] = wall[a][list[1]*2+1];
xpoints[2] = wall[a][list[2]*2 ];
ypoints[2] = wall[a][list[2]*2+1];
xpoints[3] = wall[a][list[2]*2 ]+(wall[a][list[2]*2 ]-loc[0])*10000;
ypoints[3] = wall[a][list[2]*2+1]+(wall[a][list[2]*2+1]-loc[1])*10000;
xpoints[4] = wall[a][list[0]*2 ]+(wall[a][list[0]*2 ]-loc[0])*10000;
ypoints[4] = wall[a][list[0]*2+1]+(wall[a][list[0]*2+1]-loc[1])*10000;
g.setColor(Color.BLACK);
g.fillPolygon(xpoints, ypoints, 5);
//g.fillRect(wall[a][0],wall[a][1],30,30);
} // end of for
}
//@Override
public void actionPerformed(ActionEvent e){
loc[0] += 4;
loc[1] += 2;
repaint();
}
// Einde eventmethoden
} // end of class shadows3
If you're wondering what I'm trying to create, it's some kind of real-time shadows engine, it's fairly slow but it's just a fun project, the screen flashing is a real problem though for many of my projects.
Many thanks in advance!
回答1:
Because you should be migrating to a plugin-free environment, consider a hybrid deployed via java-web-start. The example below displays your content in a JPanel, which is double buffered by default. In particular,
Invoke super.paintComponent() to avoid rendering artifacts.
Override getPreferredSize() to establish the initial size.
Instantiate Random with a constant seed for easier debugging.
The
applettag in a comment allows easy testing, as shown here.
Test:
$ javac ShadowApplet.java ; appletviewer ShadowApplet.java
Code:
//<applet code="ShadowApplet.class" width=600 height=600></applet>
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import javax.swing.JApplet;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
/**
* @see https://stackoverflow.com/a/37958844/230513
*/
public class ShadowApplet extends JApplet {
private static final Random R = new Random(42);
@Override
public void init() {
EventQueue.invokeLater(() -> {
add(new ShadowPanel());
});
}
public static void main(String[] args) {
EventQueue.invokeLater(new ShadowApplet()::display);
}
private void display() {
JFrame f = new JFrame("Test");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new ShadowPanel());
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
}
private static class ShadowPanel extends JPanel implements ActionListener {
int[] loc = new int[2];
int[][] wall = new int[10][8];
public ShadowPanel() {
this.setLayout(null);
this.setBackground(Color.WHITE);
for (int a = 0; a < 10; a++) {
int tempx = R.nextInt(20) * 30;
int tempy = R.nextInt(20) * 30;
wall[a][0] = tempx;
wall[a][1] = tempy;
wall[a][2] = tempx + 30;
wall[a][3] = tempy;
wall[a][4] = tempx + 30;
wall[a][5] = tempy + 30;
wall[a][6] = tempx;
wall[a][7] = tempy + 30;
}
loc[0] = 300;
loc[1] = 300;
Timer step = new Timer(20, this);
step.start();
}
private int length(int x1, int y1, int x2, int y2) {
double distance = Math.sqrt(Math.pow(x1 - x2, 2) + Math.pow(y1 - y2, 2));
return (int) distance;
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
int[] xpoints = new int[8];
int[] ypoints = new int[8];
int[] list = new int[3];
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 4; b++) {
if (length(wall[a][b * 2], wall[a][b * 2 + 1], loc[0],
loc[1]) == Math.max(Math.max(length(wall[a][0], wall[a][1], loc[0], loc[1]),
length(wall[a][2], wall[a][3], loc[0], loc[1])),
Math.max(length(wall[a][4], wall[a][5], loc[0], loc[1]),
length(wall[a][6], wall[a][7], loc[0], loc[1])))) {
int temp = b;
for (int c = 0; c < 3; c++) {
temp += 1;
if (temp == 4) {
temp = 0;
}
list[c] = temp;
}
}
}
xpoints[0] = wall[a][list[0] * 2];
ypoints[0] = wall[a][list[0] * 2 + 1];
xpoints[1] = wall[a][list[1] * 2];
ypoints[1] = wall[a][list[1] * 2 + 1];
xpoints[2] = wall[a][list[2] * 2];
ypoints[2] = wall[a][list[2] * 2 + 1];
xpoints[3] = wall[a][list[2] * 2] + (wall[a][list[2] * 2] - loc[0]) * 10000;
ypoints[3] = wall[a][list[2] * 2 + 1] + (wall[a][list[2] * 2 + 1] - loc[1]) * 10000;
xpoints[4] = wall[a][list[0] * 2] + (wall[a][list[0] * 2] - loc[0]) * 10000;
ypoints[4] = wall[a][list[0] * 2 + 1] + (wall[a][list[0] * 2 + 1] - loc[1]) * 10000;
g.setColor(Color.BLACK);
g.fillPolygon(xpoints, ypoints, 5);
g.fillRect(wall[a][0], wall[a][1], 30, 30);
}
}
@Override
public void actionPerformed(ActionEvent e) {
loc[0] += 4;
loc[1] += 2;
repaint();
}
@Override
public Dimension getPreferredSize() {
return new Dimension(600, 600);
}
}
}
回答2:
You need to create a separate image to draw all things on:
im=createImage(getWidth(), getHeight());
in init.
Then in your paint:
Graphics g2=im.getGraphics();
g2.setColor(Color.WHITE);
g2.fillRect(0,0,600,600);
and continue with all the g commands replaced with g2:
g2.setColor(Color.BLACK);
g2.fillPolygon(xpoints, ypoints, 5);
then you draw the image on g:
g.drawImage(im, 0, 0, this);
and you have an update method:
public void update(Graphics g) { paint(g); }
来源：https://stackoverflow.com/questions/37954011/graphics-flashing-in-japplet