问题描述
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.List;
import java.util.ArrayList;
class DrawningBoard extends Canvas implements MouseMotionListener{
private List<Point> points = new ArrayList<>();
private List<List<Point>> curves = new ArrayList<>();
private boolean isRectangle = false;
private int xr,yr,widthr,heightr;
public void setIsRectangle(boolean trueOrFalse){
isRectangle = trueOrFalse;
}
public boolean getIsRectangle(){
return isRectangle;
}
public DrawningBoard(){
setBackground(Color.magenta);
addMouseMotionListener(this);
addMouseListener(new MouseAdapter(){
public void mouseReleased(MouseEvent e){
curves.add(points);
points = new ArrayList<>();
}
public void mousepressed(MouseEvent e){
points.add(new Point(e.getX(),e.getY()));
}
});
}
public void paint(Graphics g){
g.setColor(Color.CYAN);
if(isRectangle){
g.drawRect(xr,heightr);
}
for(List<Point> curve : curves){
for(int i = 0; i < curve.size() - 1; i++){
g.drawLine((int)curve.get(i).getX(),(int)curve.get(i).getY(),(int)curve.get(i + 1).getX(),(int)curve.get(i + 1).getY());
}
}
}
public void mouseDragged(MouseEvent e){
Graphics g = getGraphics();
g.setColor(Color.CYAN);
int xx = e.getX();
int yy = e.getY();
int x = (int)points.get(points.size() - 1).getX();
int y = (int)points.get(points.size() - 1).getY();
int dx = xx-x;
int dy = yy-y;
if(isRectangle){
if(dx >= 0 && dy >= 0){
xr = x;
yr = y;
widthr = dx;
heightr = dy;
} else if(dx < 0 && dy < 0){
xr = xx;
yr = yy;
widthr = -dx;
heightr = -dy;
} else if(dx >= 0 && dy < 0){
xr = x;
yr = yy;
widthr = dx;
heightr = -dy;
} else if(dx < 0 && dy >= 0){
xr = xx;
yr = y;
widthr = -dx;
heightr = dy;
}
repaint();
}
else {
g.drawLine(xx,yy,(int)points.get(points.size() - 1).getX(),(int)points.get(points.size() - 1).getY());
points.add(new Point(xx,yy));
}
}
public void mouseMoved(MouseEvent e) { }
}
class GUI extends JFrame implements ActionListener{
private JPanel[] panel;
private JButton[] button;
private DrawningBoard board;
public GUI(String title){
super(title);
setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
setSize(416,400);
board = new DrawningBoard();
board.setBounds(0,400,400);
panel = new JPanel[3];
panel[0] = new JPanel();
panel[1] = new JPanel();
panel[2] = new JPanel();
panel[0].setLayout(null);
panel[1].setLayout(null);
panel[2].setLayout(null);
panel[0].setBounds(0,20);
panel[1].setBounds(0,20,400);
panel[2].add(panel[0]);
panel[2].add(panel[1]);
panel[0].setBackground(Color.red);
button = new JButton[5];
button[0] = new JButton("Rectangle");
button[1] = new JButton("b1");
button[2] = new JButton("b2");
button[3] = new JButton("b3");
button[4] = new JButton("b4");
button[0].addActionListener(this);
button[3].addActionListener(this);
button[0].setBounds(0,100,20);
button[1].setBounds(100,20);
button[2].setBounds(200,20);
button[3].setBounds(300,20);
button[4].setBounds(0,20);
panel[0].add(button[0]);
panel[0].add(button[1]);
panel[0].add(button[2]);
panel[0].add(button[3]);
panel[0].add(button[4]);
panel[1].add(board);
add(panel[2]);
show();
}
public void actionPerformed(ActionEvent e){
String command = e.getActionCommand();
if(command.equals("Rectangle"))
board.setIsRectangle(!board.getIsRectangle());
}
}
public class Paint{
public static void main(String []str){
new GUI("Paint");
}
}
我想创建一个Paint应用程序。如果我在板上绘制了多条曲线,然后又想绘制一个
矩形(使用drawRect(x,y,width,height)
),这些曲线将被重新粉刷,并由于使用repaint()
方法而导致一些冲洗。如何避免潮红?
我尝试使用update()
方法,但是在拖动鼠标时会绘制许多矩形。
解决方法
Swing默认为双缓冲。
public void paint(Graphics g){
不要覆盖paint()。您这样做不正确,并且失去了双重缓冲的好处。
相反,自定义绘画应通过重写paintComponent(...)
方法来完成。阅读有关demo's github documentation的Swing教程中的部分,以获取更多信息和工作示例。
您还可以从Custom Painting中查看DrawOnComponent
的示例,以获取满足您需要的更完整的示例。