绘制程序的撤消方法(Java)

Question

我正在尝试为基本的绘画程序创建一个撤消方法。目前，您可以更改画笔的大小和颜色，并擦除。我正在尝试通过将上一个屏幕另存为图像（最后一个）来撤消，并在调用撤消时绘制该图像。我尝试了一些方法，但没有任何效果。只需将图像绘制"最后"即可创建与 clear 方法相同的效果。有什么想法吗？

import java.applet.*;
import java.util.*;
import java.awt.*;
import java.lang.Object.*;
public class Paint extends Applet
{
private int x;
private int y;
private int size = 10;
private int sides = 200;
private int color = 0;
private Rectangle red, orange, yellow, green, blue, purple, pink, black;
private Rectangle triangle, square, pentagon, hexagon, octagon, circle;
private Rectangle small, medium, large;
private Rectangle eraser, clear, undo;
private Rectangle menuBar;
private Image last;
private Graphics g2;
//defines rectangles
public void init()
{
  setSize(400,600);
  red = new Rectangle(0,0,25,25);
  orange = new Rectangle(0,25,25,25);
  yellow = new Rectangle(0,50,25,25);
  green = new Rectangle(0,75,25,25);
  blue = new Rectangle(0,100,25,25);
  purple = new Rectangle(0,125,25,25);
  pink = new Rectangle(0,150,25,25);
  black = new Rectangle(0,175,25,25);
  triangle = new Rectangle(0,200,25,25);
  square = new Rectangle(0,225,25,25);
  pentagon = new Rectangle(0,250,25,25);
  hexagon = new Rectangle(0,275,25,25);
  octagon = new Rectangle(0,300,25,25);
  circle = new Rectangle(0,325,25,25);
  small = new Rectangle(0,355,25,25);
  medium = new Rectangle(0,370,50,50);
  large = new Rectangle(0,420,100,100);
  eraser = new Rectangle(0,520,50,25);
  clear = new Rectangle(0,545,60,30);
  undo = new Rectangle(0,575,60,30);
  menuBar = new Rectangle(0,0,70,650);
}
//paints the blocks of color in the menu bar
public void paintColors(Graphics g)
{
  g.setColor(Color.red);
  g.fillRect(0,0,25,25);
  g.setColor(Color.orange);
  g.fillRect(0,25,25,25);
  g.setColor(Color.yellow);
  g.fillRect(0,50,25,25);
  g.setColor(Color.green);
  g.fillRect(0,75,25,25);
  g.setColor(Color.blue);
  g.fillRect(0,100,25,25);
  g.setColor(new Color(160,32,240));
  g.fillRect(0,125,25,25);
  g.setColor(Color.pink);
  g.fillRect(0,150,25,25);
  g.setColor(Color.black);
  g.fillRect(0,175,25,25);
}
//paints the shapes, eraser, clear, and undo in the menu bar
public void paintShapes(Graphics g)
{
  g.setColor(Color.black);
  Utility.fillTri(g,12,212,25);
  g.fillRect(2,227,20,20);
  Utility.fillPent(g,12,262,25);
  Utility.fillHex(g,12,287,25);
  Utility.fillOct(g,12,312,25);
  Utility.fillPoly(g,12,337,25,300);
  g.fillOval(2,355,10,10);
  g.fillOval(2,370,50,50);
  g.fillOval(2,420,100,100);
  g.setColor(Color.black);
  g.drawRect(1,521,52,26);
  g.setColor(Color.pink);
  g.fillRect(2,522,40,25);
  g.setColor(Color.black);
  g.setFont(new Font("Arial",Font.PLAIN,20));
  g.drawString("CLEAR",2,580);
  g.drawString("UNDO",2,610);
}
public void paint(Graphics g)
{ 
  g2 = getGraphics();
  g2.setColor(Color.white);
  g2.fillRect(0,0,60,getHeight());
  paintColors(g2);
  paintShapes(g2);
  draw(g2);
}
public void draw(Graphics g)
{
  getColor(g);
  Utility.fillPoly(g,x,y,size,sides); //fills a regular polygon with specified center, size, and number of sides
}
public boolean mouseDown(Event e, int xx, int yy)
{
    x = xx;
    y = yy;
  if(red.inside(xx,yy))
     color = 0;
  else if(orange.inside(xx,yy))
     color = 1;
  else if(yellow.inside(xx,yy))
     color = 2;
  else if(green.inside(xx,yy))
     color = 3;
  else if(blue.inside(xx,yy))
     color = 4;
  else if(purple.inside(xx,yy))
     color = 5;
  else if(pink.inside(xx,yy))
     color = 6;
  else if(black.inside(xx,yy))
     color = 7;
  if(triangle.inside(xx,yy))
     sides = 3;
  else if(square.inside(xx,yy))
     sides = 4;
  else if(pentagon.inside(xx,yy))  
     sides = 5;
  else if(hexagon.inside(xx,yy))
     sides = 6;
  else if(octagon.inside(xx,yy))
     sides = 7;
  else if(circle.inside(xx,yy))
     sides = 200;
  if(small.inside(xx,yy))
     size = 10;
  else if(medium.inside(xx,yy))
     size = 50;
  else if(large.inside(xx,yy))
     size = 100;
  if(eraser.inside(xx,yy))
     color = 8;
  if(clear.inside(xx,yy))  
     clear(g2);
  else if(undo.inside(xx,yy))
     undo(g2);
  if(!menuBar.inside(xx,yy))
     last = createImage(getWidth(),getHeight());
    return true;
}
public boolean mouseDrag(Event e, int xx, int yy)
{
    x = xx;
    y = yy;
  if(!menuBar.inside(xx,yy))
     repaint();
    return true;
}
public void update(Graphics g)
{
    paint(g);
}
public void clear(Graphics g)
{
  color = 8;
  getColor(g);
  g.fillRect(0,0,getWidth(),getHeight());
  color = 0;
  repaint();
}
public void undo(Graphics g)
{
{
public int getColor(Graphics g)
{
  switch(color){
  case 0: g.setColor(Color.red);
  break;
  case 1: g.setColor(Color.orange);
  break;
  case 2: g.setColor(Color.yellow);
  break;
  case 3: g.setColor(Color.green);
  break;
  case 4: g.setColor(Color.blue);
  break;
  case 5: g.setColor(new Color(160,32,240));
  break;
  case 6: g.setColor(Color.pink);
  break;
  case 7: g.setColor(Color.black);
  break;
  case 8: g.setColor(new Color(238,238,238));
  break;
  }
  return color;
}
}

Answer 1

我强烈建议使用Command模式的某种变体来处理历史记录。

Swing有一个简单的历史管理器，名为UndoManager。通常，它与文本编辑器一起使用，但它也可以与自定义命令一起使用。

如果您不想使用 Swing 或UndoManager不适合您的要求，请尝试使用替代的独立解决方案或实现您自己的解决方案。我还为一个大型跨平台应用程序实现了自己的应用程序。

因此，您应该将所有编辑方法包装到实现通用接口的命令类中（例如 Command或UndoableEdit）并具有"执行"和"撤消"的方法。

对于图形实现命令比对文本文档的命令更难，因为文本文档只需要存储有关编辑的最少信息。 将原始图像中更改区域的矩形存储在"do"上，并在"撤消"上恢复。

Answer 2

每次

鼠标按下时都会添加到撤消列表中，即使鼠标按下不会更改图像。

因此，当您单击撤消选项时，您首先保存图像，然后恢复相同的图像。

您应该仅在用户实际修改图像之前保存到撤消列表。