绘图程序的undo方法(Java)

Question

我正在尝试为一个基本的绘图程序创建一个撤销方法。目前，您可以更改画笔的大小和颜色，以及擦除。我试图通过将前一个屏幕保存为图像(最后一个)来撤消，当调用undo时，绘制该图像。我尝试了一些方法，但都不起作用。只需绘制图像"last“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模式的一些变体来处理历史记录。

Swing有一个简单的历史管理器，名为UndoManager。它通常用于文本编辑器，但它也可以很好地用于自定义命令。

如果您不想使用Swing，或者UndoManager不适合您的需求，那么可以尝试使用替代的独立解决方案，或者实现您自己的解决方案。用于大型跨平台应用程序的I also implemented my own。

所以，你应该把你所有的编辑方法包装到命令类中，这些命令类实现了一个公共接口(例如Command或UndoableEdit)，并且有"do“和"undo”的方法。

与文本文档相比，为图形实现命令更困难，因为在文本文档中，您只需要存储有关编辑的最少信息。将更改区域的矩形从原始图像存储在"do“上，并在"undo”上恢复。

Answer 2

你可以在每次按下鼠标时添加到撤销列表中，即使按下鼠标不会改变图像。

因此，当您单击undo选项时，您首先保存映像，然后恢复相同的映像。

您应该仅在用户实际修改图像之前保存到撤消列表。