Robot 实现屏幕抓图2

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主窗口的背景像素不是捕获的图像的一部分；就不可能把它们包含在修剪的图片内。因此，无论何时把背景像素包含在修剪区域内，操作都会失败，并且会给出一个“Out of bounds”错误信息。



    修剪操作由ImageArea的public Boolean crop()方法处理。如果完成了修剪或者没有选择子图像（当没有选中内容时调用这个方法是非常方便的）该方法（如下所示）返回true。如果在选择区域中包含了背景像素则返回false。

public boolean crop ()

{

   // There is nothing to crop if the selection rectangle is o­nly a single

   // point.



   if (srcx == destx && srcy == desty)

       return true;



   // Assume success.



   boolean succeeded = true;



   // Compute upper-left and lower-right coordinates for selection rectangle

   // corners.



   int x1 = (srcx < destx) ? srcx : destx;

   int y1 = (srcy < desty) ? srcy : desty;



   int x2 = (srcx > destx) ? srcx : destx;

   int y2 = (srcy > desty) ? srcy : desty;



   // Compute width and height of selection rectangle.



   int width = (x2-x1)+1;

   int height = (y2-y1)+1;



   // Create a buffer to hold cropped image.



   BufferedImage biCrop = new BufferedImage (width, height,  
 

                                             BufferedImage.TYPE_INT_RGB);

   Graphics2D g2d = biCrop.createGraphics ();



   // Perform the crop operation.



   try

   {

       BufferedImage bi = (BufferedImage) image;

       BufferedImage bi2 = bi.getSubimage (x1, y1, width, height);

       g2d.drawImage (bi2, null, 0, 0);

   }

   catch (RasterFormatException e)

   {

      succeeded = false;

   }



   g2d.dispose ();



   if (succeeded)

       setImage (biCrop); // Implicitly remove selection rectangle.
 
   else

   {

       // Prepare to remove selection rectangle.



       srcx = destx;

       srcy = desty;



       // Explicitly remove selection rectangle.



       repaint ();

   }



   return succeeded;

}
 

    crop()方法调用BufferedImage的public BufferedImage
getSubimage(int x, int y, int w, int
h)方法摘取选择区域内的子图像。如果该方法的参数没有指定BufferedImage内的图像，它就会抛出一个
java.awt.image.RasterFormatException，因此就会返回false。



图像保存


    Capture允许你把捕获的图像保存为一个jpeg文件。你通过一个保存文件选择器指定文件名，选择器由Capture类的构造函数创建：

// Construct a save file-chooser. Initialize the starting directory to

// the current directory, do not allow the user to select the "all files"

// filter, and restrict the files that can be selected to those ending

// with .jpg or .jpeg extensions.



final JFileChooser fcSave = new JFileChooser ();

fcSave.setCurrentDirectory (new File (System.getProperty ("user.dir")));

fcSave.setAcceptAllFileFilterUsed (false);

fcSave.setFileFilter (new ImageFileFilter ());
 

    为了限制文件选择器的选择是文件夹或者是以.jpg或.jpeg为后缀的文件，就使用了ImageFileFilter类的一个实例作为保存时文件选择器的文件过滤器。该方法对于任何非文件夹和后缀名非.jpg/.jpeg的文件都返回false：

public boolean accept (File f)

{

   // Allow the user to select directories so that the user can navigate the

   // file system.



   if (f.isDirectory ())

       return true;



   // Allow the user to select files ending with a .jpg or a .jpeg

   // extension.



   String s = f.getName ();

   int i = s.lastIndexOf ('.');



   if (i > 0 && i < s.length ()-1)

   {

       String ext = s.substring (i+1).toLowerCase ();



       if (ext.equals ("jpg") || ext.equals ("jpeg"))

           return true;

   }



   // Nothing else can be selected.



   return false;

}
 

    当你选择了Save As…菜单项时，它的监听器就会显示一个保存文件选择器。假定你没有退出选择器，监听器就会确保你选择的文件名是以.jpg或.jpeg为后缀名。继续，监听器会确定文件是否存在，这样你就不会无意中覆盖一个存在的文件。

// Present the "save" file-chooser without any file selected.

// If the user cancels this file-chooser, exit this method.



fcSave.setSelectedFile (null);

if (fcSave.showSaveDialog (Capture.this) !=

    JFileChooser.APPROVE_OPTION)

    return;



// Obtain the selected file. Validate its extension, which 

// must be .jpg or .jpeg. If extension not present, append

// .jpg extension.



File file = fcSave.getSelectedFile ();

String path = file.getAbsolutePath ().toLowerCase ();

if (!path.endsWith (".jpg") && !path.endsWith (".jpeg"))

    file = new File (path += ".jpg");



// If the file exists, inform the user, who might not want

// to accidentally overwrite an existing file. Exit method

// if the user specifies that it is not okay to overwrite

// the file.


if (file.exists ())

{

    int choice =  JOptionPane.

                  showConfirmDialog (null,

                                     "Overwrite file?",

                                     "Capture",

                                     JOptionPane.

                                     YES_NO_OPTION);
 

    if (choice == JOptionPane.NO_OPTION)

        return;

}