这是别人的程序的代码，帮我解释一下啊using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Windows.Forms;
using System.Reflection;
using AForge.Imaging.Filters;namespace IPLab
{
/// <summary>
/// FilterPreview window
/// </summary>
public class FilterPreview : System.Windows.Forms.Control
{
private Bitmap previewImage;
private Bitmap image;
private IFilter filter;
private Pen blackPen = new Pen( Color.Black, 1 );
private Cursor cursorHand;
private Cursor cursorHandMove; private int areaWidth, areaHeight;
private int imageX, imageY;
private bool tracking = false; private int startTrackingX, startTrackingY;
private int oldImageX, oldImageY; // Image property
[Browsable( false )]
public Bitmap Image
{
get { return image; }
set
{
image = value; if ( value != null )
{
// calculate size of preview area
areaWidth = Math.Min( ClientRectangle.Width - 2, image.Width );
areaHeight = Math.Min( ClientRectangle.Height - 2, image.Height ); // calculate image position
imageX = ( image.Width - areaWidth ) >> 1;
imageY = ( image.Height - areaHeight ) >> 1;
} RefreshFilter( );
}
}
// Filter property
[Browsable( false )]
public AForge.Imaging.Filters.IFilter Filter
{
set
{
filter = value;
RefreshFilter( );
}
} // Constructor
public FilterPreview( )
{
InitializeComponent( );
SetStyle( ControlStyles.AllPaintingInWmPaint | ControlStyles.ResizeRedraw |
ControlStyles.DoubleBuffer | ControlStyles.UserPaint, true );
// load cursors
Assembly assembly = this.GetType( ).Assembly;
cursorHand = new Cursor( assembly.GetManifestResourceStream( "IPLab.Resources.harrow.cur" ) );
cursorHandMove = new Cursor( assembly.GetManifestResourceStream( "IPLab.Resources.hmove.cur" ) );
} // Dispose
protected override void Dispose( bool disposing )
{
if ( disposing )
{
blackPen.Dispose( ); if ( previewImage != null )
{
previewImage.Dispose( );
cursorHand.Dispose( );
cursorHandMove.Dispose( );
}
}
base.Dispose( disposing );
} // Initialize control
private void InitializeComponent( )
{
this.MouseUp += new System.Windows.Forms.MouseEventHandler( this.FilterPreview_MouseUp );
this.MouseMove += new System.Windows.Forms.MouseEventHandler( this.FilterPreview_MouseMove );
this.MouseDown += new System.Windows.Forms.MouseEventHandler( this.FilterPreview_MouseDown );
} // Paint control
protected override void OnPaint( PaintEventArgs pe )
{
Graphics g = pe.Graphics;
Rectangle rc = ClientRectangle;
int width = rc.Width;
int height = rc.Height;
int x, y; // calculate size of preview area
if ( image != null )
{
width = areaWidth + 2;
height = areaHeight + 2;
}
// calculate position of preview area
x = ( rc.Width - width ) >> 1;
y = ( rc.Height - height ) >> 1; // draw rectangle
g.DrawRectangle( blackPen, x, y, width - 1, height - 1 ); x++;
y++; if ( image != null )
{
if ( previewImage == null )
{
// draw original image
g.DrawImage( image, new Rectangle( x, y, areaWidth, areaHeight ), imageX, imageY, areaWidth, areaHeight, GraphicsUnit.Pixel );
}
else
{
// draw preview image
g.DrawImage( previewImage, x, y, areaWidth, areaHeight );
}
} // Calling the base class OnPaint
base.OnPaint( pe );
} // Refresh preview
public void RefreshFilter( )
{
// release old image
if ( previewImage != null )
{
previewImage.Dispose( );
previewImage = null;
} if ( ( image != null ) && ( filter != null ) )
{
Bitmap tmp = image.Clone( new Rectangle( imageX, imageY, areaWidth, areaHeight ), image.PixelFormat ); try
{
previewImage = filter.Apply( tmp );
}
catch ( Exception )
{
} // release temp image
tmp.Dispose( );
} // repaint
Invalidate( );
} // On mouse move
private void FilterPreview_MouseMove( object sender, System.Windows.Forms.MouseEventArgs e )
{
if ( image != null )
{
if ( !tracking )
{
// calculate position of preview area
int x = ( ( ClientRectangle.Width - areaWidth - 2 ) >>1 ) + 1;
int y = ( ( ClientRectangle.Height - areaHeight - 2 ) >>1) + 1; // check mouse coordinates
if ( ( e.X >= x ) && ( e.Y >= y ) &&
( e.X < x + areaWidth ) && ( e.Y < y + areaHeight ) )
{
Cursor = cursorHand;
}
else
Cursor = Cursors.Default;
}
else
{
int dx = e.X - startTrackingX;
int dy = e.Y - startTrackingY; imageX = Math.Max( 0, Math.Min( image.Width - areaWidth, oldImageX - dx ) );
imageY = Math.Max( 0, Math.Min( image.Height - areaHeight, oldImageY - dy ) ); Invalidate( ); Cursor = cursorHandMove;
}
}
} // On mouse button down
private void FilterPreview_MouseDown( object sender, System.Windows.Forms.MouseEventArgs e )
{
if ( ( image != null ) && ( e.Button == MouseButtons.Left ) )
{
// start tracking
tracking = true;
Capture = true; startTrackingX = e.X;
startTrackingY = e.Y; oldImageX = imageX;
oldImageY = imageY; // release preview image
if ( previewImage != null )
{
previewImage.Dispose( );
previewImage = null;
}
// repaint
// Invalidate( ); // set cursor
Cursor = cursorHandMove;
}
} // On mouse button up
private void FilterPreview_MouseUp( object sender, System.Windows.Forms.MouseEventArgs e )
{
if ( tracking )
{
// stop tracking
tracking = false;
Capture = false; RefreshFilter( ); // set cursor
Cursor = cursorHand;
}
}
}
}
并设置标志
tracking = true; FilterPreview_MouseDown的时候判断标志
如果 tracking为true 计算要图片被移动到得新位置，并Invalidate( ); （重绘，会发消息调用OnPaint）
如果tracking为false救根据鼠标位置在矩形内 则变换鼠标形状
FilterPreview_MouseUp 设置标志位为false
OnPaint根据计算得到的位置绘制图片
然后将PictureBox放到Panel中，位置为(0,0)每次加载图片后，
设置PictureBox的大小与图片的大小相同，即
pictureBox.Size = pictureBox.Image.Size;
这样如果图片过大的话，会出现滚动条。楼主如果要更好一点的，就是当图片小于Panel的高度或宽度时居中的话
在加载图片后再计算一下PictureBox的位置就可以了。
g.DrawImage( image, new Rectangle( x, y, areaWidth, areaHeight ), imageX, imageY, areaWidth, areaHeight, GraphicsUnit.Pixel );
大概思路是这样的，PictureBox是固定的，然后定义一块画布，画布的大小跟PictureBox一样，但是画布每次描绘的图像不一样，即是根据原图和坐标重新绘画出来的，就是上一段代码。当你发生鼠标或者键盘事件时，更改绘画的坐标，这样就实现“拖动”效果了。