这里需要两个ASP.NET页面：Zoom.aspx和ZoomProcessor.aspx。ZoomProcessor.aspx用于实际的图片操 作。这个页面输出的不是HTML，而是图象。这个输出图象就作为Zoom.aspx的图象源，然后在Zoom.aspx页面通过按钮控件来缩放、漫游和显 示图象。通过下面的内容，将向你介绍功能及其细节。你可能还会注意到重画图象的用时会更长一些。这主要是因为图象是在服务器端被创建的。如果我们把图象放 到一个稍小一点的窗口里，而且这个窗口没有HTML在它的下面或右边，那么我们也许就会把注意力转移到其它地方了。
Zoom.aspx design:
<table>Zoom.aspx code-behind.
<tr>
<td vAlign="top">
<table>
<tr>
<td></td>
<td><asp:imagebutton id="btnUp" runat="server" ImageUrl="Up.jpg"
AlternateText="Up"></asp:imagebutton></td>
<TD></TD>
</tr>
<tr>
<td><asp:imagebutton id="btnLeft" runat="server" ImageUrl="left.jpg"
AlternateText="Left"></asp:imagebutton></td>
<td><asp:imagebutton id="btnReset" runat="server" imageurl="reset.jpg">
</asp:imagebutton></td>
<TD><asp:imagebutton id="btnRight" runat="server" ImageUrl="right.jpg"
AlternateText="Right"></asp:imagebutton></TD>
</tr>
<tr>
<td></td>
<td><asp:imagebutton id="btnDown" runat="server" ImageUrl="down.jpg"
AlternateText="Down"></asp:imagebutton></td>
<TD></TD>
</tr>
<tr>
<td><asp:imagebutton id="btnOut" runat="server" ImageUrl="out.jpg"
AlternateText="Out"></asp:imagebutton></td>
<td></td>
<td><asp:imagebutton id="btnZoom" runat="server" ImageUrl="in.jpg"
AlternateText="In"></asp:imagebutton></td>
</tr>
</table>
<input id="hx" type="hidden" runat="server" NAME="hx"><input id="hy"
type="hidden" runat="server" NAME="hy">
</td>
<td><asp:imagebutton id="btnMainImage" runat="server" ImageUrl="">
</asp:imagebutton></td>
</tr>
</table>
#Region " Properties "ZoomProcessor.aspx code-behind.
'X holds the x coordinate of the
'center of the image
Public Property X() As Integer
Get
Return CInt(viewstate("x"))
End Get
Set(ByVal Value As Integer)
viewstate("x") = Value
End Set
End Property
'Y holds the y coordinate of the
'center of the image
Public Property Y() As Integer
Get
Return CInt(viewstate("y"))
End Get
Set(ByVal Value As Integer)
viewstate("y") = Value
End Set
End Property
'Z holds the Zoom Level
Public Property Z() As Integer
Get
Return CInt(viewstate("Z"))
End Get
Set(ByVal Value As Integer)
If Value < 1 Then Value = 1
viewstate("Z") = Value
End Set
End Property
'ImageWidth holds the original image width
Public Property ImageWidth() As Integer
Get
Return CInt(viewstate("ImageWidth"))
End Get
Set(ByVal Value As Integer)
viewstate("ImageWidth") = Value
End Set
End Property
'ImageHeight hods the original image height
Public Property ImageHeight() As Integer
Get
Return CInt(viewstate("ImageHeight"))
End Get
Set(ByVal Value As Integer)
viewstate("ImageHeight") = Value
End Set
End Property
#End Region
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As _
System.EventArgs) Handles MyBase.Load
If Not IsPostBack() Then
'On the first page load, we need to know
'the origanal image's size and get the
'center x and y coordinates
Dim i As System.Drawing.Image = _
System.Drawing.Image.FromFile(Server.MapPath("." & _
"\" & "biglogo" & ".jpg"))
ImageWidth = i.Width
ImageHeight = i.Height
X = CInt(ImageWidth / 2)
Y = CInt(ImageHeight / 2)
Z = 1
i.Dispose()
getimage()
End If
End Sub
Private Sub btnMainImage_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnMainImage.Click
If Z = 1 Then
X = e.X
Y = e.Y
Z = 2
Else
X = CInt(hx.Value) - CInt((CInt(ImageWidth / 2) - e.X) / Z)
Y = CInt(hy.Value) - CInt((CInt(ImageHeight / 2) - e.Y) / Z)
End If
getimage()
End Sub
Private Sub btnReset_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnReset.Click
X = CInt(ImageWidth / 2)
Y = CInt(ImageHeight / 2)
Z = 1
getimage()
End Sub
Private Sub btnLeft_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnLeft.Click
X = X - 20
getimage()
End Sub
Private Sub btnRight_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnRight.Click
X = X + 20
getimage()
End Sub
Private Sub btnUp_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnUp.Click
Y = Y - 20
getimage()
End Sub
Private Sub btnDown_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnDown.Click
Y = Y + 20
getimage()
End Sub
Private Sub btnZoom_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnZoom.Click
If Z < 8 Then
Z = Z * 2
End If
getimage()
End Sub
Private Sub btnOut_Click(ByVal sender As System.Object, ByVal e As _
System.Web.UI.ImageClickEventArgs) Handles btnOut.Click
If Z > 1 Then
Z = CInt(Z / 2)
End If
getimage()
End Sub
Private Sub getimage()
Dim ImageName As String = "biglogo"
Dim srcx, srcy As Integer
'Convert X Value to Top Left of image
srcx = X - CInt(CInt(ImageWidth / 2) / Z)
If srcx < 0 Then srcx = 0
If srcx > ImageWidth Then srcx = ImageWidth
'Convert Y value to Top Left of Image
srcy = Y - CInt(CInt(ImageHeight / 2) / Z)
If srcy < 0 Then srcy = 0
If srcy > ImageHeight Then srcy = ImageHeight
'Set the source of the Image to be our Processing aspx page
btnMainImage.ImageUrl = "zoomProcessor.aspx?x=" & srcx & _
"&y=" & srcy & "&z=" & Z & "&img=" & ImageName
hx.Value = X.ToString
hy.Value = Y.ToString
'Enable/disable buttons
If srcx > 0 Then
btnLeft.Enabled = True
Else
btnLeft.Enabled = False
End If
If srcy > 0 Then
btnUp.Enabled = True
Else
btnUp.Enabled = False
End If
If Z = 1 Then
btnOut.Enabled = False
Else
btnOut.Enabled = True
End If
If Z = 8 Then
btnZoom.Enabled = False
Else
btnZoom.Enabled = True
End If
End Sub
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As _
System.EventArgs) Handles MyBase.Load
'Create a new Image object from our source image
Dim i As System.Drawing.Image = _
System.Drawing.Image.FromFile(Server.MapPath("./" _
& Request("img") & ".jpg"))
'Create a workable bitmap image
Dim b As New System.Drawing.Bitmap(CInt(i.Width), _
CInt(i.Height), System.Drawing.Imaging.PixelFormat.Format24bppRgb)
'Place the bitmap image in a Graphics object
Dim g As Graphics = Graphics.FromImage(b)
'Set the default image background color
g.Clear(Color.White)
'Crop the main image
'Get Coordinates and Zoom Values from querystring
Dim x As Integer = CInt(Request("X"))
Dim Y As Integer = CInt(Request("y"))
Dim Z As Integer = CInt(Request("z"))
'Create 2 rectangles. We can grab a rectangle portion
'of the original image and stretch it to fit the size
'of the larger rectangle.
Dim src As New Rectangle()
Dim dst As New Rectangle()
'Set Source rectangle properties
src.X = x
src.Y = Y
src.Width = CInt(i.Width / Z)
src.Height = CInt(i.Height / Z)
'Set Destination rectangle properties
dst.X = 0
dst.Y = 0
dst.Width = CInt(i.Width)
dst.Height = CInt(i.Height)
'Create the image from our rectangles
g.DrawImage(i, dst, src, GraphicsUnit.Pixel)
'Set the content type
Response.ContentType = "image/jpeg"
'Save the image as the Output of this page
b.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg)
'Clean Up
src = Nothing
dst = Nothing
g = Nothing
b = Nothing
i = Nothing
End Sub
