asp.net中用C#自动生成透明的GIF图片

Posted on 2006-03-06 16:50 氧气中毒阅读(1880) 评论(0) 收藏举报

问题：

查遍网上资料，却没有关于在Asp.net中自动生成透明的GIF图片的代码。
值得大家探讨。
哪位高人能否解决这个问题？

解答：

作者:使名扬

方案1：最easy的方法利用css的滤镜

1.在aspx上拉一个HTML的img 然后run at server。同时为了体现透明，把背景色改成不同颜色自己看看效果。

如果整个GIF也要半透明可用 style="FILTER:alpha(opacity=50)"

</form>

</body>

2.codebehind的代码

using System;

using System.Collections;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Web;

using System.Web.SessionState;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.HtmlControls;

namespace dztz

{

///

/// test 的摘要说明。

///

public class test : System.Web.UI.Page

{

protected System.Web.UI.HtmlControls.HtmlImage IMG1;

private void Page_Load(object sender, System.EventArgs e)

{

MyTempImage myTempImage=new MyTempImage();

IMG1.Src=myTempImage.CreateImage();

}

Web 窗体设计器生成的代码

}

public class MyTempImage : Page

{

public string CreateImage()

{

string str=DateTime.Now.ToString();

Bitmap image=new Bitmap(200,30);

Graphics g=Graphics.FromImage(image);

string thefullname=Server.MapPath("/")+"\\nowtime.gif";

g.Clear(Color.Transparent); //这里用不用透明色无所谓的，透明色实际上会是黑色

g.DrawString(str,new Font("Courier New", 10),new

SolidBrush(Color.FromArgb(128, 0, 0, 255)),20,5); //这里采用半透明字体

image.Save(thefullname,System.Drawing.Imaging.ImageFormat.Gif);

return "/nowtime.gif";

}

方案2：生成一个真的透明背景的GIF图片（但是要调API，不推荐。）

Imports System.Runtime.InteropServices

Imports System

Imports System.IO

Imports System.Drawing

Imports System.Drawing.Imaging

Imports System.Drawing.Drawing2D

Public Class transparentGif : Inherits System.Web.UI.Page

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim pic As New System.Drawing.Bitmap(200, 200, PixelFormat.Format24bppRgb)

'''draw image

Dim blackpen As New Pen(Color.Black, 3)

Dim redpen As New Pen(Color.Red, 4)

Dim silverpen As New Pen(ColorTranslator.FromHtml("#CCCCCC"), 10)

Dim fBrush As SolidBrush = New SolidBrush(ColorTranslator.FromHtml("#0000FF"))

Dim g As Graphics = Graphics.FromImage(pic)

g.Clear(Color.White) ' blank the image

g.DrawLine(silverpen, 7, 80, 110, 80)

g.SmoothingMode = SmoothingMode.AntiAlias ' antialias objects

g.DrawString("TEST", New Font("verdana", 24, FontStyle.Bold), fBrush, New PointF(10, 50))

g.DrawEllipse(blackpen, 5, 5, 110, 110)

g.DrawEllipse(redpen, 1, 1, 118, 118)

'''save new image

pic = recolorGif(pic)

' set the content type

Response.ContentType = "image/gif"

' send the image to the viewer

pic.Save(Response.OutputStream, ImageFormat.Gif)

' tidy up

pic.Dispose()

End Sub

Private Function GetColorPalette() As ColorPalette

' Make a new Bitmap object to get its Palette.

Dim bitmap As Bitmap = New Bitmap(1, 1, PixelFormat.Format8bppIndexed)

Dim palette As ColorPalette = bitmap.Palette ' Grab the palette

bitmap.Dispose()

Return palette ' Send the palette back

End Function

Private Function recolorGif(ByVal image As Image) As Bitmap

Dim nColors As Integer = 16

' Make a new 8-BPP indexed bitmap that is the same size as the source image.

Dim Width As Integer = image.Width

Dim Height As Integer = image.Height

Dim bitmap As Bitmap = New Bitmap(Width, Height, PixelFormat.Format8bppIndexed)

' Create a color palette big enough to hold the colors you want.

Dim pal As ColorPalette = GetColorPalette()

' Initialize a new color table with entries

Dim i As Integer

' set palette the lazy way!

' replace with a proper color algorithm

For i = 0 To nColors - 1

pal.Entries(i) = Color.FromArgb(255, 100, 100, 100)

pal.Entries(0) = Color.FromArgb(255, 0, 0, 0)

pal.Entries(1) = Color.FromArgb(255, 255, 0, 0)

pal.Entries(2) = Color.FromArgb(255, 0, 255, 0)

pal.Entries(3) = Color.FromArgb(255, 0, 0, 255)

pal.Entries(4) = Color.FromArgb(255, 204, 204, 204)

pal.Entries(nColors - 1) = Color.FromArgb(0, 255, 255, 255)

'web safe palette use values =

'00 51 102 153 204 255

' Set the palette into the new Bitmap object.

bitmap.Palette = pal

Dim BmpCopy As Bitmap = New Bitmap(Width, Height, PixelFormat.Format32bppArgb)

Dim g As Graphics

g = Graphics.FromImage(BmpCopy)

g.PageUnit = GraphicsUnit.Pixel

' Transfer the Image to the Bitmap.

g.DrawImage(image, 0, 0, Width, Height)

' Force g to release its resources, namely BmpCopy.

g.Dispose()

' Lock a rectangular portion of the bitmap for writing.

Dim bitmapData As BitmapData

Dim rect As Rectangle = New Rectangle(0, 0, Width, Height)

bitmapData = bitmap.LockBits(rect, ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed)

' Copy the pixels from the source image

Dim pixels As IntPtr = bitmapData.Scan0

Dim bits As Byte() ' the buffer

Dim pBits As Int32

If (bitmapData.Stride > 0) Then

pBits = pixels.ToInt32()

Else

pBits = pixels.ToInt32() + bitmapData.Stride * (Height - 1)

End If

Dim stride As Integer = Math.Abs(bitmapData.Stride)

ReDim bits(Height * stride) ' Allocate the working buffer.

Dim row As Integer

Dim col As Integer

For row = 0 To Height - 1

For col = 0 To Width - 1

Dim pixel As Color

Dim i8BppPixel As Integer = row * stride + col

pixel = BmpCopy.GetPixel(col, row)

Dim colorIndex As Double

If pixel.R = 0 And pixel.G = 0 And pixel.B = 0 Then

colorIndex = 0

ElseIf pixel.R > 100 And pixel.G = 0 And pixel.B = 0 Then

colorIndex = 1

ElseIf pixel.G > 100 And pixel.R = 0 And pixel.B = 0 Then

colorIndex = 2

ElseIf pixel.B > 100 And pixel.R = 0 And pixel.G = 0 Then

colorIndex = 3

ElseIf pixel.B = 204 And pixel.R = 204 And pixel.G = 204 Then

colorIndex = 4

Else

colorIndex = (nColors - 1)

End If

bits(i8BppPixel) = CByte(colorIndex)

Next col

Next row

' Put the image bits definition into the bitmap.

Dim win32 As win32api = New win32api()

win32.CopyArrayTo(pBits, bits, Height * stride)

bitmap.UnlockBits(bitmapData)

Return bitmap

BmpCopy.Dispose()

bitmap.Dispose()

End Function

End Class

Public Class win32api

<DllImport("KERNEL32.DLL", EntryPoint:="RtlMoveMemory", _

SetLastError:=True, CharSet:=CharSet.Auto, _

ExactSpelling:=True, _

CallingConvention:=CallingConvention.StdCall)> _

Public Shared Sub CopyArrayTo(<[In](), MarshalAs(UnmanagedType.I4)> ByVal hpvDest As Int32, <[In](), Out()> ByVal hpvSource() As Byte, ByVal cbCopy As Integer)

' Leave function empty

End Sub

End Class

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asp.net中用C#自动生成透明的GIF图片