如何使用System.Drawing绘制透明图像? [英] How do you Draw Transparent Image using System.Drawing?

问题描述

我正在尝试从.aspx页返回透明的GIF，以在网页中显示.我试图使图像具有透明度，但我一直在使Black成为图像应该透明的位置.

I'm trying to return a transparent GIF from an .aspx page for display within a web page. I am trying to get the image to have transparency, but I just keep getting Black being where the image should be Transparent.

有人知道我在做什么吗?

Does anyone know what I'm doing wrong?

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
  Handles Me.Load
    '' Change the response headers to output a GIF image.
    Response.Clear()
    Response.ContentType = "image/gif"

    Dim width = 110
    Dim height = width

    '' Create a new 32-bit bitmap image
    Dim b = New Bitmap(width, height)

    '' Create Grahpics object for drawing
    Dim g = Graphics.FromImage(b)

    Dim rect = New Rectangle(0, 0, width - 1, height - 1)

    '' Fill in with Transparent
    Dim tbrush = New System.Drawing.SolidBrush(Color.Transparent)
    g.FillRectangle(tbrush, rect)

    '' Draw Circle Border
    Dim bPen = Pens.Red
    g.DrawPie(bPen, rect, 0, 365)

    '' Fill in Circle
    Dim cbrush = New SolidBrush(Color.LightBlue)
    g.FillPie(cbrush, rect, 0, 365)


    '' Clean up
    g.Flush()
    g.Dispose()

    '' Make Transparent
    b.MakeTransparent()

    b.Save(Response.OutputStream, Imaging.ImageFormat.Gif)
    Response.Flush()
    Response.End()
End Sub

推荐答案

不幸的是，没有一种简单的方法可以使用Bitmap对象创建透明的Gif. (请参见此知识库文章)

Unfortunately, there is no easy way to create a transparent Gif using a Bitmap object. (See this KB article)

您也可以在所使用的代码中使用支持透明度的PNG格式.

You can alternatively use the PNG format that supports transparency with the code you are using.

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