Bitmap.MakeTransparent 方法

定义

命名空间:

System.Drawing

程序集:

System.Drawing.Common.dll

使此 Bitmap的默认透明颜色透明。

重载

MakeTransparent()	使此 Bitmap的默认透明颜色透明。
MakeTransparent(Color)	使此 Bitmap的指定颜色透明。

MakeTransparent()

使此 Bitmap的默认透明颜色透明。

public:
 void MakeTransparent();

public void MakeTransparent ();

member this.MakeTransparent : unit -> unit

Public Sub MakeTransparent ()

例外

InvalidOperationException

Bitmap 的图像格式是图标格式。

Exception

操作失败。

示例

下面的代码示例设计用于 Windows 窗体，它需要 PaintEventArgse，这是 Paint 事件处理程序的参数。 该代码使系统默认透明色 myBitmap，然后将 Bitmap 绘制到屏幕。

private:
   void MakeTransparent_Example1( PaintEventArgs^ e )
   {
      // Create a Bitmap object from an image file.
      Bitmap^ myBitmap = gcnew Bitmap( "Grapes.gif" );

      // Draw myBitmap to the screen.
      e->Graphics->DrawImage( myBitmap, 0, 0, myBitmap->Width, myBitmap->Height );

      // Make the default transparent color transparent for myBitmap.
      myBitmap->MakeTransparent();

      // Draw the transparent bitmap to the screen.
      e->Graphics->DrawImage( myBitmap, myBitmap->Width, 0, myBitmap->Width, myBitmap->Height );
   }

private void MakeTransparent_Example1(PaintEventArgs e)
{

    // Create a Bitmap object from an image file.
    Bitmap myBitmap = new Bitmap("Grapes.gif");

    // Draw myBitmap to the screen.
    e.Graphics.DrawImage(myBitmap, 0, 0, myBitmap.Width,
        myBitmap.Height);

    // Make the default transparent color transparent for myBitmap.
    myBitmap.MakeTransparent();

    // Draw the transparent bitmap to the screen.
    e.Graphics.DrawImage(myBitmap, myBitmap.Width, 0,
        myBitmap.Width, myBitmap.Height);
}

Private Sub MakeTransparent_Example1(ByVal e As PaintEventArgs)

    ' Create a Bitmap object from an image file.
    Dim myBitmap As New Bitmap("Grapes.gif")

    ' Draw myBitmap to the screen.
    e.Graphics.DrawImage(myBitmap, 0, 0, myBitmap.Width, _
    myBitmap.Height)

    ' Make the default transparent color transparent for myBitmap.
    myBitmap.MakeTransparent()

    ' Draw the transparent bitmap to the screen.
    e.Graphics.DrawImage(myBitmap, myBitmap.Width, 0, myBitmap.Width, _
    myBitmap.Height)
End Sub

注解

系统调色板将一种颜色定义为默认透明或 alpha 颜色。 此方法使此 Bitmap的默认透明颜色透明。 如果未由系统指定透明颜色，则 LightGray 为透明颜色。

调用 MakeTransparent时，位图将转换为 Format32bppArgb 格式，因为此格式支持 alpha 通道。

MakeTransparent(Color)

使此 Bitmap的指定颜色透明。

public:
 void MakeTransparent(System::Drawing::Color transparentColor);

public void MakeTransparent (System.Drawing.Color transparentColor);

member this.MakeTransparent : System.Drawing.Color -> unit

Public Sub MakeTransparent (transparentColor As Color)

参数

transparentColor

Color

表示透明颜色的 Color 结构。

例外

InvalidOperationException

Bitmap 的图像格式是图标格式。

Exception

操作失败。

示例

下面的代码示例设计用于 Windows 窗体，它需要 PaintEventArgse，这是 Paint 事件处理程序的参数。 该代码执行以下操作：

• 获取 Bitmap中像素的颜色。

• 使位图的颜色透明。

• 将 Bitmap 绘制到屏幕。

private:
   void MakeTransparent_Example2( PaintEventArgs^ e )
   {
      // Create a Bitmap object from an image file.
      Bitmap^ myBitmap = gcnew Bitmap( "Grapes.gif" );

      // Draw myBitmap to the screen.
      e->Graphics->DrawImage( myBitmap, 0, 0, myBitmap->Width, myBitmap->Height );

      // Get the color of a background pixel.
      Color backColor = myBitmap->GetPixel( 1, 1 );

      // Make backColor transparent for myBitmap.
      myBitmap->MakeTransparent( backColor );

      // Draw the transparent bitmap to the screen.
      e->Graphics->DrawImage( myBitmap, myBitmap->Width, 0, myBitmap->Width, myBitmap->Height );
   }

private void MakeTransparent_Example2(PaintEventArgs e)
{

    // Create a Bitmap object from an image file.
    Bitmap myBitmap = new Bitmap("Grapes.gif");

    // Draw myBitmap to the screen.
    e.Graphics.DrawImage(
        myBitmap, 0, 0, myBitmap.Width, myBitmap.Height);

    // Get the color of a background pixel.
    Color backColor = myBitmap.GetPixel(1, 1);

    // Make backColor transparent for myBitmap.
    myBitmap.MakeTransparent(backColor);

    // Draw the transparent bitmap to the screen.
    e.Graphics.DrawImage(
        myBitmap, myBitmap.Width, 0, myBitmap.Width, myBitmap.Height);
}

Private Sub MakeTransparent_Example2(ByVal e As PaintEventArgs)

    ' Create a Bitmap object from an image file.
    Dim myBitmap As New Bitmap("Grapes.gif")

    ' Draw myBitmap to the screen.
    e.Graphics.DrawImage(myBitmap, 0, 0, myBitmap.Width, _
        myBitmap.Height)

    ' Get the color of a background pixel.
    Dim backColor As Color = myBitmap.GetPixel(1, 1)

    ' Make backColor transparent for myBitmap.
    myBitmap.MakeTransparent(backColor)

    ' Draw the transparent bitmap to the screen.
    e.Graphics.DrawImage(myBitmap, myBitmap.Width, 0, myBitmap.Width, _
        myBitmap.Height)
End Sub

注解

调用 MakeTransparent时，位图将转换为 Format32bppArgb 格式，因为此格式支持 alpha 通道。