Graphics.GetHalftonePalette 方法

定义

命名空间:

System.Drawing

程序集:

System.Drawing.Common.dll

包:

System.Drawing.Common v8.0.0

Source:

Graphics.cs

获取当前 Windows 的半色调调色板的句柄。

public:
 static IntPtr GetHalftonePalette();

public static IntPtr GetHalftonePalette ();

static member GetHalftonePalette : unit -> nativeint

Public Shared Function GetHalftonePalette () As IntPtr

返回

IntPtr

nativeint

指定调色板的句柄的内部指针。

示例

下面的代码示例旨在与 Windows 窗体 一起使用，它需要 PaintEventArgse，这是事件处理程序的参数Paint。 此代码执行以下操作：

• 定义 Windows DLL 文件 gdi32.dll 的互操作性 DllImportAttribute 属性，其中包含必要的 GDI 函数。

• 将 SelectPalette DLL 中的 和 RealizePalette 函数定义为外部。

• 从现有图像文件 SampImag.jpg (创建图像，该文件必须与示例代码文件) 位于同一文件夹中，并将图像绘制到屏幕上。

• 创建内部指针类型变量，并分别将其值设置为图形对象的句柄和当前 Windows 半色调调色板。

• 选择并实现半色调调色板。

• 使用 hdc 参数创建新的图形对象。

• 再次绘制图像。

• 释放设备上下文的句柄。

结果是示例图像的两个呈现：一个具有 16 位调色板，一个具有 8 位调色板。

private:
   [System::Runtime::InteropServices::DllImportAttribute("gdi32.dll")]
   static IntPtr SelectPalette( IntPtr hdc, IntPtr htPalette, bool bForceBackground );

   [System::Runtime::InteropServices::DllImportAttribute("gdi32.dll")]
   static int RealizePalette( IntPtr hdc );

public:
   void GetHalftonePaletteVoid( PaintEventArgs^ e )
   {
      // Create and draw image.
      Image^ imageFile = Image::FromFile( "SampImag.jpg" );
      e->Graphics->DrawImage( imageFile, Point(0,0) );

      // Get handle to device context.
      IntPtr hdc = e->Graphics->GetHdc();

      // Get handle to halftone palette.
      IntPtr htPalette = Graphics::GetHalftonePalette();

      // Select and realize new palette.
      SelectPalette( hdc, htPalette, true );
      RealizePalette( hdc );

      // Create new graphics object.
      Graphics^ newGraphics = Graphics::FromHdc( hdc );

      // Draw image with new palette.
      newGraphics->DrawImage( imageFile, 300, 0 );

      // Release handle to device context.
      e->Graphics->ReleaseHdc( hdc );
   }

[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
private static extern IntPtr SelectPalette(
    IntPtr hdc,
    IntPtr htPalette,
    bool bForceBackground);
[System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")]
private static extern int RealizePalette(IntPtr hdc);

private void GetHalftonePaletteVoid(PaintEventArgs e)
{
    // Create and draw image.
    Image imageFile = Image.FromFile("SampImag.jpg");
    e.Graphics.DrawImage(imageFile, new Point(0, 0));

    // Get handle to device context.
    IntPtr hdc = e.Graphics.GetHdc();

    // Get handle to halftone palette.
    IntPtr htPalette = Graphics.GetHalftonePalette();

    // Select and realize new palette.
    SelectPalette(hdc, htPalette, true);
    RealizePalette(hdc);

    // Create new graphics object.
    Graphics newGraphics = Graphics.FromHdc(hdc);

    // Draw image with new palette.
    newGraphics.DrawImage(imageFile, 300, 0);

    // Release handle to device context.
    e.Graphics.ReleaseHdc(hdc);
}

<System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")> _
Private Shared Function SelectPalette(ByVal hdc As IntPtr, _
ByVal htPalette As IntPtr, ByVal bForceBackground As Boolean) As IntPtr
End Function

<System.Runtime.InteropServices.DllImportAttribute("gdi32.dll")> _
Private Shared Function RealizePalette(ByVal hdc As IntPtr) As Integer
End Function

<System.Security.Permissions.SecurityPermission( _
System.Security.Permissions.SecurityAction.LinkDemand, Flags:= _
System.Security.Permissions.SecurityPermissionFlag.UnmanagedCode)> _
Private Sub GetHalftonePaletteVoid(ByVal e As PaintEventArgs)

    ' Create and draw image.
    Dim imageFile As Image = Image.FromFile("SampImag.jpg")
    e.Graphics.DrawImage(imageFile, New Point(0, 0))

    ' Get handle to device context.
    Dim hdc As IntPtr = e.Graphics.GetHdc()

    ' Get handle to halftone palette.
    Dim htPalette As IntPtr = Graphics.GetHalftonePalette()

    ' Select and realize new palette.
    SelectPalette(hdc, htPalette, True)
    RealizePalette(hdc)

    ' Create new graphics object.
    Dim newGraphics As Graphics = Graphics.FromHdc(hdc)

    ' Draw image with new palette.
    newGraphics.DrawImage(imageFile, 300, 0)

    ' Release handle to device context.
    e.Graphics.ReleaseHdc(hdc)
End Sub

注解

该方法的目的是 GetHalftonePalette 在显示器使用每像素 8 位时，使 GDI+ 能够生成更高质量的半色调。 若要使用半色调调色板显示图像，请使用以下过程。