Graphics.GetHalftonePalette 方法

public:
 static IntPtr GetHalftonePalette();

public static IntPtr GetHalftonePalette();

static member GetHalftonePalette : unit -> nativeint

Public Shared Function GetHalftonePalette () As IntPtr

傳回

內部指標，指定調色盤的 handle。

範例

以下程式碼範例是為 Windows Forms 設計的，並需要 PaintEventArgse，這是 Paint 事件處理程序的參數。 此程式碼會執行下列動作：

• 定義Windows DLL檔案 gdi32.dll的互通性DllImportAttribute屬性，該檔案包含必要的GDI函式。

• 將 SelectPalette 該 DLL 中的 和 RealizePalette 函式定義為外部。

• 從現有的影像檔案 SampImag.jpg 建立一張圖片（必須與範例程式碼檔案同資料夾），並將圖片繪製到螢幕上。

• 建立內部指標型態變數，並將其值設定為 Graphics 物件的 handle，以及目前 Windows 的半色調調色盤。

• 選擇並實現半色調調色盤。

• 使用參數 hdc 建立一個新的圖形物件。

• 再畫一次那幅畫。

• 將 handle 釋放到裝置上下文中。

結果是兩個範例影像的渲染圖：一個是 16 位元調色盤，另一個是 8 位元調色盤。

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

備註

此 GetHalftonePalette 方法的目的是使 GDI+ 在顯示使用 8 位元每像素時，能產生更高品質的半色調。 若要使用半色調調色盤顯示影像，請使用以下程序。