Graphics.GetHalftonePalette 方法

定義

命名空間:

System.Drawing

組件:

System.Drawing.Common.dll

套件:

System.Drawing.Common v9.0.0-rc.2.24474.1

來源:

Graphics.cs

取得目前 Windows 半色調調色盤的句柄。

public:
 static IntPtr GetHalftonePalette();

public static IntPtr GetHalftonePalette ();

static member GetHalftonePalette : unit -> nativeint

Public Shared Function GetHalftonePalette () As IntPtr

傳回

IntPtr

nativeint

指定調色盤句柄的內部指標。

範例

下列程式代碼範例是專為搭配 Windows Forms 使用而設計，而且需要 PaintEventArgse，這是 Paint 事件處理程式的參數。 程式代碼會執行下列動作：

• 定義 Windows DLL 檔案 gdi32.dll的互操作性 DllImportAttribute 屬性，其中包含必要的 GDI 函式。

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

• 從現有的圖像檔 SampImag.jpg 建立影像（必須與範例程式代碼檔案位於相同的資料夾中），並將影像繪製到畫面。

• 建立內部指標類型變數，並將其值分別設定為圖形物件的句柄和目前的 Windows 半色調調色盤。

• 選取並實現半色調調色盤。

• 使用 hdc 參數建立新的圖形物件。

• 再次繪製影像。

• 釋放裝置內容的句柄。

結果是範例影像的兩個轉譯：一個是16位調色盤，另一個是8位調色盤。

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

GetHalftonePalette 方法的目的是讓 GDI+ 在顯示器每圖元使用 8 位時產生更好的品質半色調。 若要使用半色調調色盤來顯示影像，請使用下列程式。