Canvas mit Handle auf Bitmap.Canvas

[jbg]

Du musst ein neues erzeugen und das Bitmap-Handle dort selektieren, damit in das Bitmap gezeichnet wird

Delphi-Quellcode:

type
  TSurfaceCanvas = class(TCanvas)
  private
    FBmp: TBitmap;
    FOldBitmapHandle: HBITMAP;
    FOldPaletteHandle: HPALETTE;
  protected
    procedure CreateHandle; override;
  public
    constructor Create(AWidth, AHeight: Integer);
    destructor Destroy; override;

    property Bitmap: TBitmap read FBmp;
  end;

{ TSurfaceCanvas }

constructor TSurfaceCanvas.Create(AWidth, AHeight: Integer);
begin
  Assert(AWidth * AHeight > 0);
  inherited Create;
  FBmp := TBitmap.Create;
  FBmp.Width := AWidth;
  FBmp.Height := AHeight;
end;

procedure TSurfaceCanvas.CreateHandle;
begin
  Handle := CreateCompatibleDC(0);
  FOldBitmapHandle := SelectObject(Handle, FBmp.Handle);
  if not FBmp.IgnorePalette then
  begin
    FOldPaletteHandle := SelectObject(Handle, FBmp.Palette);
    // RealizePalette(FBmp.Palette); FALSCH
    RealizePalette(Handle);  // RICHTIG
  end;
end;

destructor TSurfaceCanvas.Destroy;
var
  DC: HDC;
begin
  if Handle <> 0 then
  begin
    SelectObject(Handle, FOldBitmapHandle);
    if FOldPaletteHandle <> 0 then
      SelectObject(Handle, FOldPaletteHandle);
    DC := Handle;
    Handle := 0;
    DeleteDC(DC);
  end;
  FBmp.Free;
  inherited Destroy;
end;