delphi – 如何使用DrawThemeBackground绘制时,从右到左(RTL)方

发布时间：2020-12-15 09:18:20 所属栏目：大数据来源：网络整理

导读：我正在尝试从右到左绘制Explorer :: Treeview类的ttGlyphClosed元素(就像BiDiMode是bdLeftToRight时那样).我有一个问题,我不知道如何使我的屏幕外位图透明.位图的背景始终为白色. 我正在使用以下代码来镜像图像： procedure TForm5.FormPaint(Sender: TObjec

我正在尝试从右到左绘制Explorer :: Treeview类的ttGlyphClosed元素(就像BiDiMode是bdLeftToRight时那样).我有一个问题,我不知道如何使我的屏幕外位图透明.位图的背景始终为白色.

我正在使用以下代码来镜像图像：

procedure TForm5.FormPaint(Sender: TObject);
var
  bm: TBitmap;
  ARect: TRect;
  Details: TThemedElementDetails;
begin    
  if ExplorerTreeviewhTheme = 0 then
    ExplorerTreeviewhTheme := OpenThemeData(0,'Explorer::Treeview');

  ARect := Rect(20,20,40,40);
  Details := ThemeServices.GetElementDetails(ttGlyphClosed);
  DrawThemeBackground(ExplorerTreeviewhTheme,Canvas.Handle,Details.Part,Details.State,ARect,nil); //Ok

  bm := TBitmap.Create;
  try
    bm.Width := 20;
    bm.Height := 20;

    ARect := Rect(00,00,20);
    DrawThemeBackground(ExplorerTreeviewhTheme,bm.Canvas.Handle,nil);

    // rendered result has white background
    Canvas.Draw(60,10,bm);    
    // rendered result is mirrored but has also white background
    StretchBlt(Canvas.Handle,100,-20,SRCCOPY);
  finally
    bm.Free;
  end;    
end;

问题是如何镜像DrawThemeBackground函数绘制的元素(用于RTL读取)或如何使用此函数进行RTL(从右到左)渲染？

解决方法

使用SetLayout作为TLama在他现在删除的答案中显示,在绘制之前切换画布的布局.

function SetLayout(hdc: HDC; dwLayout: DWORD): DWORD; stdcall;
  external 'gdi32' name 'SetLayout';

const
  LAYOUT_RTL = $00000001;

procedure TForm1.FormPaint(Sender: TObject);
var
  ExplorerTreeviewhTheme: HTHEME;
  Details: TThemedElementDetails;
  ARect: TRect;
  Size: TSize;
begin
  ExplorerTreeviewhTheme := OpenThemeData(Handle,'Explorer::Treeview');
  Details := ThemeServices.GetElementDetails(ttGlyphClosed);
  GetThemePartSize(ExplorerTreeviewhTheme,nil,TS_DRAW,Size);

  ARect := Rect(20,30,20 + Size.cx,30 + Size.cy);

  // normal layout
  DrawThemeBackground(ExplorerTreeviewhTheme,nil);

  // switched layout
  SetLayout(Canvas.Handle,LAYOUT_RTL);

  // calculate the rectangle for RTL as if it's in LTR
  OffsetRect(ARect,Size.cy); // align to the bottom of the first image so that we can see
  ARect.Left := ClientWidth - ARect.Left - Size.cx;
  ARect.Right := ARect.Left + Size.cx;

  DrawThemeBackground(ExplorerTreeviewhTheme,nil);

  // restore layout
  SetLayout(Canvas.Handle,0);
  CloseThemeData(ExplorerTreeviewhTheme);
end;

输出：

主题api绘制了一个6px宽的三角形,尺寸为16px(W7-aero).由于您无法知道图像在零件中的位置,因此无法更好地对齐它.

（编辑：李大同）

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