形式 – 圆形与系统阴影

type
TForm1 = class(TForm)
  procedure FormCreate(Sender: TObject);
private
  procedure CreateFlatRoundRgn;
protected
  procedure CreateParams(var Params: TCreateParams); override;
public
end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure ExcludeRectRgn(var Rgn: HRGN; LeftRect,TopRect,RightRect,BottomRect: Integer);
var
  RgnEx: HRGN;
begin
  RgnEx := CreateRectRgn(LeftRect,BottomRect);
  CombineRgn(Rgn,Rgn,RgnEx,RGN_OR);
  DeleteObject(RgnEx);
end;

procedure TForm1.CreateFlatRoundRgn;
const
  CORNER_SIZE = 6;
var
  Rgn: HRGN;
begin
  with BoundsRect do
  begin
    Rgn := CreateRoundRectRgn(0,Right - Left + 1,Bottom - Top + 1,CORNER_SIZE,CORNER_SIZE);
    // exclude left-bottom corner
    ExcludeRectRgn(Rgn,Bottom - Top - CORNER_SIZE div 2,CORNER_SIZE div 2,Bottom - Top + 1);
    // exclude right-bottom corner
    ExcludeRectRgn(Rgn,Right - Left - CORNER_SIZE div 2,Right - Left,Bottom - Top);
  end;
  // the operating system owns the region,delete the Rgn only SetWindowRgn fails
  if SetWindowRgn(Handle,True) = 0 then
    DeleteObject(Rgn);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  BorderStyle := bsNone;
  CreateFlatRoundRgn;
end;

procedure TForm1.CreateParams(var Params: TCreateParams);
const
  CS_DROPSHADOW = $00020000;
begin
  inherited CreateParams(Params);
  with Params do
  begin
    Style := WS_POPUP;
    WindowClass.Style := WindowClass.Style or CS_DROPSHADOW;
  end;
end;

绘制自定义阴影的另一种方法是设置Window WS_EX_LAYERED并使用UpdateLayeredWindow

这是一个very good example的完成(来源是C,但很容易理解)

对于更复杂的形状,您可以在表单和Alpha Blend上使用PNG图像.

编辑：

调整WS_POPUP窗口大小是一个痛苦的世界…
你有几个选择：

>写一个WM_NCHITEST handler
>使用WM_Syscommand $F008调整大小(上面的链接)或$F012到move the Window.
>使用WS_EX_STATICEDGE and WS_SIZEBOX样式.

请注意,当您重新调整窗口区域(例如OnResize事件)时,需要重新创建窗口区域.