透明Panel

unit TransparentPanel;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls;
type
  TTransparentPanelClass = class(TPanel)
  private
    procedure SetParent(AParent: TWinControl); override;
    procedure WMEraseBkGnd(var Message: TWMEraseBkGnd); message WM_EraseBkGnd;
  protected
    procedure CreateParams(var Params: TCreateParams); override;
    procedure Paint; override;
  public
    constructor Create(AOwner: TComponent); override;
    procedure Invalidate; override;
  end;

implementation
constructor TTransparentPanelClass.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  ControlStyle := ControlStyle - [csOpaque];
end;

procedure TTransparentPanelClass.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  Params.ExStyle := Params.ExStyle or WS_EX_TRANSPARENT;
end;

//进行绘制
procedure TTransparentPanelClass.Paint;
begin
  Canvas.Brush.Style := bsClear;
  Canvas.Rectangle(0, 0, Width, Height);
  Canvas.TextOut(Width div 2, Height div 2, 'Transparent');
end;

procedure TTransparentPanelClass.WMEraseBkGnd(var Message: TWMEraseBkGnd);
begin
  Message.Result := 1;
end;

procedure TTransparentPanelClass.SetParent(AParent: TWinControl);
begin
  inherited SetParent(AParent);
  if Parent <> nil then
    SetWindowLong(Parent.Handle, GWL_STYLE, GetWindowLong
      (Parent.Handle, GWL_STYLE) and not WS_ClipChildren);
end;

procedure TTransparentPanelClass.Invalidate;
var
  oRect: TRect;
begin
  //重画
  oRect := BoundsRect;
  if (Parent <> nil) and Parent.HandleAllocated then
    InvalidateRect(Parent.Handle, @oRect, True)
  else
    inherited Invalidate;
end;

end.