unit CoolHint;

interface

uses
  Windows, Classes, Controls, Forms, Messages, Graphics;

type
  TddgHintWindow = class(THintWindow)
  private
    FRegion: THandle;
    procedure FreeCurrentRegion;
  public
    destructor Destroy; override;
    procedure ActivateHint(Rect: TRect; const AHint: string); override;
    procedure Paint; override;
    procedure CreateParams(var Params: TCreateParams); override;
end;

implementation

destructor TddgHintWindow.Destroy;
begin
  FreeCurrentRegion;
  inherited;
  Destroy;
end;

procedure TddgHintWindow.CreateParams(var Params: TCreateParams);
{ We need to remove the border created on the Windows API-level }
{ when the window is created. }
begin
  inherited; // ???
  CreateParams(Params);
  Params.Style := Params.Style and not ws_Border; // remove border
end;

procedure TddgHintWindow.FreeCurrentRegion;
{ Regions, like other API objects, should be freed when you are }
{ through using them. Note, however, that you cannot delete a }
{ region which is currently set in a window, so this method sets }
{ the window region to 0 before deleting the region object. }
begin
  if FRegion <> 0 then // if Region is alive...
  begin
    SetWindowRgn(Handle, 0, True); // set win region to 0
    DeleteObject(FRegion); // kill the region
    FRegion := 0; // zero out field
  end;
end;

procedure TddgHintWindow.ActivateHint(Rect: TRect; const AHint: string);
{ Called when the hint is activated by putting the mouse pointer }
{ above a control. }
begin
  with Rect do
    Right := Right + Canvas.TextWidth('WWWW'); // add some slop
  BoundsRect := Rect;
  FreeCurrentRegion;
  with BoundsRect do
    { Create a round rectangular region to display the hint window }
    FRegion := CreateRoundRectRgn(0, 0, Width, Height, Width, Height);
  if FRegion <> 0 then
    SetWindowRgn(Handle, FRegion, True); // set win region
  inherited;
  ActivateHint(Rect, AHint); // call inherited
end;

procedure TddgHintWindow.Paint;
{ This method gets called by the WM_PAINT handler. It is }
{ responsible for painting the hint window. }
var
  R: TRect;
begin
  R := ClientRect; // get bounding rectangle
  Inc(R.Left, 1); // move left side slightly
  Canvas.Font.Color := clInfoText; // set to proper color
  { paint string in the center of the round rect }
  DrawText(Canvas.Handle, PChar(Caption), Length(Caption), R, DT_NOPREFIX or DT_WORDBREAK or DT_CENTER or DT_VCENTER);
end;

var
  OldHintClass: THintWindowClass;

function SetNewHintClass(AClass: THintWindowClass): THintWindowClass;
var
  DoShowHint: Boolean;
begin
  Result := HintWindowClass; // return value is old hint window
  DoShowHint := Application.ShowHint;
  if DoShowHint then
    Application.ShowHint := False; // destroy old hint window
  HintWindowClass := AClass; // assign new hint window
  if DoShowHint then
    Application.ShowHint := True; // create new hint window
end;

initialization
  OldHintClass := SetNewHintClass(TddgHintWindow);

finalization
  SetNewHintClass(OldHintClass);

end.