Move or resize graphically a TControl object by using another objet that has all the necessary code.

The unit showed bellow is for the TControlHandler class.

TControlHandler can manipulate graphically any descendant of the TControl class. A TControl objet can be selected by the TControlHandler Control property : a border appears surrounding the control passed to this method as  reference. At run-time, you can then change its location or change its size with the mouse.
For example, in an application, create a TControlHandler at startup :
  FControlHandler := TControlHandler.Create(Self);
To manipulate a Button1 objet placed on the form, write the following instruction :
  FControlHandler.Control := Button1;
You can choose another control by assigning a new TControl's reference ; the previous one is deselected.


unit ControlHandler;

// Written by Bertrand Goetzmann (http://www.object-everywhere.com)

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, ExtCtrls, ComCtrls;

type
  TControlPoint = (pcTopLeft, pcTopRight, pcBottomLeft, pcBottomRight, pcOther);

  TControlHandler = class(TCustomControl)
  private
    Rgn: HRGN;
    R, R1: TRect;
    Pos: TPoint;
    Pt: TControlPoint;
    bDrag: Boolean;
  protected
    FControl: TControl;
    procedure SetRegion;
    function GetControlPoint(const Point: TPoint): TControlPoint;
    procedure Paint; override;
    procedure MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
    procedure MouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
    procedure MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    procedure SetControl(Control: TControl);
  published
    property Control: TControl read FControl write SetControl;
  end;

implementation

const
  LARGEUR = 5;


// Méthodes de TControlHandler

constructor TControlHandler.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  Parent := AOwner as TWinControl;

  Rgn := 0;
  bDrag := False;

  OnMouseDown := MouseDown;
  OnMouseMove := MouseMove;
  OnMouseUp := MouseUp;
end;

destructor TControlHandler.Destroy;
begin
  if Rgn <> 0 then
    DeleteObject(Rgn);
  inherited Destroy;
end;

function TControlHandler.GetControlPoint(const Point: TPoint): TControlPoint;
begin
  Result := pcOther;
  if PtInRect(Rect(0, 0, LARGEUR, LARGEUR), Point) then
    Result := pcTopLeft
  else if PtInRect(Rect(Width-LARGEUR, 0, Width, LARGEUR), Point) then
    Result := pcTopRight
  else if PtInRect(Rect(0, Height-LARGEUR, LARGEUR, Height), Point) then
    Result := pcBottomLeft
  else if PtInRect(Rect(Width-LARGEUR, Height-LARGEUR, Width, Height), Point) then
    Result := pcBottomRight;
end;

procedure TControlHandler.MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  Pos.x := X;
  Pos.y := Y;
  bDrag := True;

  R := Rect(FControl.Left, FControl.Top, FControl.Left + FControl.Width, FControl.Top + FControl.Height);
  R1 := Rect(FControl.Left, FControl.Top, FControl.Left + FControl.Width, FControl.Top + FControl.Height);

  Pt := GetControlPoint(Pos);

  Visible := False;
end;

procedure TControlHandler.MouseUp(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  Screen.Cursor := crDefault;
  bDrag := False;

  Control.Left := R.Left;
  Control.Top := R.Top;
  Control.Width := R.Right - R.Left;
  Control.Height := R.Bottom - R.Top;

  SetRegion;

  Visible := True;
end;

procedure TControlHandler.MouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);
begin
  case GetControlPoint(Point(X, Y)) of
    pcTopLeft :
        Cursor := crSizeNWSE;
    pcTopRight :
        Cursor := crSizeNESW;
    pcBottomLeft :
        Cursor := crSizeNESW;
    pcBottomRight :
        Cursor := crSizeNWSE;
    pcOther :
        Cursor := crDrag;
  end;

  if not bDrag then Exit;

  case Pt of
    pcTopLeft : begin
        R.Left := R1.Left + X - Pos.x;
        R.Top := R1.Top + Y - Pos.y;
      end;
    pcTopRight : begin
        R.Right := R1.Right + X - Pos.x;
        R.Top := R1.Top + Y - Pos.y;
      end;
    pcBottomLeft : begin
        R.Left := R1.Left + X - Pos.x;
        R.Bottom := R1.Bottom + Y - Pos.y;
      end;
    pcBottomRight : begin
        R.Right := R1.Right + X - Pos.x;
        R.Bottom := R1.Bottom + Y - Pos.y;
      end;
    pcOther : begin
        R.Left := R1.Left + X - Pos.x;
        R.Top := R1.Top + Y - Pos.y;
        R.Right := R1.Right + X - Pos.x;
        R.Bottom := R1.Bottom + Y - Pos.y;
      end;
  end;

  with FControl do
  begin
    Left := R.Left;
    Top := R.Top;
    Width := R.Right - R.Left;
    Height := R.Bottom - R.Top;
  end;
end;

procedure TControlHandler.SetRegion;
var
  Rgn1, Rgn2: HRGN;
begin
  if Rgn <> 0 then DeleteObject(Rgn);
  Visible := False;

  Left := Control.Left - LARGEUR;
  Top := Control.Top - LARGEUR;
  Width := Control.Width + 2*LARGEUR;
  Height := Control.Height + 2*LARGEUR;

  Rgn := CreateRectRgn(0, 0, Width, Height);
  Rgn1 := CreateRectRgn(0, 0, Width, Height);
  Rgn2 := CreateRectRgn(LARGEUR, LARGEUR, Control.Width + LARGEUR, Control.Height + LARGEUR);
  CombineRgn(Rgn, Rgn1, Rgn2, RGN_DIFF);
  DeleteObject(Rgn1);
  DeleteObject(Rgn2);
  SetWindowRgn(Handle, Rgn, True);

  Visible := True;
end;

procedure TControlHandler.SetControl(Control: TControl);
begin
  FControl := Control;
  SetRegion;
end;

procedure TControlHandler.Paint;
begin
  with Canvas do
  begin
    Brush.Color := clBlack;
    Brush.Style := bsBDiagonal;
    Rectangle(0, 0, Width, Height);

    // Dessiner les poignets
    Brush.Style := bsSolid;
    FillRect(Rect(0, 0, LARGEUR, LARGEUR));
    FillRect(Rect(Width-LARGEUR, 0, Width, LARGEUR));
    FillRect(Rect(0, Height-LARGEUR, LARGEUR, Height));
    FillRect(Rect(Width-LARGEUR, Height-LARGEUR, Width, Height));
  end;
end;

end.