handles.pas

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unit Handles;

{ TStretchHandles is a transparent control to implement runtime grab handles
  for Forms Designer-like projects.  It paints the handles on its own canvas,
  maintains a list of the controls it is supposed to manage, and traps mouse
  and keyboard events to move/resize itself and its child controls.  See the
  accompanying README file for more information.

  Distributed by the author as freeware, please do not sell.

  Anthony Scott
  CIS: 75567,3547                                                              }

{ Fix Bug : OnMouseUp Event When Mouse Right Button No Respond Bug }
{ Modify By Tom Lee [e-mail] 1996 OCT 1 }

interface

uses
  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,
  Forms, Menus, StdCtrls, Dialogs;
                                       { miscellaneous type declarations }
type
  TDragStyle = (dsMove, dsSizeTopLeft, dsSizeTopRight, dsSizeBottomLeft, dsSizeBottomRight,
                dsSizeTop, dsSizeLeft, dsSizeBottom, dsSizeRight);
  TForwardMessage = (fmMouseDown, fmMouseUp);
  GridValues = 1..32;
  EBadChild = class(Exception);
                                       { TStretchHandle component declaration }
type
  TStretchHandle = class(TCustomControl)
  private
    FDragOffset: TPoint;
    FDragStyle: TDragStyle;
    FDragging: boolean;
    FDragRect: TRect;
    FLocked: boolean;
    FPrimaryColor: TColor;
    FSecondaryColor: TColor;
    FGridX, FGridY: GridValues;
    FChildList: TList;
    procedure WMEraseBkgnd(var Message: TWMEraseBkgnd); message WM_ERASEBKGND;
    procedure WMGetDLGCode(var Message: TMessage); message WM_GETDLGCODE;
    procedure Rubberband(XPos, YPos: integer; ShowBox: boolean);
    procedure ForwardMessage(FwdMsg: TForwardMessage; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
    procedure SetPrimaryColor(Color: TColor);
    procedure SetSecondaryColor(Color: TColor);
    procedure SetGridState(Value: boolean);
    function GetGridState: boolean;
    function GetChildCount: integer;
    function GetChildControl(idx: integer): TControl;
    function GetModifiedRect(XPos, YPos: integer): TRect;
    function PointOverChild(P: TPoint): boolean;
    function XGridAdjust(X: integer): integer;
    function YGridAdjust(Y: integer): integer;
    function IsAttached: boolean;
  protected
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
    procedure MouseUp(Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
    procedure MouseMove(Shift: TShiftState; X, Y: Integer); override;
    procedure KeyDown(var key: Word; Shift: TShiftState); override;
    procedure CreateParams(var Params: TCreateParams); override;
    procedure Paint; override;
    property Canvas;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    procedure Attach(ChildControl: TControl);
    procedure Detach;
    procedure ReleaseChild(ChildControl: TControl);
    procedure SetBounds(ALeft, ATop, AWidth, AHeight: Integer); override;
    procedure BringToFront;
    procedure SendToBack;
    procedure SetColors(Color1, Color2: TColor);
    function IndexOf(ChildControl: TControl): integer;
                                       { new run-time only properties }
    property Attached: boolean read IsAttached;
    property ChildCount: integer read GetChildCount;
    property Children[idx: integer]: TControl read GetChildControl;
  published
                                       { new properties }
    property Color: TColor read FPrimaryColor write SetPrimaryColor default clBlack;
    property SecondaryColor: TColor read FSecondaryColor write SetSecondaryColor default clGray;
    property Locked: boolean read FLocked write FLocked default False;
    property GridX: GridValues read FGridX write FGridX default 8;
    property GridY: GridValues read FGridY write FGridY default 8;
    property SnapToGrid: boolean read GetGridState write SetGridState default False;
                                       { inherited properties }
    property DragCursor;
    property Enabled;
    property Hint;
    property ParentShowHint;
    property PopupMenu;
    property ShowHint;
    property Visible;
                                       { defined events }
    property OnClick;
    property OnDblClick;
    property OnMouseDown;
    property OnMouseMove;
    property OnMouseUp;
    property OnKeyDown;
    property OnKeyUp;
    property OnKeyPress;
  end;

procedure Register;
function MinInt(a, b: integer): integer;
function MaxInt(a, b: integer): integer;

implementation

procedure Register;
begin
                                       { add the component to the 'Samples' tab }
  RegisterComponents('J_STD', [TStretchHandle]);

end;

constructor TStretchHandle.Create(AOwner: TComponent);
begin

  inherited Create(AOwner);
                                       { create storage for child objects }
  FChildList := TList.Create;
                                       { initialize default properties }
  Width := 24;
  Height := 24;
  FPrimaryColor := clBlack;
  FSecondaryColor := clGray;
                                       { a value of 1 is used to effectively disable the snap-to grid }
  FGridX := 1;
  FGridY := 1;
                                       { doesn't do anything until it is Attached to something else }
  Enabled := False;
  Visible := False;

end;

destructor TStretchHandle.Destroy;
begin
                                       { tidy up carefully }                                                                
  FChildList.Free;
  inherited Destroy;

end;

procedure TStretchHandle.CreateParams(var Params: TCreateParams);
begin
                                       { set default Params values }
  inherited CreateParams(Params);
                                       { then add transparency; ensures correct repaint order }
  Params.ExStyle := Params.ExStyle + WS_EX_TRANSPARENT;

end;

procedure TStretchHandle.WMGetDLGCode(var Message: TMessage);
begin
                                       { get arrow key press events }
  Message.Result := DLGC_WANTARROWS;

end;

procedure TStretchHandle.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
                                       { completely fake erase, don't call inherited, don't collect $200 }
  Message.Result := 1;

end;

procedure TStretchHandle.Attach(ChildControl: TControl);
var
  L, T, W, H: integer;
begin
                                       { definitely not allowed! }
  if ChildControl is TForm then
    raise EBadChild.Create('Handles can not be attached to a Form!');
                                       { add child component to unique list managed by TStretchHandle }
  if (ChildControl <> nil) and (FChildList.IndexOf(TObject(ChildControl)) = -1) then
    begin
                                       { make sure new child's Parent matches siblings }
      if (FChildList.Count > 0) and (ChildControl.Parent <> Parent) then
        Detach;
                                       { initialize when first child is attached }
      if FChildList.Count = 0 then
        begin
          Parent := ChildControl.Parent;
                                       { only make it visible now, to avoid color flashing, & accept events }
          FDragRect := Rect(0, 0, 0, 0);
          Enabled := True;
          Visible := True;
          inherited SetBounds(ChildControl.Left - 2, ChildControl.Top - 2, ChildControl.Width + 5, ChildControl.Height + 5);

        end
      else
        begin
                                       { set size to bound all children, plus room for handles }
          L := MinInt(Left, ChildControl.Left - 2);
          T := MinInt(Top, ChildControl.Top - 2);
          W := Maxint(Left + Width - 3, ChildControl.Left + ChildControl.Width) - L + 3;
          H := Maxint(Top + Height - 3, ChildControl.Top + ChildControl.Height) - T + 3;
          inherited SetBounds(L, T, W, H);

        end;
                                       { add to list of active Children }
      FChildList.Add(TObject(ChildControl));
                                       { re-set DragStyle }
      FDragStyle := dsMove;
                                       { use old BringToFront so as not to change Child's Z-order }
      if not (csDesigning in ComponentState) then
        begin
          inherited BringToFront;
                                       { allow us to get Mouse events immediately! }
          SetCapture(Handle);
                                       { get keyboard events }
          if Visible and Enabled then
            SetFocus;
        end;

    end;

end;

procedure TStretchHandle.Detach;
begin
                                       { remove all Child components from list }
  if FChildList.Count > 0 then
    with FChildList do
      repeat
        Delete(0);
      until Count = 0;
                                       { disable & hide StretchHandle }
  FLocked := False;
  Width := 24;
  Height := 24;
  Enabled := False;
  Visible := False;
  Parent := nil;
  FDragRect := Rect(0, 0, 0, 0);

end;

procedure TStretchHandle.ReleaseChild(ChildControl: TControl);
var
  idx, L, T, W, H: integer;
  AControl: TControl;
begin
                                       { delete the Child if it exists in the list }
  idx := FChildList.IndexOf(TObject(ChildControl));
  if (ChildControl <> nil) and (idx >= 0) then
    FChildList.Delete(idx);
                                       { disable & hide StretchHandle if no more children }
  if FChildList.Count = 0 then
    begin
      FLocked := False;
      Enabled := False;
      Visible := False;
      Parent := nil;
      FDragRect := Rect(0, 0, 0, 0);
    end
  else
    begin
                                       { set size to bound remaining children, plus room for handles }
      L := TControl(FChildList.Items[0]).Left - 2;
      T := TControl(FChildList.Items[0]).Top - 2;
      W := TControl(FChildList.Items[0]).Width + 3;
      H := TControl(FChildList.Items[0]).Height + 3;

      for idx := 0 to FChildList.Count - 1 do
        begin
          AControl := TControl(FChildList.Items[idx]);
          L := MinInt(L, AControl.Left - 2);
          T := MinInt(T, AControl.Top - 2);
          W := Maxint(L + W - 3, AControl.Left + AControl.Width) - L + 3;
          H := Maxint(T + H - 3, AControl.Top + AControl.Height) - T + 3;
        end;

      inherited SetBounds(L, T, W, H);

    end;

end;

function TStretchHandle.IndexOf(ChildControl: TControl): integer;
begin
                                       { simply pass on the result... }
  Result := FChildList.IndexOf(TObject(ChildControl));

end;

procedure TStretchHandle.BringToFront;
var
  i: integer;
begin
                                       { do nothing if not Attached }
  if Attached and not Locked then
    begin
                                       { take care of Children first, in Attach order }
      for i := 0 to FChildList.Count - 1 do
        begin
          TControl(FChildList[i]).BringToFront;
        end;
                                       { make sure keyboard focus is restored }
      inherited BringToFront;
      if Visible and Enabled then
        SetFocus;
    end;

end;

procedure TStretchHandle.SendToBack;
var
  i: integer;
begin
                                       { do nothing if not Attached }
  if Attached and not Locked then
    begin
                                       { take care of Children first, in Attach order }
      for i := 0 to FChildList.Count - 1 do
        begin
          TControl(FChildList[i]).SendToBack;