delphimousedragmovewindow

Move borderless form with right mouse button in Delphi


I have this code from the internet to drag a borderless form by holding the Left mouse button down:

procedure TForm6.Image1MouseDown(Sender: TObject; Button: TMouseButton;Shift: TShiftState;X,Y: Integer);
const
  SC_DRAGMOVE = $F012;
begin
  if Button = mbLeft then
  begin
    ReleaseCapture;
    Perform(WM_SYSCOMMAND, SC_DRAGMOVE, 0);
  end;
end;

It works fine but I need to drag by Right mouse button. Which parameter must be changed for this?


Solution

  • How to move window by right mouse button using C++? has a solution which handles the dragging itself, instead of letting Windows do it. Projecting that work from MFC needs one to know what Delphi's Forms already handle, instead of overly calling WinApi functions.

    One major issue is to incorporate a window's caption height, which can rely on multiple factors. In my example I used a normal one for a sizable window and it works as expected using Windows 7 without any theme (looks like Windows 95). Having no caption, or having a tool window, or having no border, or having a window which can't be sized needs the calls to GetSystemMetrics() adjusted.

    I incorporated both: dragging by left mouse button and by right mouse button. Although I encourage still displaying a potential context menu at the end of the dragging (like the Explorer does so for dragging files), because it's still a right mouse button and every user expects a popup menu for that click.

    My example also works for both: bound to either a TWinControl or to the TForm itself.

    unit Unit1;
    
    interface
    
    uses
      Windows, Messages, Classes, Controls, Forms, ExtCtrls;
    
    const
      SC_DRAGMOVE=         SC_MOVE or $0002;  // The four low-order bits of the wParam parameter are used internally by the system
      SM_CXPADDEDBORDER=   92;
    
    type
      TForm1= class( TForm )
        Panel1: TPanel;
        procedure Panel1MouseDown( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer );
        procedure FormMouseMove( Sender: TObject; Shift: TShiftState; X, Y: Integer );
        procedure FormMouseUp( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer );
      private
        vStart: TPoint;
      end;
    
    var
      Form1: TForm1;
    
    implementation
    
    {$R *.dfm}
    
    // Mouse button is pressed down and held
    procedure TForm1.Panel1MouseDown( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer );
    begin
      case Button of
        mbLeft: begin  // Dragging through left mouse button
          ReleaseCapture();  // Restore normal mouse input processing; self.MouseCapture is already FALSE at this point
          self.Perform( WM_SYSCOMMAND, SC_DRAGMOVE, 0 );  // Handles all the rest of dragging the window
        end;
    
        mbRight: begin  // Through right mouse button
          GetCursorPos( self.vStart );  // Remember position on form, relative to screen
          self.vStart:= self.ScreenToClient( self.vStart );
          Inc( self.vStart.Y, GetSystemMetrics( SM_CYCAPTION )  // Window title height
                            + GetSystemMetrics( SM_CXPADDEDBORDER )  // Width of potential border padding
                            + GetSystemMetrics( SM_CYSIZEFRAME )  // Height of a potential window border when sizable; SM_CYEDGE is not enough
          );
    
          self.MouseCapture:= TRUE;  // WinApi: SetCapture( Handle )
        end;
      end;
    end;
    
    // Mouse is moved, unrelated to button status; must be handled by form, not panel
    procedure TForm1.FormMouseMove( Sender: TObject; Shift: TShiftState; X, Y: Integer );
    var
      pt: TPoint;
    begin
      if self.MouseCapture then begin  // WinApi: GetCapture()= Handle
        GetCursorPos( pt );  // Position on desktop
    
        Dec( pt.X, self.vStart.X );  // Subtract relative starting position
        Dec( pt.Y, self.vStart.Y );
    
        MoveWindow( self.Handle, pt.X, pt.Y, self.Width, self.Height, TRUE );  // Reposition window by horizontal and vertical deltas
      end;
    end;
    
    // Mouse button is released; must be handled by form, not panel
    procedure TForm1.FormMouseUp( Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer );
    begin
      if Button= mbRight then self.MouseCapture:= FALSE;  // End dragging
    end;
    

    Note that initiating the dragging is bound to the control's OnMouseDown event, but handling and ending the dragging must be bound to the form's events:

    object Form1: TForm1
      OnMouseMove = FormMouseMove
      OnMouseUp = FormMouseUp
      object Panel1: TPanel
        OnMouseDown = Panel1MouseDown
      end
    end