Knowledge Base

KB10337 - Mouse Wheel support in the TatukGIS Project.

Delphi supports the Mouse Wheel only as a focused control. So you can proceed by calling GIS_ViewerWND1.SetFocus. But better is to add OnMouseWheelXXX events on your form and redirect such events into the GIS_ViewerWND control.

For example, this code shows how to add zoom-in on a mouse wheel event:

procedure

TForm1.FormMouseWheelDown(Sender: TObject; Shift: TShiftState; MousePos: TPoint; var Handled: Boolean);

begin

GISMouseWheelDown( Sender, Shift, MousePos, Handled ) ;

end;



procedure TForm1.GISMouseWheelDown(Sender: TObject;

Shift: TShiftState; MousePos: TPoint; var Handled: Boolean);

var

  pt : TPoint ;

  ptg1 : TGIS_Point ;

  ptg2 : TGIS_Point ;

  delta : TGIS_Point ;

begin
with GIS do begin

  pt := ScreenToClient( MousePos ) ;

  if not PtInRect( ClientRect, pt ) then exit ; // not this window



  Handled := True ;

  if IsEmpty then exit ;



  // zoom and restore a proper map position

  ptg1 := ScreenToMap( ScreenToClient( MousePos ) ) ;

  Zoom := Zoom * 2 ;

  ptg2 := ScreenToMap( ScreenToClient( MousePos ) ) ;

  delta.X := ptg1.X - ptg2.X ;

  delta.Y := ptg1.Y - ptg2.Y ;

  Center := GisPoint( Center.X + delta.X, Center.Y + delta.Y ) ;

  Handled := True ;



  end ;

end;

Created: November 21, 2003, Modified: August 04, 2015