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
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