Q&A - Question

I have 3 types of shp files: line, points and polygon and there are several of them in TGIS_ViewerWnd.

When I zoom in or zoom out with the mouse TGIS_ViewerWnd works slowly.

For example, if I immediately zoom in or zoom out it slows down.

This my codes

it is for zoom in

void __fastcall TForm1::GISMouseWheelUp(TObject *Sender, TShiftState Shift, TPoint &MousePos,
          bool &Handled)
{   // zoom +
GIS->Lock();
    GIS->Zoom = GIS->Zoom * 1.2 ;
GIS->Unlock();
}


and it is for zoom out

void __fastcall TForm1::GISMouseWheelDown(TObject *Sender, TShiftState Shift, TPoint &MousePos,
          bool &Handled)
{ // zoom -
GIS->Lock();
    GIS->Zoom = GIS->Zoom / 1.2 ;
GIS->Unlock();
}

Now my question is what can I do so that when I zoom in or zoom out the scale it does not slow down?

void __fastcall TForm1::GISMouseWheelDown(TObject *Sender,
      TShiftState Shift, TPoint &MousePos, bool &Handled)
{
  TPoint  pt;

  if ( GIS->IsEmpty ) return ;

  pt = GIS->ScreenToClient( MousePos ) ;

  GIS->ZoomBy( 5./4., pt.x, pt.y );
  Handled = true ;
}

void __fastcall TForm1::GISMouseWheelUp(TObject *Sender, TShiftState Shift,
      TPoint &MousePos, bool &Handled)
{
  TPoint  pt;

  if ( GIS->IsEmpty ) return ;

  pt = GIS->ScreenToClient( MousePos ) ;

  GIS->ZoomBy( 4./5., pt.x, pt.y );
  Handled = true ;
}