Draw While the Mouse Button Is Down

Between the time that the mouse button goes down and the time that it’s released, Scribble tracks the mouse and draws a trace of its movements in the view. OnMouseMove is called as the user moves the mouse while drawing the current stroke. The function connects the latest mouse ___location with its previous ___location and saves the new ___location as the previous point for the next time the function is called. To do the drawing, OnMouseMove constructs a local CClientDC object used to draw in the window’s client area.

To add code for OnMouseMove

1. Using WizardBar, jump to CScribbleView’s member function OnMouseMove in ScribbleView.cpp.

2. Replace the //TODO comments and code with the code shown here:

   // Mouse movement is interesting in the Scribble application
   // only if the user is currently drawing a new stroke by
   // dragging the captured mouse.
   
   if( GetCapture( ) != this )
   return;        // If this window (view) didn't capture the
   // mouse, the user isn't drawing in this window.
   
   CClientDC dc( this );
   
   m_pStrokeCur->m_pointArray.Add(point);
   
   // Draw a line from the previous detected point in the mouse
   // drag to the current point.
   CPen* pOldPen =
   dc.SelectObject( GetDocument( )->GetCurrentPen( ) );
      dc.MoveTo( m_ptPrev );
      dc.LineTo( point );
      dc.SelectObject( pOldPen );
      m_ptPrev = point;
      return;
   

In the Scribble application, OnLButtonDown, OnMouseMove, and OnLButtonUp handle the three phases of mouse drawing: beginning to track the mouse, tracking the mouse and connecting points, and ending mouse tracking.