Ivor Horton's Beginning Visual C++ 2012

IDENTIFYING AN ELEMENT UNDER THE CURSOR

It will be a very simple mechanism for identifying the element under the mouse cursor. A sketch element will be under the cursor whenever the cursor is within the enclosing rectangle for the element. For this to be effective, Sketcher must track whether or not there is an element under the cursor at all times.

You can add code to the OnMouseMove() handler in the CSketcherView class to determine which element is under the cursor. This handler is called every time the mouse cursor moves, so all you have to do is add code to determine whether there’s an element under the current cursor position and set m_pSelected accordingly. The test for whether a particular element is under the cursor is simple: if the cursor position is inside the enclosing rectangle for an element, that element is under the cursor. Here’s how you can modify the OnMouseMove() handler to determine whether there’s an element under the cursor:

void CSketcherView::OnMouseMove(UINT nFlags, CPoint point)
{
  // Define a Device Context object for the view
  CClientDC aDC(this);              // DC is for this view
  OnPrepareDC(&aDC);                // Get origin adjusted
  aDC.DPtoLP(&point);               // Convert point to logical coordinates
 
  // Verify the left button is down and mouse messages captured
  if((nFlags & MK_LBUTTON) && (this == GetCapture()))
  {
    // Code as before...
  }
  else
  { // We are not creating an element, so select an element
    m_pSelected = GetDocument()->FindElement(point);
  }
}

The new code is one statement that ...