MFC drawing a line

Question

I need help with making a certain MFC program. I need to make a program that will draw a line in the following way: the user chooses the starting point by left clicking, and the final point by left clicking the second time, after which the points are connected and the line is drawn. I've managed to get the coordinates of the first one with this:

void CsemView::OnLButtonDown(UINT nFlags, CPoint point)
{
    CsemDoc* pDoc= GetDocument();
    // TODO: Add your message handler code here and/or call default 
    pDoc->a_pos=point;
    Invalidate();
    CView::OnLButtonDown(nFlags, point);
}

The problem is, i don't know how to get the coordinates of the second one with the second left click. I've managed to do it by using the on double left click function( and putting pDoc->b_pos=point; in it), but that's not really what I was supposed to do. (I was putting in the coordinates of the first one into MoveTo and the second one into LineTo). I would appreciate if someone could help me (I'm suspecting there's perhaps a different, simpler way of doing this). Thanks in advance.

Lines are usually drawn by starting a point on button down and then ending a point and the line on button up, then invalidating and then in OnDraw or OnPaint, drawing the line from those two points. Are you sure you want two button downs in succession to do this? — Paul Sasik

Emilio Garavaglia Emilio Garavaglia · Accepted Answer · 2013-01-12T21:14:56

If you want to get two results from a same event, you have to keep a state variable to track wht click is it.

On other words, your CsemDoc should have an a_pos and b_pos members, and CsemView a bool is_b, initialized as false.

The OnLButtonDow method should: be something like

if(!is_b)
{ set the a_pos; is_b = true; }
else
{ set the b_pos; is_b = false; invalidate the draw; }

MFC drawing a line

2 Answers