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POWhy doesn't the OnDraw suffice (in MFC, Scribble tutorial)
 

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  1. POWhy doesn't the OnDraw suffice (in MFC, Scribble tutorial)
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    <p>I'm making the Scribble tutorial to learn MFC and there's this code on the MouseMove event:</p> <pre><code>void CScribbleView::OnMouseMove(UINT nFlags, CPoint point) { // 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. // Add the new point to the current stroke m_pStrokeCur-&gt;m_pointArray.Add(point); CClientDC dc( this ); // Draw a line from the previous detected point in the mouse // drag to the current point. CPen* pOldPen = dc.SelectObject( GetDocument( )-&gt;GetCurrentPen( ) ); dc.MoveTo( m_ptPrev ); dc.LineTo( point ); dc.SelectObject( pOldPen ); m_ptPrev = point; CView::OnMouseMove(nFlags, point); } </code></pre> <p>And this one on the draw function of the stroke (which is called by the OnDraw of the view):</p> <pre><code>BOOL CStroke::DrawStroke( CDC* pDC ) { CPen penStroke; if( !penStroke.CreatePen(PS_SOLID, m_nPenWidth, RGB(0,0,0))) return FALSE; CPen* pOldPen = pDC-&gt;SelectObject( &amp;penStroke ); pDC-&gt;MoveTo( m_pointArray[0] ); for( int i=1; i &lt; m_pointArray.GetSize(); i++ ) { pDC-&gt;LineTo( m_pointArray[i] ); } pDC-&gt;SelectObject( pOldPen ); return TRUE; } </code></pre> <p>I've checked this function is being called on every frame update. However, if I take away the drawing on the mouse move event, it won't happen anything, even though I'm registering all the strokes and the draw stroke function is being called. Only if I make changes to the window (like maximizing) will the then appear.If the function </p> <p>is being called, why doesn't it draw on the window? I'm trying to figure out the inner workings of MFC here, it's not a bug or anything.</p>
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    1. USwebdreamer
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      1. POWhy doesn't the OnDraw suffice (in MFC, Scribble tutorial)
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    1. COI'm guessing here, but it may have to do with the underlying GDI (Graphics Device Interface) of Windows. In general, to save processing power, it doesn't want to redraw everything every frame like you would in a 3D app, just areas of the screen that have changed. Something you're doing in MouseMove but not in DrawStroke is probably marking the surface as needing a redraw.
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      1. POWhy doesn't the OnDraw suffice (in MFC, Scribble tutorial)
      1. USNathan Monteleone
    2. COinner working on windows... not mfc. Have you take into account that the background is erased, before OnPaint is called?
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      1. POWhy doesn't the OnDraw suffice (in MFC, Scribble tutorial)
      1. USneagoegab
    3. COdraw on a memory bitmap in your MouseMove function, disable background painting to avoid flickering, and draw the memory bitmap onto DC when OnPaint is called. To force OnPaint to be called, use InavalidateRect, UpdateWindow...
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      1. POWhy doesn't the OnDraw suffice (in MFC, Scribble tutorial)
      1. USneagoegab
 

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