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<p>void CDrawView::OnDraw(CDC* pDC)</p>
<p>{</p>
<p>CDrawDoc* pDoc = GetDocument();</p>
<p>ASSERT_VALID(pDoc);</p>
<p><b> </b></p>
<b>
<p>// Get the invalidated rectangle of the view, or in the case</p>
<p>// of printing, the clipping region of the printer dc.</p>
<p>CRect rectClip;</p>
<p>CRect rectStroke;</p>
<p>pDC->GetClipBox(&rectClip);</p>
<p>pDC->LPtoDP(&rectClip);</p>
<p>rectClip.InflateRect(1, 1); // avoid rounding to nothing</p>
<p>// Note: CScrollView::OnPaint() will have already adjusted the</p>
<p>// viewport origin before calling OnDraw(), to reflect the</p>
<p>// currently scrolled position.</p>
<p>// The view delegates the drawing of individual strokes to</p>
<p>// CStroke::DrawStroke().</p>
<p>CTypedPtrList<CObList,CStroke*>& strokeList = pDoc->m_strokeList;</p>
<p>POSITION pos = strokeList.GetHeadPosition();</p>
<p>while (pos != NULL)</p>
<p>{</p>
<p>CStroke* pStroke = strokeList.GetNext(pos);</p>
<p>rectStroke = pStroke->GetBoundingRect();</p>
<p>pDC->LPtoDP(&rectStroke);</p>
<p>rectStroke.InflateRect(1, 1); // avoid rounding to nothing</p>
<p>if (!rectStroke.IntersectRect(&rectStroke, &rectClip))</p>
<p>continue;</p>
<p>pStroke->DrawStroke(pDC);</p>
<p>}</p>
</b>
<p>// TODO: add draw code for native data here</p>
<p>}</p>
<p>OnDraw首先調用GetClipBox取得當前被剪裁區域（無效矩形區域），它把矩形復制導GetClipBox的參數rectClip中。然后將rectClip的坐標由邏輯坐標轉換為設備坐標。為了防止該矩形太小而無法包圍其他內容，上下各放大一個單位。然后OnDraw遍歷筆劃鏈表中的所有筆劃，獲取它們的最小矩形，用IntersectRect看它是否與無效矩形相交。如果相交，說明筆劃的部分或全部落在無效矩形中，此時調用筆劃的DrawStroke方法畫出該筆劃。</p>
<p> <b>圖8-6</b>
根據包圍筆劃 的矩形是否與無效</p>
<p> 矩形相交
，判斷筆劃是否落入無效矩形中 </p>
<p> 為了獲得筆劃的最小包圍矩形，需要在結束筆劃時計算出包圍筆劃的最小矩形。因此為筆劃提供兩個方法：一個是FinishStroke()，用于在筆劃結束時計算最小矩形，見清單8.7。</p>
<p> <b>清單</b><b>8.7
CStroke::FinishStroke()成員函數</b></p>
<p>void CStroke::FinishStroke()</p>
<p>{</p>
<p>// Calculate the bounding rectangle. It's needed for smart</p>
<p>// repainting.</p>
<p>if (m_pointArray.GetSize()==0)</p>
<p>{</p>
<p>m_rectBounding.SetRectEmpty();</p>
<p>return;</p>
<p>}</p>
<p>CPoint pt = m_pointArray[0];</p>
<p>m_rectBounding = CRect(pt.x, pt.y, pt.x, pt.y);</p>
<p>for (int i=1; i < m_pointArray.GetSize(); i++)</p>
<p>{</p>
<p>// If the point lies outside of the accumulated bounding</p>
<p>// rectangle, then inflate the bounding rect to include it.</p>
<p>pt = m_pointArray[i];</p>
<p>m_rectBounding.left = min(m_rectBounding.left, pt.x);</p>
<p>m_rectBounding.right = max(m_rectBounding.right, pt.x);</p>
<p>m_rectBounding.top = max(m_rectBounding.top, pt.y);</p>
<p>m_rectBounding.bottom = min(m_rectBounding.bottom, pt.y);</p>
<p>}</p>
<p>// Add the pen width to the bounding rectangle. This is necessary</p>
<p>// to account for the width of the stroke when invalidating</p>
<p>// the screen.</p>
<p>m_rectBounding.InflateRect(CSize(m_nPenWidth, -(int)m_nPenWidth));</p>
<p>return;</p>
<p>}</p>
<p>另一個是DrawStroke()，用于繪制筆劃：</p>
<p>BOOL CStroke::DrawStroke(CDC* pDC)</p>
<p>{</p>
<p>CPen penStroke;</p>
<p>if (!penStroke.CreatePen(PS_SOLID, m_nPenWidth, RGB(0,0,0)))</p>
<p>return FALSE;</p>
<p>CPen* pOldPen = pDC->SelectObject(&penStroke);</p>
<p>pDC->MoveTo(m_pointArray[0]);</p>
<p>for (int i=1; i < m_pointArray.GetSize(); i++)</p>
<p>{</p>
<p>pDC->LineTo(m_pointArray[i]);</p>
<p>}</p>
<p>pDC->SelectObject(pOldPen);</p>
<p>return TRUE;</p>
<p>}</p>
<p>鼠標繪圖</p>
<p align="JUSTIFY"> 鼠標繪圖基本過程是：用戶按下鼠標左鍵時開始繪圖，在鼠標左鍵按下且移動過程中不斷畫線跟蹤鼠標位置，當松開鼠標左鍵結束繪圖。因此，需要處理三個消息：WM_LBUTTONDOWN、WM_MOUSEMOVE、WM_LBUTTONUP。用ClassWizard為上述三個消息生成消息處理函數，并在其中手工加入代碼，修改后的成員函數如下：</p>
<p align="JUSTIFY"> <b> </b></p>
<b>
<p align="JUSTIFY"> 清單8.8
鼠標消息處理函數OnLButtonDown()</p>
</b>
<p>void CDrawView::OnLButtonDown(UINT nFlags, CPoint point) </p>
<p>{</p>
<p>// TODO: Add your message handler code here and/or call default</p>
<p>// Pressing the mouse button in the view window starts a new stroke</p>
<p>// CScrollView changes the viewport origin and mapping mode.</p>
<p>// It's necessary to convert the point from device coordinates</p>
<p>// to logical coordinates, such as are stored in the document.</p>
<p>CClientDC dc(this);</p>
<p>OnPrepareDC(&dc);</p>
<p>dc.DPtoLP(&point);</p>
<p>m_pStrokeCur = GetDocument()->NewStroke();</p>
<p>// Add first point to the new stroke</p>
<p>m_pStrokeCur->m_pointArray.Add(point);</p>
<p>SetCapture(); // Capture the mouse until button up.</p>
<p>m_ptPrev = point; // Serves as the MoveTo() anchor point for the</p>
<p>// LineTo() the next point, as the user drags the</p>
<p>// mouse.</p>
<p>return;</p>
<p>}</p>
<p> </p>
<p> 在鼠標左鍵按下，首先獲得鼠標按下的位置坐標。由于它是設備坐標，因此先用DPToLP將它轉換為邏輯坐標。在此之前，要用OnPrepareDC()對視圖坐標原點進行調整。然后用CDrawDoc的NewStroke()成員函數創建一個筆劃對象，并將筆劃對象加入到筆劃鏈表中。然后，將當前點坐標加入道筆劃對象內部的點數組中。以后，當鼠標移動時，OnMouseMove就不斷修改該筆劃對象的內部數據成員（加入新的點到筆劃對象的數組中）。另外，為了用LineTo畫出線條，需要將當前鼠標位置保存到m_ptPrev中，以便出現一個新的點時，畫一條從m_ptPrev到新的點的直線。</p>
<p> 但是，由于用戶的鼠標可以在屏幕上任意移動。當鼠標移出窗口外時，窗口無法收到鼠標消息。此時，如果松開了鼠標左鍵，應用程序由于無法接受到該條消息而不會終止當前筆劃，這樣就造成了錯誤。如何避免這種情況發生呢？解決的辦法是要讓窗口在鼠標移出窗口外時仍然能接受到鼠標消息。幸好，Windows提供了一個API函數SetCapture()解決了這一問題。</p>
<p> CWnd::SetCapture()用于捕獲鼠標：無論鼠標光標位置在何處，都會將鼠標消息送給調用它的那一個窗口。在用完后，需要用ReleaseCapture()釋放窗口對鼠標的控制，否則其他窗口將無法接收到鼠標消息。這一工作當然最好在鼠標左鍵松開OnLButtonUp()時來做。</p>
<p> <b>清單</b><b>8.9
OnLButtonUp消息處理函數</b></p>
<p>void CDrawView::OnLButtonUp(UINT nFlags, CPoint point) </p>
<p>{</p>
<p>// TODO: Add your message handler code here and/or call default</p>
<p> </p>
<p>// Mouse button up is interesting in the draw application</p>
<p>// only if the user is currently drawing a new stroke by dragging</p>
<p>// the captured mouse.</p>
<p>if (GetCapture() != this)</p>
<p>return; // If this window (view) didn't capture the mouse,</p>
<p>// then the user isn't drawing in this window.</p>
<p>CDrawDoc* pDoc = GetDocument();</p>
<p>CClientDC dc(this);</p>
<p>// CScrollView changes the viewport origin and mapping mode.</p>
<p>// It's necessary to convert the point from device coordinates</p>
<p>// to logical coordinates, such as are stored in the document.</p>
<p>OnPrepareDC(&dc); // set up mapping mode and viewport origin</p>
<p>dc.DPtoLP(&point);</p>
<p>CPen* pOldPen = dc.SelectObject(pDoc->GetCurrentPen());</p>
<p>dc.MoveTo(m_ptPrev);</p>
<p>dc.LineTo(point);</p>
<p>dc.SelectObject(pOldPen);</p>
<p>m_pStrokeCur->m_pointArray.Add(point);</p>
<p>// Tell the stroke item that we're done adding points to it.</p>
<p>// This is so it can finish computing its bounding rectangle.</p>
<p>m_pStrokeCur->FinishStroke();</p>
<p>// Tell the other views that this stroke has been added</p>
<p>// so that they can invalidate this stroke's area in their</p>
<p>// client area.</p>
<p>pDoc->UpdateAllViews(this, 0L, m_pStrokeCur);</p>
<p>ReleaseCapture(); // Release the mouse capture established at</p>
<p>// the beginning of the mouse drag.</p>
<p>return;</p>
<p>}</p>
<p> </p>
<p> OnLButtonUp首先檢查鼠標是否被當前窗口所捕獲，如果不是則返回。然后畫出筆劃最后兩點之間的極短的直線段。接著，調用CStroke::FinishStroke()，請求CStroke對象計算它的最小矩形。然后調用pDoc->UpdateAllViews(this,
0L, m_pStrokeCur)通知其他視圖更新顯示。</p>
<p> 當一個視圖修改了文檔內容并更新顯示時，一般的其它的對應于同一文檔的視圖也需要相應更新，這通過調用文檔的成員函數UpdateAllViews完成。</p>
<blockquote>
<blockquote>
<p>void UpdateAllViews( CView* pSender, LPARAM lHint = 0L, CObject*
pHint = </p>
<p>NULL );</p>
</blockquote>
</blockquote>
<p> UpdateAllViews帶三個參數：pSender指向修改文檔的視圖。由于該視圖已經作了更新，所以不再需要更新。比如，在上面的例子中，OnLButtonUp已經繪制了視圖，因此不需要再次更新。如果為NULL，則文檔對應的所有視圖都被更新。</p>
<p> lHint和pHint包含了更新視圖時所需的附加信息。在本例中，其他視圖只需要重畫當前繪制中的筆劃，因此OnLButtonUp把當前筆劃指針傳給UpdateAllViews函數。該函數調用文檔所對應的除pSender外的所有視圖的OnUpdate函數，并將lHint和pHint傳給OnUpdate函數通知更新附加信息。</p>
<p> OnLButtonUp最后釋放對鼠標的控制，這樣別的應用程序窗口就可以獲得鼠標消息了。</p>
<p> 結合上面講到的知識，讀者不難自行理解下面的OnMouseMove函數。</p>
<p>void CDrawView::OnMouseMove(UINT nFlags, CPoint point) </p>
<p>{</p>
<p>// TODO: Add your message handler code here and/or call default</p>
<p>// Mouse movement is interesting in the Scribble application</p>
<p>// only if the user is currently drawing a new stroke by dragging</p>
<p>// the captured mouse.</p>
<p>if (GetCapture() != this)</p>
<p>return; // If this window (view) didn't capture the mouse,</p>
<p>// then the user isn't drawing in this window.</p>
<p>CClientDC dc(this);</p>
<p>// CScrollView changes the viewport origin and mapping mode.</p>
<p>// It's necessary to convert the point from device coordinates</p>
<p>// to logical coordinates, such as are stored in the document.</p>
<p>OnPrepareDC(&dc);</p>
<p>dc.DPtoLP(&point);</p>
<p>m_pStrokeCur->m_pointArray.Add(point);</p>
<p>// Draw a line from the previous detected point in the mouse</p>
<p>// drag to the current point.</p>
<p>CPen* pOldPen = dc.SelectObject(GetDocument()->GetCurrentPen());</p>
<p>dc.MoveTo(m_ptPrev);</p>
<p>dc.LineTo(point);</p>
<p>dc.SelectObject(pOldPen);</p>
<p>m_ptPrev = point;</p>
<p>return;</p>
<p>}</p>
<p>至此，繪圖程序的文檔、視圖全部設計完了，現在編譯運行程序。程序啟動后，在空白窗口中徒手繪圖，如圖8-7所示。</p>
<p align="center"> <img src="T8_7.gif" alt="T8_7.tif (267124 bytes)" width="470" height="335"></p>
<p align="center">圖8-7
多文檔繪圖程序窗口</p>
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