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#define MAXZOOMIN    4        // Maximum zoom-in factor最大放大因子
#define PICKMARGIN  10        // Screen pixels apart for region zoom用于缩放区域的屏幕像素成组个数
/////////////////////////////////////////////////////////////////////////////
// CZoomView
IMPLEMENT_DYNCREATE(CZoomView, CScrollView)
/*---------------------------------------------------------------------------
FUNCTION: CZoomView
PURPOSE : Constructor for the CZoomView class 构造函数
---------------------------------------------------------------------------*/
CZoomView::CZoomView()
: CScrollView()
{
// Init zoom mode to nothing模式设置为空
m_zoomMode    = MODE_ZOOMOFF;
m_bCaptured   = FALSE;
m_zoomScale   = 1.0;>
m_ptDragRect.SetRectEmpty();
// Load the zoom cursor加载图标
m_hZoomCursor = ::LoadCursor(AfxGetInstanceHandle(), MAKEINTRESOURCE(IDC_ZOOMCURSOR));
// Default to centering on full fit默认屏幕居中
m_bCenter = TRUE;
} // CZoomView
/*---------------------------------------------------------------------------
FUNCTION: ~CZoomView
PURPOSE : Destructor for the CZoomView class 析构函数
---------------------------------------------------------------------------*/                    
CZoomView::~CZoomView()
{
// Clean up the cursors if they were loaded properly释放图标
if (m_hZoomCursor) DestroyCursor(m_hZoomCursor);
} // ~CZoomView
/////////////////////////////////////////////////////////////////////////////
// CZoomView overridden default CScrollView members
/////////////////////////////////////////////////////////////////////////////
/*---------------------------------------------------------------------------
FUNCTION: SetZoomSizes
PURPOSE : Set up the CZoomView class with the logical page size, and 以逻辑页面大小和滚动页/行单位来设置
scrolling page/line units.
This replaces CScrollView::SetScrollSizes.替换CScrollView::SetScrollSizes                    
---------------------------------------------------------------------------*/

void CZoomView::SetZoomSizes (
SIZE sizeTotal,
const SIZE& sizePage, // in logical units逻辑单位
const SIZE& sizeLine) // in logical units
{
// Set up the defaults设置为默认
ASSERT(sizeTotal.cx >= 0 && sizeTotal.cy >= 0);
m_nMapMode    = MM_ANISOTROPIC; // Need for arbitrary scaling需要服务于自由缩放
m_totalLog    = sizeTotal;//文档里的m_sizeDoc决定的大小
// Setup default Viewport extent to be conversion of Window extent
// into device units.设置默认的视口大小，使窗口大小以设备单位能够和视口大小转换
//BLOCK for DC DC代码块
CWindowDC dc(NULL);
dc.SetMapMode(m_nMapMode);
// total size总大小
m_totalDev = m_totalLog;
dc.LPtoDP((LPPOINT)&m_totalDev);
} // Release DC here
 // Save the origional Viewport Extent保存视口大小原来值
m_origTotalDev = m_totalDev;
// Save the origional scrollbar info - for CalcBars保存滚动信息原来值 -用于CalcBars
m_origPageDev = sizePage;//滚动用的页面大小
m_origLineDev = sizeLine;//滚动用的一行的大小
// Fugure out scroll bar info计算滚动条信息
CalcBars();
// Notify the class that the zoom scale was set通知类缩放比例设置好了
NotifyZoom();
} // SetZoomSizes
/*---------------------------------------------------------------------------
FUNCTION: OnPrepareDC
PURPOSE : Override of CScrollView for MM_ANISOTROPIC zoom mode MM_ANISOTROPIC模式设置
---------------------------------------------------------------------------*/
void CZoomView::OnPrepareDC (
CDC* pDC, 
CPrintInfo* pInfo)
{
#ifdef _DEBUG
if (m_nMapMode != MM_ANISOTROPIC) {
TRACE0("Error: must call SetZoomSizes() before painting zoom view\n");
ASSERT(FALSE);
return;
}
#endif //_DEBUG
ASSERT_VALID(pDC);
ASSERT(m_totalLog.cx >= 0 && m_totalLog.cy >= 0);
ASSERT(m_totalDev.cx >= 0 && m_totalDev.cx >= 0);
// Set the Mapping mode, and the window and viewport extents设置模式，窗口和视口大小
pDC->SetMapMode(m_nMapMode);
pDC->SetWindowExt(m_totalLog);   // in logical coordinates逻辑坐标单位
CPoint ptVpOrg;
if (!pDC->IsPrinting()) {//如果不是打印
//初始化时m_totalLog==m_totalDev，通过修改视口大小来实现缩放
pDC->SetViewportExt(m_totalDev); // in device  coordinates设备坐标单位
// by default shift viewport origin in negative direction of scroll默认把原点设置到滚动方向的反方向
ASSERT(pDC->GetWindowOrg() == CPoint(0,0));
ptVpOrg = -GetDeviceScrollPosition();
// Center full fit居中自适应
if (m_bCenter) {
CRect rect;
GetClientRect(&rect);
// if client area is larger than total device size,如果客户区比设备总大小大，
// override scroll positions to place origin such that覆盖滚动位置来设置原点位置，让输出居中到窗口
// output is centered in the window
if (m_totalDev.cx < rect.Width())
ptVpOrg.x = (rect.Width() - m_totalDev.cx) / 2;
if (m_totalDev.cy < rect.Height())
ptVpOrg.y = (rect.Height() - m_totalDev.cy) / 2;
}
} else {
// Special case for printing打印情况的处理
CSize  printSize;
printSize.cx = pDC->GetDeviceCaps(HORZRES);
printSize.cy = pDC->GetDeviceCaps(VERTRES);
// Maintain the origional ratio, setup origin shift维护原来比例，设置原点进行移动
PersistRatio(m_totalLog, printSize, ptVpOrg);
// Zoom completely out缩小
pDC->SetViewportExt(printSize);
}
// Set the new origin设置新的原点
pDC->SetViewportOrg(ptVpOrg);
// For default Printing behavior
CView::OnPrepareDC(pDC, pInfo);
} // OnPrepareDC