WTL基础： 显示图片(JPG, BMP, PNG, TIF等)

         使用ATL 的Cimage类，图片文件大掉入和显示，变的十分简单。

        具体做法是，在stdafx.h 中包含头文件， #include <atlimage.h>

        定义一个CImage 对象， 如果要循环显示的话，定义成指针更简明。

       下面是一个完整的显示图片的控件代码。如果需要显示更多种类的图片，定义一下即可。

       

#pragma once#include "stdafx.h"enum { SOURCE_DIRECTORY, SOURCE_TEXT, SOURCE_DATA, SOURCE_BMP,  SOURCE_PNG, SOURCE_JPG,SOURCE_KNOWN };class CFileObjLooker : public CWindowImpl<CFileObjLooker, CStatic>,public COwnerDraw<CFileObjLooker>{protected:TCHARm_curSrcFile[MAX_PATH];CImage*m_pImage;UINT    m_nType;// 资源目标类型public:CFileObjLooker(void): m_pImage(NULL){memset( m_curSrcFile, 0, sizeof(m_curSrcFile));}~CFileObjLooker(){if(!m_pImage){delete m_pImage;m_pImage = NULL;}}void SetSourceFile(LPCTSTR tempPath){m_nType = SOURCE_KNOWN;lstrcpy( m_curSrcFile, tempPath);if(::PathIsDirectory(m_curSrcFile)){m_nType = SOURCE_DIRECTORY;return;}LPCTSTR pExt = ::PathFindExtension(m_curSrcFile);if(pExt){CString strExt = pExt;strExt.MakeLower();if(strExt == _T(".txt"))m_nType = SOURCE_TEXT;else if(strExt == _T(".dat"))m_nType = SOURCE_DATA;else if(strExt == _T(".bmp"))m_nType = SOURCE_BMP;else if(strExt == _T(".jpg"))m_nType = SOURCE_JPG;else if(strExt == _T(".png"))m_nType = SOURCE_PNG;}if(m_nType >= SOURCE_BMP && m_nType <= SOURCE_JPG){if(!m_pImage)delete m_pImage;m_pImage = new CImage();m_pImage->Load(m_curSrcFile);}this->Invalidate();}void DrawToCenter(CDCHandle dc,  LPCRECT lpRect ){if(!m_pImage)return;RECT rect, rect1;int boxWidth = lpRect->right - lpRect->left;int boxHeight = lpRect->bottom - lpRect->top;int imgWidth = m_pImage->GetWidth();int imgHeight = m_pImage->GetHeight();::SetRect( &rect, 0,0, imgWidth, imgHeight);if( boxWidth >= imgWidth &&  boxHeight >= m_pImage->GetHeight()){::OffsetRect( &rect, (boxWidth -imgWidth)/2, (boxHeight -imgHeight)/2);m_pImage->Draw( dc.m_hDC, rect);return;}FLOAT xScale = (FLOAT)imgWidth/boxWidth;FLOAT yScale = (FLOAT)imgHeight/boxHeight;FLOAT maxScale = max(xScale, yScale);imgWidth  =  (int)((FLOAT)imgWidth/maxScale);imgHeight =  (int)((FLOAT)imgHeight/maxScale);::SetRect( &rect1, 0,0, imgWidth, imgHeight);::OffsetRect( &rect1, (boxWidth -imgWidth)/2, (boxHeight -imgHeight)/2);dc.SetStretchBltMode(COLORONCOLOR);//SetStretchBltMode（hdc,HALFTONE）；//SetStretchBltMode(COLORONCOLOR)m_pImage->StretchBlt( dc.m_hDC, rect1, rect); }    BEGIN_MSG_MAP(CFileObjLooker)MESSAGE_HANDLER(WM_ERASEBKGND, OnEraseBkgnd)CHAIN_MSG_MAP_ALT( COwnerDraw<CFileObjLooker>,1 )DEFAULT_REFLECTION_HANDLER()    END_MSG_MAP()public:LRESULT OnEraseBkgnd(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& /*bHandled*/){return 1;}void DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct  ){CDCHandle dc = lpDrawItemStruct->hDC;RECT rcItem = lpDrawItemStruct->rcItem;dc.FillRect( &rcItem, 21);if(m_nType >= SOURCE_BMP && m_nType <= SOURCE_JPG){DrawToCenter(dc, &rcItem);}else{dc.MoveTo( rcItem.left, rcItem.top);dc.LineTo(rcItem.right, rcItem.bottom);}}};

当使用StretchBlt 函数显示缩小的图片的时候， 显示会很奇怪。 这时候需要设置模式。就是下面这行:

dc.SetStretchBltMode(COLORONCOLOR);

 要使用上面的控件， 在对话框上拉一个Picture控件， 设置为自绘模式，然后再对话框里面定义一个变量。

private: CFileTree m_tree; CFileObjLooker m_objFrame;    // 就是它了。

然后在 OnInitDialog 对这个变量进行子类化， 

m_objFrame.SubclassWindow(this->GetDlgItem(IDC_OBJFRM));

最后再提醒一下，要在对话框的消息映射模板最后添加消息反射。

// 添加消息反射, ObjectDispREFLECT_NOTIFICATIONS()END_MSG_MAP()

没有更多的事情需要做了。