用VC开发缩略图功能

原贴地址： http://www.codeproject.com/listctrl/ThumbsViewer.asp#xx1195695xx

Thumbnails Viewer using ListCtrl

Download source files - 924 Kb Download demo project - 389 Kb

Introduction

There are several image libraries and sources currently available. So I made my mind up to make a free Image Viewer using a free image library, and I got many free demo programs. I think a good image viewer must be able to show thumbnail images in a selected directory. I found some sources showing thumbnails, but they didn't support several formats, only BMP files. This thumbnail viewer is based on CxImage, so if there is an image format supported by CxImage, this viewer also supports that format.

Implementation

I want to show you the core part in this article. How to make a CListCtrl, CImageList, and then how to load images and attach that image to an ImageList.

1. Creating CListCtrl and CImageList

I used a CListView instead of CListCtrl, but you know that CListView uses CListCtrl internally. So overriding Create(...) will make your icon view CListCtrl initially. And then on OnInitialUpdate(), make ImageList which can support 24 bit color images and attach to CListCtrl.

return CListView::Create(lpszClassName, _T("ListView"),   dwStyle|LVS_SHOWSELALWAYS|LVS_ALIGNTOP|LVS_ICON|LVS_SINGLESEL| LVS_AUTOARRANGE, rect, pParentWnd, nID, pContext); .... m_ImageListThumb.Create(THUMBNAIL_WIDTH, THUMBNAIL_HEIGHT, ILC_COLOR24, 0, 1);  ListCtrl.SetImageList(&m_ImageListThumb, LVSIL_NORMAL);

2. Load Images and Insert Items

Create a Compatible DC and a Bitmap Handle. Stretch a loaded image to the Bitmap Handle and then attach it to CBitmap. Finally, replace CBitmap with an image in the ImageList.

unsigned __stdcall CThumbViewerView::LoadThumbNail(LPVOID lpParam) {  CThumbViewerView* pView=(CThumbViewerView*)lpParam;  CThumbViewerDoc* pDoc=pView->GetDocument();  CListCtrl& ListCtrl=pView->GetListCtrl();  CImageList* pImgList=&pView->m_ImageListThumb;  // reset our image list  for(int i=0; i<pImgList->GetImageCount(); i++)   pImgList->Remove(i);   // remove all items from list view  ListCtrl.DeleteAllItems();  pImgList->SetImageCount(pDoc->m_vFileName.size());  char path[MAX_PATH];  vector<CString>::iterator iter;    // Set redraw to FALSE to avoid flickering during adding new items  ListCtrl.SetRedraw(FALSE);  int nIndex=0;  for(iter=pDoc->m_vFileName.begin(); iter!=pDoc->m_vFileName.end() && pView->m_bTerminate!=true; iter++, nIndex++)  { ListCtrl.InsertItem(nIndex, *iter, nIndex);  }  ListCtrl.SetRedraw(TRUE);  ListCtrl.Invalidate();  // Create Brushes for Border and BackGround  HBRUSH hBrushBorder=::CreateSolidBrush(RGB(192, 192, 192));  HBRUSH hBrushBk=::CreateSolidBrush(RGB(255, 255, 255));  // Border Size  RECT rcBorder;  rcBorder.left=rcBorder.top=0;  rcBorder.right=THUMBNAIL_WIDTH;  rcBorder.bottom=THUMBNAIL_HEIGHT;  const float fRatio=(float)THUMBNAIL_HEIGHT/THUMBNAIL_WIDTH;  int XDest, YDest, nDestWidth, nDestHeight;  nIndex=0;  for(iter=pDoc->m_vFileName.begin(); iter!=pDoc->m_vFileName.end() && pView->m_bTerminate!=true; iter++, nIndex++)  {   // Load Image File   sprintf(path, "%s//%s", pDoc->m_strCurrentDirectory, *iter);   int nImageType=pDoc->GetTypeFromFileName(path);   if(nImageType==CXIMAGE_FORMAT_UNKNOWN)    continue;   CxImage image(path, nImageType);   if(image.IsValid()==false)    continue;   // Calculate Rect to fit to canvas   const float fImgRatio=(float)image.GetHeight()/image.GetWidth();   if(fImgRatio > fRatio)   {    nDestWidth=THUMBNAIL_HEIGHT/fImgRatio;    XDest=(THUMBNAIL_WIDTH-nDestWidth)/2;    YDest=0;    nDestHeight=THUMBNAIL_HEIGHT;   }   else   {    XDest=0;    nDestWidth=THUMBNAIL_WIDTH;    nDestHeight=THUMBNAIL_WIDTH*fImgRatio;    YDest=(THUMBNAIL_HEIGHT-nDestHeight)/2;   }   CClientDC cdc(pView);   HDC hDC=::CreateCompatibleDC(cdc.m_hDC);   HBITMAP bm = CreateCompatibleBitmap(cdc.m_hDC, THUMBNAIL_WIDTH, THUMBNAIL_HEIGHT);   HBITMAP pOldBitmapImage = (HBITMAP)SelectObject(hDC,bm);   // Draw Background   ::FillRect(hDC, &rcBorder, hBrushBk);   // Draw Image   image.Stretch(hDC, XDest, YDest, nDestWidth, nDestHeight);   // Draw Border   ::FrameRect(hDC, &rcBorder, hBrushBorder);   SelectObject(hDC, pOldBitmapImage);   // Attach to Bitmap and Replace image in CImageList   CBitmap bitmap;   bitmap.Attach(bm);   pImgList->Replace(nIndex, &bitmap, NULL);   // Redraw only a current item for removing flickering and fast speed.   ListCtrl.RedrawItems(nIndex, nIndex);   // Release used DC and Object   DeleteDC(hDC);   DeleteObject(bm);  }  DeleteObject(hBrushBorder);  DeleteObject(hBrushBk);  ListCtrl.Invalidate();  pView->m_bRunning=false;  pView->m_bTerminate=false;  _endthreadex( 0 );  return 0; }

Acknowledgment

You can download CxImage freely from here.

History

Ver. 1.0  15, Sep. 2003 First release. Ver. 1.1  24, Mar. 2005 Fixed crashing when changing a directory fast. Supports Unicode option using preprocessor _UNICODE.

About moah

Youngjin Kim lives in South Korea. I'm interested in every part of Computer Science, cause it has not been long time since graduate a University.But now I'm working and researching on Pattern Recognition. Using that trying to recognize a Handwriting Prints. Korean and Chinese are my interesting Research Part.

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