[OLE/GDI+] Save Thumbnail of a Web Page To File

Using the technique introduced here you can generate a thumbnail of a web page (or part of it) and save it to an image file.

IHTMLElementRender interface allows users to draw the content of an element (usually IHTMLElement) to a device context (DC). The Image class in GDI+ provides a uniform way to save the image as a file.

The code is quite simple and self-explanatory.

IWebBrowser2 *wb = NULL;
IHTMLDocument2 *pDoc = NULL;
IHTMLElement *pBody = NULL;
IHTMLElement2 *pBody2 = NULL;
IHTMLElementRender *pRender = NULL;
IDispatch *pDisp;
 
// ...............
// get the IWebBrowser2 interface from the ActiveX control
// ...............
 
if (wb) {
    // get the <body> element via IHTMLDocument2 interface
    if (SUCCEEDED(wb->get_Document(&pDisp)) && pDisp) {
        if (SUCCEEDED(pDisp->QueryInterface(IID_IHTMLDocument2, (void **) &pDoc)) && pDoc) {
            if (SUCCEEDED(pDoc->get_body(&pBody)) && pBody) {
 
                // get IHTMLElementRender for rendering, IHTMLElement2 for the the dimensions
                if (SUCCEEDED(pBody->QueryInterface(IID_IHTMLElementRender, (void **) &pRender)) && pRender
                        && SUCCEEDED(pBody->QueryInterface(IID_IHTMLElement2, (void **) &pBody2)) && pBody2) {
 
                    // get width & height
                    long width, height;
                    pBody2->get_clientWidth(&width);
                    pBody2->get_clientHeight(&height);
 
                    // create a bitmap with the same dimensions
                    Image *bitmap = new Bitmap(width, height);
 
                    // create a Graphics from Image
                    Graphics *g = Graphics::FromImage(bitmap);
 
                    HDC hDC = g->GetHDC();  // get the DC
                    pRender->DrawToDC(hDC); // draw to DC
                    g->ReleaseHDC(hDC);     // IMPORTANT: MUST RELEASE DC before calling any other GDI+ methods
 
                    CLSID bmpClsid;
                    GetEncoderClsid(L"image/bmp", &bmpClsid);  // helper function by MS
                    bitmap->Save(L"thumbnail.bmp", &bmpClsid); // save to "thumbnail.bmp"
 
                    pBody2->Release();
                    pRender->Release();
                }
 
                pBody->Release();
            }
 
            pDoc->Release();
        }
 
        pDisp->Release();
    }
 
    wb->Release();
}

Of course you need to initialize GDI+ by calling GdiplusStartup and call GdiplusShutdown when terminating.

A sample project can be downloaded from http://playground.softboysxp.org/IHTMLElementRenderDemo.zip

I used code from Michael Chourdakis in his codeproject article

Search MSDN Library for detailed documents on GDI+ and MSHTML.

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categories Programming | softboysxp, August 19, 2008 2:02 pm

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