 | So, how did I start this easy project? Opened the browser, Googled for it. What did I get as results? It's mid 2008 and I got (personal statistics here) : - 80% of samples, code snippet, suggestions using WebBrowser.DrawToBitmap
- 18% of IHTMLElementRender::DrawToDC
- 1% of Print screen
- 1% of IViewObject::Draw
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Obvioulsy, the WebBrowser is just a wrapper around IE. After all these years, solutions on Internet should be trustable? no?...nope.
The first solution, at first, seems very easy: navigate to your page (WebBrowser.Navigate), once you get the DocumentCompleted event, call DrawToBitmap. But that works only with simple web sites. For the others, we get what people on forums call: the white page.... empty image. So that means that it would mostly never work for today's web sites. (I've found one solution on the web that was generating the images correctly but it uses so much code to solve the problem (refresh and reload) and it was implemented in a WinForm).
The second solution, is a bit more complex but easy to implement. Same as the first solution, it all starts with a call to WebBrowser.Navigate and then wait for the DocumentCompleted event. There, I said to myself: "that is it!". I started to test my solution (keep in mind that at this point, I'm using a WinForm project for test purposes). It was all good until I arrived on finance.yahoo.com... Dooh, just some parts of the page were copied to my file... test, change code, test, modify here and there, test... nothing always the same %#^$% result. I needed something else.
The third worked but I was getting the browser frame included in the image... so abandoned this one quickly.
Finally, the last one, is the answer to the second solution's problem. What I've found, is that IHTMLElementRender does not deal with opacity (transparency). It doesn't draw it and that's why my image was missing some parts. I've found the solution from an old post from Nathan Moinvaziri. So, I implemented his easy solution that is to use IViewObject instead of IHTMLElementRender... and it worked with all the sites I was browsing to... wooohoo!
...but I'm not done yet. It now runs in a WinForm application and I don't want this WinForm to pop up on my server... obviously. So, I said to myself, I just have to create a simple class library, reference it from my web project and that's it!... hmmm, not exactly. STA... this is at least documented everywhere... the WebBrowser control needs to run within a Single-Threaded Apartment... long time I haven't heard about this term, hehehe.
Alright, I just have to do it this way... and it worked! Even for finance.yahoo.com! .... then I tried it with finance.yahoo.com/q?s=IBM ... #%^*!@ ... "Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))".... wtf is going on??? So, I'm getting exception on WebBrowser.ReadyState that I used in a "while" loop waiting for "WebBrowser.ReadyState == WebBrowserReadyState.Complete"... most of the code samples found for WebBrowser/STA do this trick... since I'm a dumass monkey, I did the same... alright, must be another way... I brought back my DocumentCompleted event but it's not obvious to deal with this since it has to be run within one call. I mixed the "while" loop with "Application.DoEvents()" to wait for the DocumentCompleted event be called and processed and then set a flag to "true" to exit the loop... here is the result:
public class ScreenCapturerSTA
{
private string m_url;
private byte[] m_byteImg;
private bool m_done = false;
private int m_tnWidth = 100;
private int m_tnHeight = 100;
/// <returns>Base64 string format</returns>
public string CaptureBase64(string url)
{
return Convert.ToBase64String(Capture(url));
}
public byte[] Capture(string url)
{
return Capture(url, 60000/*1 min*/);
}
public byte[] Capture(string url, int timeout)
{
m_url = url;
Thread t = new Thread(new ThreadStart(Capture));
t.Name = "screenCapturer";
t.SetApartmentState(ApartmentState.STA);
t.Start();
t.Join(timeout);
return m_byteImg;
}
private void Capture()
{
m_byteImg = null;
using (WebBrowser webBrowser = new WebBrowser())
{
webBrowser.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(webBrowser_DocumentCompleted);
webBrowser.Height = 1000;
webBrowser.Width = 1000;
webBrowser.ScriptErrorsSuppressed = true;
webBrowser.ScrollBarsEnabled = false;
webBrowser.Navigate(m_url);
while (!m_done)
{
Application.DoEvents();
}
}
}
void webBrowser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
if (e.Url == new Uri(m_url))//skip everything else
{
WebBrowser webBrowser = sender as WebBrowser;
try
{
int width = webBrowser.ClientRectangle.Width;
int height = webBrowser.ClientRectangle.Height;
IHTMLDocument2 doc2 = (IHTMLDocument2)webBrowser.Document.DomDocument;
using (Bitmap image = new Bitmap(width, height))
{
using (Graphics grfx = Graphics.FromImage(image))
{
grfx.Clear(Color.White);
_RECTL bounds;
bounds.left = 0;
bounds.top = 0;
bounds.right = width;
bounds.bottom = height;
IntPtr grfxHdc = grfx.GetHdc();
IViewObject viewObject = doc2 as IViewObject;
viewObject.Draw(1, -1, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero,
(IntPtr)grfxHdc, ref bounds, IntPtr.Zero, IntPtr.Zero, 0);
grfx.ReleaseHdc(grfxHdc);
}
using (Image thumbnailImage = image.GetThumbnailImage(m_tnWidth,
m_tnHeight, new Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero))
{
using (MemoryStream memstream = new MemoryStream())
{
thumbnailImage.Save(memstream, ImageFormat.Png);
m_byteImg = memstream.ToArray();
}
}
}
}
catch (Exception ex)
{
Debug.WriteLine(ex.ToString());
using (Bitmap image = new Bitmap(m_tnWidth, m_tnHeight))
{
using (Graphics grfx = Graphics.FromImage(image))
{
grfx.Clear(Color.White);
StringFormat format = new StringFormat();
format.LineAlignment = StringAlignment.Center;
format.Alignment = StringAlignment.Center;
using (SolidBrush brush = new SolidBrush(Color.FromArgb(61, 61, 61)))
{
grfx.DrawString("No image generated", new Font("arial", 6,
FontStyle.Bold, GraphicsUnit.Point), brush,
new Rectangle(0, 0, m_tnWidth, m_tnHeight), format);
}
}
using (MemoryStream memstream = new MemoryStream())
{
image.Save(memstream, ImageFormat.Png);
m_byteImg = memstream.ToArray();
}
}
}
finally
{
m_done = true;
}
}
}
public bool ThumbnailCallback()
{
return true;
}
}
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note: this hasn't been tested on a production environment yet, be careful!
Hopefully, it will serve fellow developers!
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