Embedding 2D Drawing Objects in QWebView

One question not so easily answered is how to display high-frequently updated dynamic content in a QWebView. QWebView is a great tool to build hybrid web applications in C++. But because it is basically only a port of WebKit and Qt tries to wrap and encapsulate as much as possible, it is also only a plain web browser, just capable of displaying content that comes in HTML form. What if you want to display content within a web page like a stock chart or even a video…?

The options WebKit browsers offer are basically:

  • <object>, , <applet>: they each require you to implement a specific API and in case of applet even a different programming language
  • html 5.0 canvas: this is interesting, however, it requires JavaScript to program against it which might be to slow due to frequent parsing; it would be much more interesting if a QWebElement style wrapper would be available for drawing directly from C++
  • http://code.google.com/p/nativeclient/ is very interesting in normal browsers, but not in a hybrid application, as it is just another form of the <object> tag

This is why I have been thinking about a different approach, which is closer to the machine’s (i.e., Qt’s) drawing and came up with this idea:

Here we place a special, empty <div> in the document which can later be accessed by it’s ID using a QWebElement. We overwrite the QWebView::render() method and check if the region overlaps our dynamic content as specified by the QWebElement::geometry() data. The actual dynamic content can for instance be pre-rendered into an internal buffer, which we can use later as the source of a pixel copy operation towards the QWebKit paint device. Whenever our dynamic content changes, we can force a repaint via QWebView::repaint() exactly on the region that has changed.

Architecture-wise this just means that the main presentation layer of the hybrid app is not accessed in an outbound fashion only. I have no problem with that, as long as the dynamic content can be displayed and the module doing that can later be replaced with some less “hacked” approach…

03/05/2010 Update: HTML 5.0 Canvas is working in QWebView. I don’t know to what exact extent but some initial drawing tests completed successfully.

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