[Qt-interest] Paint QWebView to a QImage

[Richard Hosking]

Many thanks for the advice.  The repaintRequested approach seems to
be the ideal method for me.

I have implemented this, but I am getting Painter errors:-

"A paint device can only be painted by one painter at a time"

...when painting to the QImage upon each repaintRequested call.
I suspect some concurrency issues here on my part!

I have attached my very stripped down test code which highlights
my issue.  What do I need to do to make this work?  Do I need to
'queue' the paint events myself so they do not overlap?

Richard.

(Qt 4.5.1 on Ubuntu 9.04)

Girish Ramakrishnan wrote:
> Hi,
> Use a plain QWebPage and connect to it' repaintRequested(QRect). You can
> then pass that QRect to QWebFrame's render() to update only the portion
> that got changed.
> 
> (Also, your approach on changing the paintEngine won't work. Just
> reimplementing QWidget::paintEngine() doesn't actually switch the paint
> engine - It's complicated)
> 
> Girish
> 
> Richard Hosking wrote:
>> Hello, I am trying to render the contents of a QWebView
>> to a QImage instance.
>>
>> I have tried the QWebFrame->render(QImage) method, but this
>> is not the correct approach for me as I need to render
>> at several frames a second.  I really only want to render
>> when changes occur on the widget to keep CPU usage down.
>>
>> What I would ideally like is for QWebView to render directly
>> to a QImage.
>>
>> I have tried subclassing QWebView's paintEngine() and
>> returning my QImage->paintEngine() but the image remains
>> unchanged.
>>
>> I have also tried hooking into QWebView's event() and
>> listening for QEvent::Paint then calling
>> QPainter::setRedirected(QWebView, QImage) but again nothing
>> is produced in the image.
>>
>> Any pointers?
>>
>> (Qt 4.5.1 on Linux)
>>
>> Kind regards,
>> Richard.
> 
> 
> 
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