[Qt-interest] Fast Scaling of Images

[Joshua Grauman]

This is definitely helpful and good ideas. Can hardware acceleration help 
here? I've never used openGL, would it be possible to pass off scaling of 
the image to openGL? If so, can anyone get me started in the right 
direction for how to do that?

Josh

> Check your render hints, back them down until you're done scaling to the final
> resolution.
>
>
> There is also a fast scale algorithm on labs.qt.nokia.com but only works for 1/2
> sizes. In fact there are several optimization articles there.
>
>
>
> ----- Original Message ----
> From: Joshua Grauman <jnfo-c at grauman.com>
> To: qt-interest at qt.nokia.com
> Sent: Fri, April 15, 2011 1:32:11 PM
> Subject: [Qt-interest] Fast Scaling of Images
>
> Hello all,
>
> I'd like to include a simple image viewer in my application to view
> several pngs (around 2000 x 3000 resolution), viewed roughly full screen
> (ie. 1000 x 700 or so). I'd like to user to be able to zoom in/out and
> pan/scroll. I've seen some examples that simply use a QScrollArea with a
> QLabel to display the image. This works fine for me, but I was wondering
> if there might be a better method that would scale the images faster so
> that zoom in/out would be smoother. The examples I've seen simply use
> QLabel::resize() to do the scaling. Is this about as good as I'll get, or
> would there be a noticably faster method (reimplementing QPaintEvent??)?
> Obviously, I could cache several zoom sizes when each image is loaded, I'm
> still thinking if that would be worth it. For now I'm just seeing if there
> is a significantly faster method for doing the actual zooming than via
> QLabel::resize(). Thoughts? Thanks!
>
> Josh
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