[Development] Rendering with different framerates into one scene

Jocelyn Turcotte jocelyn.turcotte at digia.com
Fri Mar 14 16:15:09 CET 2014

On Fri, Mar 14, 2014 at 04:12:02PM +0100, Jocelyn Turcotte wrote:
> On Fri, Mar 14, 2014 at 03:49:21PM +0100, Christoph Kurz wrote:
> > Now, if there is more than enough graphics power, ItemA and ItemB are rendered
> > with 60fps; If there is just enough power, ItemA is rendered with 40fps, ItemB
> > with 30fps. If there is not enough power for this, then ItemA could be rendered
> > with 20fps, ItemB with 15fps.
> If the scene is rendered without some items, those items will disapear
> from the screen as well, this is probably not what you waht. You could
> instead to store the result of the rendering of a complex branch of the
> scene into a FramebufferObject and simply blit it on frames where it isn't
> modified.
> This however comes at the price of using memory to store those pixels
> between frames.
> > Now the questions:
> > - Is that (or something similar) possible with the Qt scenegraph?
> "layer.enabled: true" should be enough to trigger intermediate rendering,
> but I haven't tried it myself so there might be some details I'm missing.
> http://qt-project.org/doc/qt-5/qml-qtquick-item.html#layer.enabled-prop
> > - How much effort would it be to implement it?
> Hopefully the above trick helps, the solution you propose sounds quite,
> humm, complex.
> > - Do you have useful links to additional articles / blogs that shed more light
> > on the scenegraph internals?
> For an overview: http://qt-project.org/doc/qt-5/qtquick-visualcanvas-scenegraph-renderer.html

Wrong link, this one is the actual overview:

> For more details the code is quite readable in most parts. Have a look
> under qtdeclarative/src/quick/scenegraph/.
> Cheers,
> Jocelyn
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