[Development] Rendering only items that are visible in Qt Quick

[Albert Astals Cid]

El divendres, 23 de març de 2018, a les 14:44:03 CET, Mitch Curtis va 
escriure:
> I'd like to get some discussion going around this:
> 
> https://bugreports.qt.io/browse/QTBUG-67274
> 
> As I understand it, clipping (the "clip" property) doesn't prevent items
> that aren't visible (in the sense of being out of the viewport, not the
> "visible" property) from actually being rendered.
> 
> It would be useful if we had a way to do this with minimal effort from the
> user. I'm thinking of a e.g. a property or flag in QQuickItem that, when
> set, would cause the scenegraph to use the shape (could start off as just
> being a bounding rect) of child items to determine whether or not that item
> is visible with regards to its parents bounding rect. That way, any regular
> old item can benefit from it easily.
> 
> Does anyone else have ideas about this?

The culled property of QQuickItemPrivate makes things be skipped for 
rendering, so you could add something like 
QQuickItemPrivate::setChildrenCulled that used the geometries of children to 
set it's culled property.

The problem is that this can get relatively inefficient if those geometries 
change (animations, etc) since you have to recalculate the culled property for 
every single change so given how supposedly fast graphics are at clipping you 
may be better of just using clipping?

Cheers,
  Albert

> 
> Comments about how it will never work and I should feel bad for suggesting
> it?
> 
> Far superior alternatives?
> 
> Please, share your thoughts! :D
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Albert Astals Cid | albert.astals.cid at kdab.com | Software Engineer
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