[Development] Do we have some plans about the damage tracking of QtQuick's scene graphics?

Giuseppe D'Angelo giuseppe.dangelo at kdab.com
Thu Jun 2 14:25:57 CEST 2022

On 02/06/2022 12:53, Shawn Rutledge wrote:
> In Qt Quick the strategy has been to build a complete scene graph for 
> all the contents of all visible items that you declared, and during 
> rending, the SG nodes that are not visible get culled; so we didn’t have 
> anything like QPaintEvent::region() to tell you what part of an Item is 
> “dirty”

I don't think that this is the problem here (i.e. partial updates within 
_one_ Item); rather, the fact that if any item in a scene needs to 
update, there's no damage-tracking mechanism to tell the underlying 
graphics layers that only a specific screen region has been damaged.

... or is there? QSG_VISUALIZE=changes does (used to do) exactly this. 
(I no longer remember if it shows an Item's bounding rectangle taking 
transformations into account, or an Item's actual geometry -- how does 
it do so in the presence of arbitrary vertex shaders?).

Properly signalling damage areas has a lot of interesting use cases, 
from compositors to efficiently enable remoting solutions (frame 

My 2 c,
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - The Qt, C++ and OpenGL Experts
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