Re: [Interest] Qt3D/C++: How to disable rendering while makeing changes to the the Scenegraph
Am 20.06.22 um 10:08 schrieb Mike Krus: Hi On 20 Jun 2022, at 08:37, Yves Maurischat wrote: Hi all, I've got a C++/QWidgets application with 2 Qt3DWindow embedded. The 3D windows can be hidden (i.e. the user switches to another view), while work is done in other parts of the application. Whenever the user switches back to the view with the embedded Qt3DWindow there are a lot of changes to be made to the scenegraph. Rendering is set to OnDemand, but whenever the view is switched back to the 3D windows there is a big lag, up to several seconds. Profiling the application has shown that a lot of work is done for rendering at that point because the scenegraph is changing (most time is spent in the material classes). My working theory is, that each change to the scenegraph (i.e. removing entities, adding a new ones) causes a separate render update, which leads to the lag due to the amount of separate changes. that is not correct, updates are batched on a per-frame basis. If you’re not scheduling frames, no updates will be made. If you are using Qt version 5.15.0 or later this should be pretty fast. Prior version had a slower update mechanism. I'm on Qt 5.14.2 for the application, but this is a reason to switch to Qt 5.15.x One thing to keep in mind though is that changing materials will lead shaders needing to be recompiled, potentially textures to be updates, etc. Changing geometry means bounding volumes need updating, buffers need to be uploaded, etc. So the time might just be due to the GL state needing to be updated. You should take care to minimise such changes. I see. Currently large parts of the scenegraph are removed for an update but I guess I could optimize changes so only the absolute necessary parts are modified. Thanks! Another thing to note, if you have 2 Qt3DWindows, then you have 2 underlying Qt3DEngine instances. These do not share resources so everything might be done twice. Of course it’s impossible to provide accurate feedback without profiling the actual code. Mike So my question is: Is there a way to disable all render updates until the scenegraph has been updated/modified completely? What would be the "correct" way to make such changes? Is there something similar to the beginResetModel() and endResetModel() methods in QAbstractItemModel? Thanks! Yves ___ Interest mailing list Interest@qt-project.org https://lists.qt-project.org/listinfo/interest — Mike Krus | mike.k...@kdab.com | Senior Software Engineer & Teamlead KDAB (UK) Ltd., a KDAB Group company Tel: UK Office +44 1625 809908 Mobile +44 7833 491941 KDAB - The Qt Experts, C++, OpenGL Experts ___ Interest mailing list Interest@qt-project.org https://lists.qt-project.org/listinfo/interest
Re: [Interest] Qt3D/C++: How to disable rendering while makeing changes to the the Scenegraph
Hi > On 20 Jun 2022, at 08:37, Yves Maurischat > wrote: > > Hi all, > > I've got a C++/QWidgets application with 2 Qt3DWindow embedded. The 3D > windows can be hidden (i.e. the user switches to another view), while work is > done in other parts of the application. Whenever the user switches back to > the view with the embedded Qt3DWindow there are a lot of changes to be made > to the scenegraph. > > Rendering is set to OnDemand, but whenever the view is switched back to the > 3D windows there is a big lag, up to several seconds. Profiling the > application has shown that a lot of work is done for rendering at that point > because the scenegraph is changing (most time is spent in the material > classes). > > My working theory is, that each change to the scenegraph (i.e. removing > entities, adding a new ones) causes a separate render update, which leads to > the lag due to the amount of separate changes. that is not correct, updates are batched on a per-frame basis. If you’re not scheduling frames, no updates will be made. If you are using Qt version 5.15.0 or later this should be pretty fast. Prior version had a slower update mechanism. One thing to keep in mind though is that changing materials will lead shaders needing to be recompiled, potentially textures to be updates, etc. Changing geometry means bounding volumes need updating, buffers need to be uploaded, etc. So the time might just be due to the GL state needing to be updated. You should take care to minimise such changes. Another thing to note, if you have 2 Qt3DWindows, then you have 2 underlying Qt3DEngine instances. These do not share resources so everything might be done twice. Of course it’s impossible to provide accurate feedback without profiling the actual code. Mike > So my question is: Is there a way to disable all render updates until the > scenegraph has been updated/modified completely? What would be the "correct" > way to make such changes? Is there something similar to the > beginResetModel() and endResetModel() methods in QAbstractItemModel? > > > Thanks! > > Yves > > > > ___ > Interest mailing list > Interest@qt-project.org > https://lists.qt-project.org/listinfo/interest — Mike Krus | mike.k...@kdab.com | Senior Software Engineer & Teamlead KDAB (UK) Ltd., a KDAB Group company Tel: UK Office +44 1625 809908 Mobile +44 7833 491941 KDAB - The Qt Experts, C++, OpenGL Experts smime.p7s Description: S/MIME cryptographic signature ___ Interest mailing list Interest@qt-project.org https://lists.qt-project.org/listinfo/interest
[Interest] Qt3D/C++: How to disable rendering while makeing changes to the the Scenegraph
Hi all, I've got a C++/QWidgets application with 2 Qt3DWindow embedded. The 3D windows can be hidden (i.e. the user switches to another view), while work is done in other parts of the application. Whenever the user switches back to the view with the embedded Qt3DWindow there are a lot of changes to be made to the scenegraph. Rendering is set to /OnDemand/, but whenever the view is switched back to the 3D windows there is a big lag, up to several seconds. Profiling the application has shown that a lot of work is done for rendering at that point because the scenegraph is changing (most time is spent in the material classes). My working theory is, that each change to the scenegraph (i.e. removing entities, adding a new ones) causes a separate render update, which leads to the lag due to the amount of separate changes. So my question is: Is there a way to disable all render updates until the scenegraph has been updated/modified completely? What would be the "correct" way to make such changes? Is there something similar to the beginResetModel() and endResetModel() methods in QAbstractItemModel? Thanks! Yves ___ Interest mailing list Interest@qt-project.org https://lists.qt-project.org/listinfo/interest
