[qt/qt/qtquick3d]: Summary of bulk changes made

Git repository change summary for qt/qt/qtquick3d
Pushed by mirror-service into branch '6.12'.
Changed from 0244eb04cf339bba4fda33c959187f484f315a78 to 4642d6ac6713f4ae71dfd4f8a28121ced8b6bb57
Acknowledgement was received that this change introduces only existing code that has been pushed to another public open source repository.

This change contains the following new commits:

Git commit 0c44de171871cb5c26944eecdad5664868b3d498 by Qt Cherry-pick Bot (on behalf of Christian Strømme) on 05/08/2026 at 10:42..
Fix layers support for particles

The particle system creates hidden internal nodes that do not take
part in the normal processing, meaning the particle system needs to
maintain and update the layers for the nodes it creates itself. This
was unfortunately missed in the initial implementation.
Note that this only applies to the internally created nodes, like the
sprite and line particles. For content  the instantiated from a
user-provided delegate (ModelParticle3D and ModelBlendParticle3D) the
layers property is left alone, since the layers property is not inherited
and stamping user content would override explicit layer assignments
made in the delegate. While this design causes a slightly different
behavior for the two types of particles, it follows intended behavior
of the layers API and also avoids that we try to be cleaver and guess
what the user actually wants to do.

Added particle effects to the layers example, including a model
particle with a compound delegate where each model assigns its own
content layer, and a visual test.

Pick-to: 6.11 6.11.2
Change-Id: I0b2b08dfe6e19b7cbf4fcde81e485f1c360ef99b
Reviewed-by: Tomi Korpipää <[email protected]>
(cherry picked from commit d8f207d32a2c87b15be15548129eb25c5b205002)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>
https://invent.kde.org/qt/qt/qtquick3d/-/commit/0c44de171871cb5c26944eecdad5664868b3d498

Git commit 4642d6ac6713f4ae71dfd4f8a28121ced8b6bb57 by Qt Cherry-pick Bot (on behalf of Christian Strømme) on 05/08/2026 at 15:10..
Add some heuristics for when to parallelize the model data calculations

The cost of parallelizing and synchronization will be higher then the
cost of just doing the calculations of the normal matrix and MVP
sequentially on the calling thread. Even on modern and powerful machines
this becomes visible while benchmarking. The right cut-off value can be
hard to determine as it will depend on the target hardware, so the exact
value is configurable through an environment variable. By default we cut
off at 32, which should filter out the smallest scene from paying the
overhead. In addition the synchronization primitives are guarded and
made into member variables; This ensures the cost of using them aren't
paid when for small scenes and that we don't re-creating them each
frame.

Pick-to: 6.11
Change-Id: I7813e52ad224ad770c6dde7699fe46caa1ded024
Reviewed-by: Andy Nichols <[email protected]>
(cherry picked from commit 48ae00cd622f350be2cac2e9fd1b279e42829516)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>
https://invent.kde.org/qt/qt/qtquick3d/-/commit/4642d6ac6713f4ae71dfd4f8a28121ced8b6bb57