If the transform matrix is an identity, then positioning wont change and
we can avoid creating the transform node altogether. This is based on
a similar find in GTK today while reducing temporary allocations.
This cuts the number of transforms created in clutter_actor_paint() by
about half under light testing of GNOME Shell from 6.8% to 2.4% of
allocations.
Before:
ALLOCATED TOTAL FUNCTION
[ 20.4 MiB] [ 21.20%] clutter_actor_paint
[ 11.0 MiB] [ 11.45%] clutter_paint_node_paint
[ 6.6 MiB] [ 6.84%] clutter_transform_node_new
[ 2.5 MiB] [ 2.61%] clutter_actor_node_new
After:
ALLOCATED TOTAL FUNCTION
[ 33.4 MiB] [ 24.12%] clutter_actor_paint
[ 26.2 MiB] [ 18.91%] clutter_paint_node_paint
[ 3.4 MiB] [ 2.43%] clutter_actor_node_new
[ 3.3 MiB] [ 2.41%] clutter_transform_node_new
Allocation amounts will have differed due to different amounts of running
time, but the % of allocations has now dropped below
clutter_actor_node_new() which should be expected.
https://gitlab.gnome.org/GNOME/mutter/issues/1056
d122b66abc