Performance issues when disabling client side decorations with "GTK_CSD=0"

Submitted by Eduard Braun

Assigned to gtk-win32 maintainers

Description

Created attachment 349623 Modified version of "fishbowl.ui" that allows disabling CSD

When disabling client side decorations via the environment variable "GTK_CSD=0" drawing performance seems significantly reduced.

This issue was initially discovered in MSYS2 builds of Inkscape trunk (see [1]) where disabling client side decorations causes severe performance regressions when moving objects but also has an overall negative impact on UI performance.

The issue can also be reproduced and quantified with the "Fishbowl" benchmark in "gtk3-demo" (one has to use a modified version of "fishbowl.ui" that does remove the titlebar customizations, otherwise CSDs will be forced, see attachment):

with "GTK_CSD=1": ~950 icons at ~55 fps
with "GTK_CSD=1": ~150 icons at ~55 fps

[1] http://inkscape.13.x6.nabble.com/slow-dragging-on-Windows-tp4979387.html

Attachment 349623, "Modified version of "fishbowl.ui" that allows disabling CSD":
fishbowl.ui

Version: 3.22.x