[viruslobster]

Until gtk 4.20.1 trackpads have kinetic scrolling behavior regardless of Gtk.ScrolledWindow.kinetic_scrolling. As a workaround, set EventControllerScroll.kinetic to false on all controllers.

observeControllers() has this warning:

Calling this function will enable extra internal bookkeeping to track controllers and emit signals on the returned listmodel. It may slow down operations a lot.
Applications should try hard to avoid calling this function because of the slowdowns.

but judging from the source this is a one time penalty since we free the result immediately afterwards.

Fixes #11460.

AI usage

Zed + Opus 4.5 generated the first pass, but it missed freeing the result of observeControllers() and conveniently binding scrolled_window to the blueprint. Figuring out what was going on also took a lot of human debugging.

[jcollie]

I can't really test because I don't have access to a trackpad on a system running an affected version of GTK, so mostly going to have to trust that this doesn't break things for some people. A couple of changes requested though.

[jcollie]

You don't have to cast the controller back to a GObject to unref it.
A while loop to iterate over the controllers works better I think.
The objects returned by getObject need to be unref'd.

diff --git a/src/apprt/gtk/class/surface_scrolled_window.zig b/src/apprt/gtk/class/surface_scrolled_window.zig
index 8edada988..dd4f17d11 100644
--- a/src/apprt/gtk/class/surface_scrolled_window.zig
+++ b/src/apprt/gtk/class/surface_scrolled_window.zig
@@ -74,9 +74,10 @@ pub const SurfaceScrolledWindow = extern struct {
         // of `Gtk.ScrolledWindow.kinetic_scrolling`. As a workaround, disable
         // EventControllerScroll.kinetic
         const controllers = self.private().scrolled_window.as(gtk.Widget).observeControllers();
-        defer controllers.as(gobject.Object).unref();
-        for (0..controllers.getNItems()) |i| {
-            const obj = controllers.getObject(@intCast(i)) orelse continue;
+        defer controllers.unref();
+        var i: c_uint = 0;
+        while (controllers.getObject(i)) |obj| : (i += 1) {
+            defer obj.unref();
             const controller = gobject.ext.cast(gtk.EventControllerScroll, obj) orelse continue;
             var flags = controller.getFlags();
             flags.kinetic = false;

[viruslobster]

@jcollie Thanks for the review and good catch with freeing the obj. I assumed that would be a shared reference but the docs do say otherwise.

I just pushed the update.

[jcollie]

LGTM pending CI