From bdf9dec41193b2cdfb27c0b067b883b58b2fd8f1 Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Tue, 24 Jun 2025 19:17:47 -0600
Subject: [PATCH] pianoroll: if invisible, defer (expensive) ::set_region()
 till shown

---
 gtk2_ardour/pianoroll.cc | 16 +++++++++++++++-
 gtk2_ardour/pianoroll.h  |  3 +++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/gtk2_ardour/pianoroll.cc b/gtk2_ardour/pianoroll.cc
index 02dfe7dbe5..6d6a62c092 100644
--- a/gtk2_ardour/pianoroll.cc
+++ b/gtk2_ardour/pianoroll.cc
@@ -639,10 +639,19 @@ Pianoroll::build_canvas ()
 	_canvas->set_name ("MidiCueCanvas");
 	_canvas->add_events (Gdk::POINTER_MOTION_HINT_MASK | Gdk::SCROLL_MASK | Gdk::KEY_PRESS_MASK | Gdk::KEY_RELEASE_MASK);
 	_canvas->set_can_focus ();
-
+	_canvas->signal_show().connect (sigc::mem_fun (*this, &Pianoroll::catch_pending_show_region));
 	_toolbox.pack_start (*_canvas_viewport, true, true);
 }
 
+void
+Pianoroll::catch_pending_show_region ()
+{
+	if (_visible_pending_region) {
+		set_region (_visible_pending_region);
+		_visible_pending_region.reset ();
+	}
+}
+
 bool
 Pianoroll::bbt_ruler_event (GdkEvent* ev)
 {
@@ -2603,6 +2612,11 @@ Pianoroll::update_solo_display ()
 void
 Pianoroll::set_region (std::shared_ptr<ARDOUR::MidiRegion> r)
 {
+	if (!get_canvas()->is_visible()) {
+		_visible_pending_region = r;
+		return;
+	}
+
 	unset (false);
 
 	if (!r) {
diff --git a/gtk2_ardour/pianoroll.h b/gtk2_ardour/pianoroll.h
index bfde56746e..da821fd75d 100644
--- a/gtk2_ardour/pianoroll.h
+++ b/gtk2_ardour/pianoroll.h
@@ -352,4 +352,7 @@ class Pianoroll : public CueEditor
 
 	Gtk::Menu _region_context_menu;
 	void popup_region_context_menu (ArdourCanvas::Item* item, GdkEvent* event);
+
+	std::shared_ptr<ARDOUR::MidiRegion> _visible_pending_region;
+	void catch_pending_show_region ();
 };