From d3c673e20b3a0b189ea75bb0e03b44b4de3c6757 Mon Sep 17 00:00:00 2001
From: Peter Nelson <peter1138@openttd.org>
Date: Sat, 27 Jan 2024 18:44:27 +0000
Subject: [PATCH] Fix #11894: Defer window OnResize event to avoid processing
 multiple times per input tick. (#11900)

---
 src/window.cpp   | 29 +++++++++++++++++++++++++----
 src/window_gui.h |  3 +++
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/window.cpp b/src/window.cpp
index 3287159da1..a33c3c0177 100644
--- a/src/window.cpp
+++ b/src/window.cpp
@@ -1447,8 +1447,8 @@ void Window::FindWindowPlacementAndResize(int def_width, int def_height)
 		ResizeWindow(this, enlarge_x, enlarge_y);
 		/* ResizeWindow() calls this->OnResize(). */
 	} else {
-		/* Always call OnResize; that way the scrollbars and matrices get initialized. */
-		this->OnResize();
+		/* Schedule OnResize; that way the scrollbars and matrices get initialized. */
+		this->ScheduleResize();
 	}
 
 	int nx = this->left;
@@ -2050,8 +2050,8 @@ void ResizeWindow(Window *w, int delta_x, int delta_y, bool clamp_to_screen)
 
 	EnsureVisibleCaption(w, w->left, w->top);
 
-	/* Always call OnResize to make sure everything is initialised correctly if it needs to be. */
-	w->OnResize();
+	/* Schedule OnResize to make sure everything is initialised correctly if it needs to be. */
+	w->ScheduleResize();
 	w->SetDirty();
 }
 
@@ -3054,6 +3054,7 @@ void UpdateWindows()
 
 	/* Process invalidations before anything else. */
 	for (Window *w : Window::Iterate()) {
+		w->ProcessScheduledResize();
 		w->ProcessScheduledInvalidations();
 		w->ProcessHighlightedInvalidations();
 	}
@@ -3111,6 +3112,26 @@ void SetWindowClassesDirty(WindowClass cls)
 	}
 }
 
+/**
+ * Mark this window as resized and in need of OnResize() event.
+ */
+void Window::ScheduleResize()
+{
+	this->scheduled_resize = true;
+}
+
+/**
+ * Process scheduled OnResize() event.
+ */
+void Window::ProcessScheduledResize()
+{
+	/* Sometimes OnResize() resizes the window again, in which case we can reprocess immediately. */
+	while (this->scheduled_resize) {
+		this->scheduled_resize = false;
+		this->OnResize();
+	}
+}
+
 /**
  * Mark this window's data as invalid (in need of re-computing)
  * @param data The data to invalidate with
diff --git a/src/window_gui.h b/src/window_gui.h
index a6a94496e2..d4171070cf 100644
--- a/src/window_gui.h
+++ b/src/window_gui.h
@@ -274,6 +274,7 @@ protected:
 	virtual void FindWindowPlacementAndResize(int def_width, int def_height);
 
 	std::vector<int> scheduled_invalidation_data;  ///< Data of scheduled OnInvalidateData() calls.
+	bool scheduled_resize; ///< Set if window has been resized.
 
 	/* Protected to prevent deletion anywhere outside Window::DeleteClosedWindows(). */
 	virtual ~Window();
@@ -559,6 +560,8 @@ public:
 
 	void SetShaded(bool make_shaded);
 
+	void ScheduleResize();
+	void ProcessScheduledResize();
 	void InvalidateData(int data = 0, bool gui_scope = true);
 	void ProcessScheduledInvalidations();
 	void ProcessHighlightedInvalidations();