From 68032fc59ae4c8a2cb372e5781a440d7cdaefa6e Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 12 Apr 2025 07:38:33 +0530
Subject: [PATCH] Cache heightForWIdth calculation as recommended by Qt docs

---
 src/calibre/gui2/widgets2.py | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/calibre/gui2/widgets2.py b/src/calibre/gui2/widgets2.py
index b2f2e881bd..5457a13a69 100644
--- a/src/calibre/gui2/widgets2.py
+++ b/src/calibre/gui2/widgets2.py
@@ -408,10 +408,22 @@ class FlowLayout(QLayout):  # {{{
     def __init__(self, parent=None):
         QLayout.__init__(self, parent)
         self.items = []
+        self.height_for_width_cache = {}
+
+    def clear_caches(self):
+        self.height_for_width_cache.clear()
 
     def addItem(self, item):
+        self.clear_caches()
         self.items.append(item)
 
+    def isEmpty(self):
+        return not bool(self.items)
+
+    def invalidate(self):
+        self.clear_caches()
+        super().invalidate()
+
     def itemAt(self, idx):
         try:
             return self.items[idx]
@@ -432,7 +444,9 @@ class FlowLayout(QLayout):  # {{{
         return True
 
     def heightForWidth(self, width):
-        return self.do_layout(QRect(0, 0, width, 0), apply_geometry=False)
+        if (ans := self.height_for_width_cache.get(width)) is None:
+            ans = self.height_for_width_cache[width] = self.do_layout(QRect(0, 0, width, 0), apply_geometry=False)
+        return ans
 
     def setGeometry(self, rect):
         QLayout.setGeometry(self, rect)