Differential D11938 Diff 29768 files/0002-Fix-perf-regression-when-avoiding-scrollbar-flipping.patch

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files/0002-Fix-perf-regression-when-avoiding-scrollbar-flipping.patch

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				From ffc9323671d045e3566980d9ed4567f071004e65 Mon Sep 17 00:00:00 2001
				From: Volker Hilsheimer <volker.hilsheimer@qt.io>
				Date: Thu, 28 Oct 2021 16:55:33 +0200
				Subject: Fix performance regression when avoiding scrollbar flipping

				Amends 6c4dc722cb9bf765904feefff4fb00bdb0b3dc9f.

				Don't search for the optimal size of the scrollarea's widget if it can't
				be found anyway. Try the size with scrollbar first, which covers the
				vast majority of sizes.

				Optimizing the loop with e.g. a binary search adds no value, as the size
				is often just a pixel too small.

				Since we can't rely on the number of height-for-width calls, we can't
				meaningfully test this behavior. The number of calls is still very high
				during showing and resizing; optimizing this further is for a separate
				commit.

				Fixes: QTBUG-97811
				Pick-to: 6.2 5.15
				Change-Id: If145302e6414b32cf1ce7251ff33b0039f584867
				Reviewed-by: Jonas Kvinge <jonas@jkvinge.net>
				Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
				---
				src/widgets/widgets/qscrollarea.cpp \| 11 +++++++----
				1 file changed, 7 insertions(+), 4 deletions(-)

				diff --git a/src/widgets/widgets/qscrollarea.cpp b/src/widgets/widgets/qscrollarea.cpp
				index f880240ea7..e8fdadb648 100644
				--- a/src/widgets/widgets/qscrollarea.cpp
				+++ b/src/widgets/widgets/qscrollarea.cpp
				@@ -203,10 +203,13 @@ void QScrollAreaPrivate::updateScrollBars()
				if (vbarpolicy == Qt::ScrollBarAsNeeded) {
				int vbarWidth = vbar->sizeHint().width();
				QSize m_hfw = m.expandedTo(min).boundedTo(max);
				- while (h > m.height() && vbarWidth) {
				- --vbarWidth;
				- --m_hfw.rwidth();
				- h = widget->heightForWidth(m_hfw.width());
				+ // is there any point in searching?
				+ if (widget->heightForWidth(m_hfw.width() - vbarWidth) <= m.height()) {
				+ while (h > m.height() && vbarWidth) {
				+ --vbarWidth;
				+ --m_hfw.rwidth();
				+ h = widget->heightForWidth(m_hfw.width());
				+ }
				}
				max = QSize(m_hfw.width(), qMax(m_hfw.height(), h));
				}
				--
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