54 lines
2.2 KiB
Diff
54 lines
2.2 KiB
Diff
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From ffc9323671d045e3566980d9ed4567f071004e65 Mon Sep 17 00:00:00 2001
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From: Volker Hilsheimer <volker.hilsheimer@qt.io>
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Date: Thu, 28 Oct 2021 16:55:33 +0200
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Subject: Fix performance regression when avoiding scrollbar flipping
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Amends 6c4dc722cb9bf765904feefff4fb00bdb0b3dc9f.
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Don't search for the optimal size of the scrollarea's widget if it can't
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be found anyway. Try the size with scrollbar first, which covers the
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vast majority of sizes.
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Optimizing the loop with e.g. a binary search adds no value, as the size
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is often just a pixel too small.
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Since we can't rely on the number of height-for-width calls, we can't
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meaningfully test this behavior. The number of calls is still very high
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during showing and resizing; optimizing this further is for a separate
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commit.
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Fixes: QTBUG-97811
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Pick-to: 6.2 5.15
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Change-Id: If145302e6414b32cf1ce7251ff33b0039f584867
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Reviewed-by: Jonas Kvinge <jonas@jkvinge.net>
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Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
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---
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src/widgets/widgets/qscrollarea.cpp | 11 +++++++----
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1 file changed, 7 insertions(+), 4 deletions(-)
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diff --git a/src/widgets/widgets/qscrollarea.cpp b/src/widgets/widgets/qscrollarea.cpp
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index f880240ea7..e8fdadb648 100644
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--- a/src/widgets/widgets/qscrollarea.cpp
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+++ b/src/widgets/widgets/qscrollarea.cpp
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@@ -203,10 +203,13 @@ void QScrollAreaPrivate::updateScrollBars()
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if (vbarpolicy == Qt::ScrollBarAsNeeded) {
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int vbarWidth = vbar->sizeHint().width();
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QSize m_hfw = m.expandedTo(min).boundedTo(max);
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- while (h > m.height() && vbarWidth) {
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- --vbarWidth;
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- --m_hfw.rwidth();
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- h = widget->heightForWidth(m_hfw.width());
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+ // is there any point in searching?
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+ if (widget->heightForWidth(m_hfw.width() - vbarWidth) <= m.height()) {
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+ while (h > m.height() && vbarWidth) {
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+ --vbarWidth;
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+ --m_hfw.rwidth();
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+ h = widget->heightForWidth(m_hfw.width());
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+ }
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}
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max = QSize(m_hfw.width(), qMax(m_hfw.height(), h));
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}
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--
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cgit v1.2.1
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