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High-DPI: Set the minimum scale factor to 1

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Avoid painting errors with dpr < 1, also for the PassThrough
mode.

This limits the minimum high-dpi scale factor to 1,
for the code path which determines the scale factor
based on screen DPI.

Task-number: QTBUG-89948
Change-Id: I14b3f130f0ae141d5f05c87437f926a9f76d1dec
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit ee409e6f0cab4aa051f75f7c7116d4b607d137fc)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Morten Johan Sørvig 2021-02-24 00:06:26 +01:00 committed by Qt Cherry-pick Bot
parent 93f46f303e
commit 667d0eb3c5
2 changed files with 18 additions and 5 deletions
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8
src/gui/kernel/qhighdpiscaling.cpp
View File

@ -436,11 +436,9 @@ qreal QHighDpiScaling::roundScaleFactor(qreal rawFactor)
break;
}
// Don't round down to to zero; clamp the minimum (rounded) factor to 1.
// This is not a common case but can happen if a display reports a very
// low DPI.
if (scaleFactorRoundingPolicy != Qt::HighDpiScaleFactorRoundingPolicy::PassThrough)
roundedFactor = qMax(roundedFactor, qreal(1));
// Clamp the minimum factor to 1. Qt does not currently render
// correctly with factors less than 1.
roundedFactor = qMax(roundedFactor, qreal(1));
return roundedFactor;
}

15
tests/auto/gui/kernel/qhighdpi/tst_qhighdpi.cpp
View File

@ -49,6 +49,7 @@ private slots:
void initTestCase();
void qhighdpiscaling_data();
void qhighdpiscaling();
void minimumDpr();
void noscreens();
void screenDpiAndDpr_data();
void screenDpiAndDpr();
@ -223,6 +224,20 @@ void tst_QHighDpi::screenDpiAndDpr()
}
}
void tst_QHighDpi::minimumDpr()
{
QList<qreal> dpiValues { 40, 60, 95 };
std::unique_ptr<QGuiApplication> app(createStandardOffscreenApp(dpiValues));
for (QScreen *screen : app->screens()) {
// Qt does not currently support DPR values < 1. Make sure
// the minimum DPR value is 1, also when the screen reports
// a low DPI.
QCOMPARE(screen->devicePixelRatio(), 1);
QWindow window(screen);
QCOMPARE(window.devicePixelRatio(), 1);
}
}
void tst_QHighDpi::noscreens()
{
// Create application object with a no-screens configuration (should not crash)