Details
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Task
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Resolution: Unresolved
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P2: Important
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None
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6.4.0 Beta4
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None
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All
Description
Qt will always use the frame rate of your monitor to display content. For some reason, it updates 170 times a second on my 144hz monitor, resulting in an absurd amount of gpu usage. Note this video has 25fps, but it will get refreshed 170x/second on my monitor.
My quick and dirty fix for now is to call std::this_thread::sleep_for. Note FrameAnimation only works since 6.4:
limit to 60fps:
Sadly, I did not find another way to limit the fps.
QML:
FrameAnimation {
id:fi
running: true
property real fps: smoothFrameTime > 0 ? (1.0 / smoothFrameTime) : 0
onTriggered: {
fl.wait(smoothFrameTime)
}
}
Rectangle {
anchors.fill: fpsTxt
}
Text {
id:fpsTxt
text: fi.fps.toFixed(0)
font.pointSize: 24
anchors {
right:parent.right
margins: 20
}
}
header:
#pragma once #include <QObject> #include <QQmlEngine> class FrameLimiter : public QObject { Q_OBJECT QML_ELEMENT public: explicit FrameLimiter(QObject* parent = nullptr); Q_INVOKABLE void wait(float smoothFrameTime); private: const double maxFPS = 60.0; const double maxPeriod = 1.0 / maxFPS; };
cpp:
void FrameLimiter::wait(float smoothFrameTime) { float wait = maxPeriod * 2 - smoothFrameTime; int waitMs = wait * 1000; //qInfo() << "waitMs: " << waitMs << "= deltaTime" << smoothFrameTime << "- maxPeriod" << maxPeriod; std::this_thread::sleep_for(std::chrono::milliseconds(waitMs)); }
I think this is a broader issue with Qt (also happens for example with custom shader that always run at maximum refresh rate), because it does not always make sense to render at full speed. Every modern game for example has the option to limit the fps if the window is no longer in focus to save power. lagocs this should be your area of expertise, right?
