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Add support for painting at integer DPR with downscale

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Enable by setting QT_WIDGETS_HIGHDPI_DOWNSCALE=1 and QT_WIDGETS_RHI=1.

This will make the backing store and painter operate at the next
highest integer DPR in cases where QWindow::devicePixelRatio() returns
a fractional value. The backing store image will then be downscaled
to the target DPR at flush time, using the RHI flush pipeline.

[ChangeLog][QWidgets] Added experimental support for always
painting at an integer device pixel ratio (rounding the DPR up if
necessary), followed by a downscale to the target DPR.Enable by setting
QT_WIDGETS_HIGHDPI_DOWNSCALE=1 and QT_WIDGETS_RHI=1.

Pick-to: 6.4
Task-number: QTBUG-86344
Change-Id: Id5b834a0e3499818b0b656161f5e0c38a6caa340
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
This commit is contained in:
Morten Sørvig 2022-06-09 12:48:17 +02:00 committed by Morten Johan Sørvig
parent d38118c808
commit 79bead6c3b
4 changed files with 59 additions and 18 deletions
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48
src/gui/painting/qbackingstore.cpp
View File

@ -25,11 +25,32 @@ public:
{
}
// Returns the DPR for the backing store. This is the DPR for the QWindow,
// possibly rounded up to the nearest integer.
qreal backingStoreDevicePixelRatio() const
{
// Note: keep in sync with QWidget::metric()!
qreal windowDpr = window->devicePixelRatio();
return downscale ? std::ceil(windowDpr) : windowDpr;
}
// Returns the factor used for converting from device independent to native
// backing store sizes. Normally this is just the gui scale factor, however
// if the backing store rounds the DPR up to the nearest integer then we also
// need to account for the factor introduced by that rounding.
qreal deviceIndependentToNativeFactor() const
{
const qreal roundingFactor = backingStoreDevicePixelRatio() / window->devicePixelRatio();
const qreal guiFactor = QHighDpiScaling::factor(window);
return roundingFactor * guiFactor;
}
QWindow *window;
QPlatformBackingStore *platformBackingStore = nullptr;
QScopedPointer<QImage> highDpiBackingstore;
QRegion staticContents;
QSize size;
bool downscale = qEnvironmentVariableIntValue("QT_WIDGETS_HIGHDPI_DOWNSCALE") > 0;
};
/*!
@ -94,12 +115,14 @@ QWindow* QBackingStore::window() const
void QBackingStore::beginPaint(const QRegion &region)
{
const qreal dpr = d_ptr->backingStoreDevicePixelRatio();
if (d_ptr->highDpiBackingstore &&
d_ptr->highDpiBackingstore->devicePixelRatio() != d_ptr->window->devicePixelRatio())
d_ptr->highDpiBackingstore->devicePixelRatio() != dpr)
resize(size());
QPlatformBackingStore *platformBackingStore = handle();
platformBackingStore->beginPaint(QHighDpi::toNativeLocalRegion(region, d_ptr->window));
platformBackingStore->beginPaint(QHighDpi::scale(region, d_ptr->deviceIndependentToNativeFactor()));
// When QtGui is applying a high-dpi scale factor the backing store
// creates a "large" backing store image. This image needs to be
@ -118,8 +141,7 @@ void QBackingStore::beginPaint(const QRegion &region)
d_ptr->highDpiBackingstore.reset(
new QImage(source->bits(), source->width(), source->height(), source->bytesPerLine(), source->format()));
qreal targetDevicePixelRatio = d_ptr->window->devicePixelRatio();
d_ptr->highDpiBackingstore->setDevicePixelRatio(targetDevicePixelRatio);
d_ptr->highDpiBackingstore->setDevicePixelRatio(dpr);
}
}
}
@ -184,13 +206,15 @@ void QBackingStore::flush(const QRegion &region, QWindow *window, const QPoint &
Q_ASSERT(window == topLevelWindow || topLevelWindow->isAncestorOf(window, QWindow::ExcludeTransients));
QRegion nativeRegion = QHighDpi::toNativeLocalRegion(region, window);
const qreal toNativeFactor = d_ptr->deviceIndependentToNativeFactor();
QRegion nativeRegion = QHighDpi::scale(region, toNativeFactor);
QPoint nativeOffset;
if (!offset.isNull()) {
nativeOffset = QHighDpi::toNativeLocalPosition(offset, window);
nativeOffset = QHighDpi::scale(offset, toNativeFactor);
// Under fractional DPR, rounding of region and offset may accumulate to an off-by-one
QPoint topLeft = region.boundingRect().topLeft() + offset;
QPoint nativeTopLeft = QHighDpi::toNativeLocalPosition(topLeft, window);
QPoint nativeTopLeft = QHighDpi::scale(topLeft, toNativeFactor);
QPoint diff = nativeTopLeft - (nativeRegion.boundingRect().topLeft() + nativeOffset);
Q_ASSERT(qMax(qAbs(diff.x()), qAbs(diff.y())) <= 1);
nativeRegion.translate(diff);
@ -206,7 +230,7 @@ void QBackingStore::flush(const QRegion &region, QWindow *window, const QPoint &
void QBackingStore::resize(const QSize &size)
{
d_ptr->size = size;
handle()->resize(QHighDpi::toNativePixels(size, d_ptr->window), d_ptr->staticContents);
handle()->resize(QHighDpi::scale(size, d_ptr->deviceIndependentToNativeFactor()), d_ptr->staticContents);
}
/*!
@ -228,13 +252,13 @@ bool QBackingStore::scroll(const QRegion &area, int dx, int dy)
// Disable scrolling for non-integer scroll deltas. For this case
// the existing rendered pixels can't be re-used, and we return
// false to signal that a repaint is needed.
const qreal nativeDx = QHighDpi::toNativePixels(qreal(dx), d_ptr->window);
const qreal nativeDy = QHighDpi::toNativePixels(qreal(dy), d_ptr->window);
const qreal toNativeFactor = d_ptr->deviceIndependentToNativeFactor();
const qreal nativeDx = QHighDpi::scale(qreal(dx), toNativeFactor);
const qreal nativeDy = QHighDpi::scale(qreal(dy), toNativeFactor);
if (qFloor(nativeDx) != nativeDx || qFloor(nativeDy) != nativeDy)
return false;
return handle()->scroll(QHighDpi::toNativeLocalRegion(area, d_ptr->window),
nativeDx, nativeDy);
return handle()->scroll(QHighDpi::scale(area, toNativeFactor), nativeDx, nativeDy);
}
/*!

5
src/gui/painting/qbackingstoredefaultcompositor.cpp
View File

@ -408,7 +408,7 @@ void QBackingStoreDefaultCompositor::ensureResources(QRhiSwapChain *swapchain, Q
}
if (!m_sampler) {
m_sampler = m_rhi->newSampler(QRhiSampler::Nearest, QRhiSampler::Nearest, QRhiSampler::None,
m_sampler = m_rhi->newSampler(QRhiSampler::Linear, QRhiSampler::Linear, QRhiSampler::None,
QRhiSampler::ClampToEdge, QRhiSampler::ClampToEdge);
if (!m_sampler->create())
qWarning("QBackingStoreDefaultCompositor: Failed to create sampler");
@ -506,7 +506,8 @@ QPlatformBackingStore::FlushResult QBackingStoreDefaultCompositor::flush(QPlatfo
if (m_texture) {
// The backingstore is for the entire tlw.
// In case of native children offset tells the position relative to the tlw.
const QRect srcRect = toBottomLeftRect(deviceWindowRect.translated(deviceWindowOffset), m_texture->pixelSize().height());
const QRect textureRect = QRect(QPoint(), m_texture->pixelSize());
const QRect srcRect = toBottomLeftRect(textureRect.translated(deviceWindowOffset), m_texture->pixelSize().height());
const QMatrix3x3 source = sourceTransform(srcRect, m_texture->pixelSize(), origin);
QMatrix4x4 target; // identity
if (invertTargetY)

15
src/widgets/kernel/qwidget.cpp
View File

@ -12698,6 +12698,17 @@ int QWidget::metric(PaintDeviceMetric m) const
return QPaintDevice::metric(m);
}
auto resolveDevicePixelRatio = [this, screen]() -> qreal {
// Note: keep in sync with QBackingStorePrivate::backingStoreDevicePixelRatio()!
static bool downscale = qEnvironmentVariableIntValue("QT_WIDGETS_HIGHDPI_DOWNSCALE") > 0;
QWindow *window = this->window()->windowHandle();
if (downscale && window)
return std::ceil(window->devicePixelRatio());
return screen->devicePixelRatio();
};
switch (m) {
case PdmWidth:
return data->crect.width();
@ -12726,9 +12737,9 @@ int QWidget::metric(PaintDeviceMetric m) const
case PdmPhysicalDpiY:
return qRound(screen->physicalDotsPerInchY());
case PdmDevicePixelRatio:
return screen->devicePixelRatio();
return resolveDevicePixelRatio();
case PdmDevicePixelRatioScaled:
return QPaintDevice::devicePixelRatioFScale() * screen->devicePixelRatio();
return QPaintDevice::devicePixelRatioFScale() * resolveDevicePixelRatio();
default:
break;
}

9
tests/manual/highdpi/dprgadget/main.cpp
View File

@ -22,6 +22,7 @@ bool g_qtScaleFactor = false;
bool g_qtUsePhysicalDpi = false;
bool g_qtFontDpi = false;
bool g_qtScaleFactorRoundingPolicy = false;
bool g_qtHighDpiDownscale = false;
bool g_displayEvents = false;
@ -136,7 +137,7 @@ public:
if (g_displayEvents)
layout->addWidget(eventsLabel);
bool activeEnvironment = g_qtScaleFactor || g_qtUsePhysicalDpi || g_qtFontDpi || g_qtScaleFactorRoundingPolicy;
bool activeEnvironment = g_qtScaleFactor || g_qtUsePhysicalDpi || g_qtFontDpi || g_qtScaleFactorRoundingPolicy || g_qtHighDpiDownscale;
if (activeEnvironment) {
layout->addWidget(new QLabel("Active Environment:"));
if (g_qtScaleFactor) {
@ -155,7 +156,10 @@ public:
QString text = QString("QT_SCALE_FACTOR_ROUNDING_POLICY=") + qgetenv("QT_SCALE_FACTOR_ROUNDING_POLICY");
layout->addWidget(new QLabel(text));
}
if (g_qtHighDpiDownscale) {
QString text = QString("QT_WIDGETS_HIGHDPI_DOWNSCALE=") + qgetenv("QT_WIDGETS_HIGHDPI_DOWNSCALE");
layout->addWidget(new QLabel(text));
}
}
auto updateValues = [=]() {
@ -244,6 +248,7 @@ int main(int argc, char **argv) {
g_qtUsePhysicalDpi = qgetenv("QT_USE_PHYSICAL_DPI") == QByteArray("1");
g_qtFontDpi = qEnvironmentVariableIsSet("QT_FONT_DPI");
g_qtScaleFactorRoundingPolicy = qEnvironmentVariableIsSet("QT_SCALE_FACTOR_ROUNDING_POLICY");
g_qtHighDpiDownscale = qEnvironmentVariableIsSet("QT_WIDGETS_HIGHDPI_DOWNSCALE");
QApplication app(argc, argv);