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offscreen: Enable backingstore images with alpha

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Grabbing a QQuickWindow (software backend) cleared to something
semi-transparent is not going to be correct otherwise.

Pick-to: 6.9 6.8
Task-number: QTBUG-136755
Change-Id: I59f378b177154af25b1d7bff878435c715e3d114
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
This commit is contained in:
Laszlo Agocs 2025-05-13 14:38:13 +02:00
parent 44b5602536
commit 97f7819f1d
2 changed files with 15 additions and 1 deletions
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15
src/plugins/platforms/offscreen/qoffscreencommon.cpp
View File

@ -148,7 +148,9 @@ void QOffscreenBackingStore::flush(QWindow *window, const QRegion &region, const
void QOffscreenBackingStore::resize(const QSize &size, const QRegion &)
{
QImage::Format format = QGuiApplication::primaryScreen()->handle()->format();
QImage::Format format = window()->format().hasAlpha()
? QImage::Format_ARGB32_Premultiplied
: QGuiApplication::primaryScreen()->handle()->format();
if (m_image.size() != size)
m_image = QImage(size, format);
clearHash();
@ -167,6 +169,17 @@ bool QOffscreenBackingStore::scroll(const QRegion &area, int dx, int dy)
return true;
}
void QOffscreenBackingStore::beginPaint(const QRegion &region)
{
if (QImage::toPixelFormat(m_image.format()).alphaUsage() == QPixelFormat::UsesAlpha) {
QPainter p(&m_image);
p.setCompositionMode(QPainter::CompositionMode_Source);
const QColor blank = Qt::transparent;
for (const QRect &r : region)
p.fillRect(r, blank);
}
}
QPixmap QOffscreenBackingStore::grabWindow(WId window, const QRect &rect) const
{
QRect area = m_windowAreaHash.value(window, QRect());

1
src/plugins/platforms/offscreen/qoffscreencommon.h
View File

@ -68,6 +68,7 @@ public:
void flush(QWindow *window, const QRegion &region, const QPoint &offset) override;
void resize(const QSize &size, const QRegion &staticContents) override;
bool scroll(const QRegion &area, int dx, int dy) override;
void beginPaint(const QRegion &) override;
QPixmap grabWindow(WId window, const QRect &rect) const;
QImage toImage() const override { return m_image; }