macOS: Implement QCALayerBackingStore::toImage()

It's not part of the QBackingStore API, but clients such as the Qt Quick
software renderer access it through the platform backingstore, to grab
the window.

Change-Id: I203484ce13a5f8fb6815d27ab07f874fa9d16b8c
Fixes: QTBUG-75467
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

2 files changed, 16 insertions, 0 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoabackingstore.h b/src/plugins/platforms/cocoa/qcocoabackingstore.h
index 470da63e3d..acddc3ecc8 100644
--- a/src/plugins/platforms/cocoa/qcocoabackingstore.h
+++ b/src/plugins/platforms/cocoa/qcocoabackingstore.h
@@ -81,6 +81,7 @@ public:
         QPlatformTextureList *textures, bool translucentBackground) override;
 #endif
 
+    QImage toImage() const override;
     QPlatformGraphicsBuffer *graphicsBuffer() const override;
 
 private:
diff --git a/src/plugins/platforms/cocoa/qcocoabackingstore.mm b/src/plugins/platforms/cocoa/qcocoabackingstore.mm
index e786ecb5a5..cff1f96615 100644
--- a/src/plugins/platforms/cocoa/qcocoabackingstore.mm
+++ b/src/plugins/platforms/cocoa/qcocoabackingstore.mm
@@ -534,6 +534,21 @@ void QCALayerBackingStore::composeAndFlush(QWindow *window, const QRegion &regio
 }
 #endif
 
+QImage QCALayerBackingStore::toImage() const
+{
+    if (!const_cast<QCALayerBackingStore*>(this)->prepareForFlush())
+        return QImage();
+
+    // We need to make a copy here, as the returned image could be used just
+    // for reading, in which case it won't detach, and then the underlying
+    // image data might change under the feet of the client when we re-use
+    // the buffer at a later point.
+    m_buffers.back()->lock(QPlatformGraphicsBuffer::SWReadAccess);
+    QImage imageCopy = m_buffers.back()->asImage()->copy();
+    m_buffers.back()->unlock();
+    return imageCopy;
+}
+
 QPlatformGraphicsBuffer *QCALayerBackingStore::graphicsBuffer() const
 {
     return m_buffers.back().get();