macOS: Restore support for layered mode

After 871966 we now do drawing as a result of drawRect calls, but layer
backed mode was not taken into account. This restores support for both
pull and push-mode drawing in layer-backed mode.

Change-Id: I35039ee9eb4486206f9f92f8230df104473368c9
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/cocoa/qcocoabackingstore.h

@@ -42,6 +42,8 @@
 
 #include <QtGraphicsSupport/private/qrasterbackingstore_p.h>
 
+#include <private/qcore_mac_p.h>
+
 QT_BEGIN_NAMESPACE
 
 class QCocoaBackingStore : public QRasterBackingStore
@@ -50,12 +52,16 @@ public:
     QCocoaBackingStore(QWindow *window);
     ~QCocoaBackingStore();
 
+    void beginPaint(const QRegion &) override;
+    void endPaint() override;
+
     void flush(QWindow *, const QRegion &, const QPoint &) Q_DECL_OVERRIDE;
 
 private:
     bool windowHasUnifiedToolbar() const;
     QImage::Format format() const Q_DECL_OVERRIDE;
     void redrawRoundedBottomCorners(CGRect) const;
+    QCFType<CGImageRef> m_cgImage;
 };
 
 QT_END_NAMESPACE

src/plugins/platforms/cocoa/qcocoabackingstore.mm

@@ -48,6 +48,7 @@ Q_LOGGING_CATEGORY(lcCocoaBackingStore, "qt.qpa.cocoa.backingstore");
 
 QCocoaBackingStore::QCocoaBackingStore(QWindow *window)
     : QRasterBackingStore(window)
+    , m_cgImage(nullptr)
 {
 }
 
@@ -69,6 +70,18 @@ QImage::Format QCocoaBackingStore::format() const
     return QRasterBackingStore::format();
 }
 
+void QCocoaBackingStore::beginPaint(const QRegion &region)
+{
+    m_cgImage = nullptr;
+    QRasterBackingStore::beginPaint(region);
+}
+
+void QCocoaBackingStore::endPaint()
+{
+    QRasterBackingStore::endPaint();
+    m_cgImage = m_image.toCGImage();
+}
+
 #if !QT_MACOS_PLATFORM_SDK_EQUAL_OR_ABOVE(__MAC_10_12)
 static const NSCompositingOperation NSCompositingOperationCopy = NSCompositeCopy;
 static const NSCompositingOperation NSCompositingOperationSourceOver = NSCompositeSourceOver;
@@ -107,6 +120,25 @@ void QCocoaBackingStore::flush(QWindow *window, const QRegion &region, const QPo
         qCDebug(lcCocoaBackingStore) << "Flushing" << region << "of" << view << qPrintable(targetViewDescription);
     }
 
+    if (view.layer) {
+        // In layer-backed mode, locking focus on a view does not give the right
+        // view transformation, and doesn't give us a graphics context to render
+        // via when drawing outside of the display cycle. Instead we tell AppKit
+        // that we want to update the layer's content, via [NSView wantsUpdateLayer],
+        // which result in AppKit not creating a backingstore for each layer, and
+        // we then directly set the layer's backingstore (content) to our backingstore,
+        // masked to the part of the subview that is relevant.
+        // FIXME: Figure out if there's a way to do partial updates
+        view.layer.contents = (__bridge id)static_cast<CGImageRef>(m_cgImage);
+        if (view != topLevelView) {
+            view.layer.contentsRect = CGRectApplyAffineTransform(
+                [view convertRect:view.bounds toView:topLevelView],
+                // The contentsRect is in unit coordinate system
+                CGAffineTransformMakeScale(1.0 / m_image.width(), 1.0 / m_image.height()));
+        }
+        return;
+    }
+
     // Normally a NSView is drawn via drawRect, as part of the display cycle in the
     // main runloop, via setNeedsDisplay and friends. AppKit will lock focus on each
     // individual view, starting with the top level and then traversing any subviews,
@@ -156,8 +188,7 @@ void QCocoaBackingStore::flush(QWindow *window, const QRegion &region, const QPo
         "Focusing the view should give us a current graphics context");
 
     // Create temporary image to use for blitting, without copying image data
-    NSImage *backingStoreImage = [[[NSImage alloc]
-        initWithCGImage:QCFType<CGImageRef>(m_image.toCGImage()) size:NSZeroSize] autorelease];
+    NSImage *backingStoreImage = [[[NSImage alloc] initWithCGImage:m_cgImage size:NSZeroSize] autorelease];
 
     if ([topLevelView hasMask]) {
         // FIXME: Implement via NSBezierPath and addClip

src/plugins/platforms/cocoa/qnsview.mm

@@ -384,6 +384,22 @@ static QTouchDevice *touchDevice = 0;
     m_platformWindow->handleExposeEvent(exposedRegion);
 }
 
+- (BOOL)wantsUpdateLayer
+{
+    return YES;
+}
+
+- (void)updateLayer
+{
+    if (!m_platformWindow)
+        return;
+
+    qCDebug(lcQpaCocoaWindow) << "[QNSView updateLayer]" << m_platformWindow->window();
+
+    // FIXME: Find out if there's a way to resolve the dirty rect like in drawRect:
+    m_platformWindow->handleExposeEvent(QRectF::fromCGRect(self.bounds).toRect());
+}
+
 - (BOOL)isFlipped
 {
     return YES;