Cocoa: Add QNSView Metal Layer support

Make sure the layer is updated on window resize and
screen change.

Add a support test and print a warning if we try to
create a Metal layer without Metal system support.
This test should ideally be done earlier, before
configuring the QWindow to use Metal.

Link against the Metal framework: The minimum deployment
target is already 10.11 so this does not add additional
deployment requirements.

Change-Id: I0a38e824d0b6042bb52520dfaf0958ce21bb40b8
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

3 files changed, 60 insertions, 3 deletions

diff --git a/src/plugins/platforms/cocoa/cocoa.pro b/src/plugins/platforms/cocoa/cocoa.pro
index 2694cb3607..596b6d8b7f 100644
--- a/src/plugins/platforms/cocoa/cocoa.pro
+++ b/src/plugins/platforms/cocoa/cocoa.pro
@@ -78,7 +78,7 @@ qtConfig(opengl.*) {
 
 RESOURCES += qcocoaresources.qrc
 
-LIBS += -framework AppKit -framework Carbon -framework IOKit -framework QuartzCore -lcups
+LIBS += -framework AppKit -framework Carbon -framework IOKit -framework QuartzCore -framework Metal -lcups
 
 QT += \
     core-private gui-private \
diff --git a/src/plugins/platforms/cocoa/qnsview.h b/src/plugins/platforms/cocoa/qnsview.h
index 100f96d27a..ba696f4b5f 100644
--- a/src/plugins/platforms/cocoa/qnsview.h
+++ b/src/plugins/platforms/cocoa/qnsview.h
@@ -41,6 +41,7 @@
 #define QNSVIEW_H
 
 #include <AppKit/AppKit.h>
+#include <MetalKit/MetalKit.h>
 
 #include "private/qcore_mac_p.h"
 
diff --git a/src/plugins/platforms/cocoa/qnsview_drawing.mm b/src/plugins/platforms/cocoa/qnsview_drawing.mm
index 27224473f1..d2c204deb4 100644
--- a/src/plugins/platforms/cocoa/qnsview_drawing.mm
+++ b/src/plugins/platforms/cocoa/qnsview_drawing.mm
@@ -148,6 +148,53 @@
         "_q_mac_wantsLayer", "QT_MAC_WANTS_LAYER");
 }
 
+- (CALayer *)makeBackingLayer
+{
+    bool makeMetalLayer = false; // TODO: Add/implement enabling API
+    if (makeMetalLayer) {
+        // Check if Metal is supported. If it isn't then it's most likely
+        // too late at this point and the QWindow will be non-functional,
+        // but we can at least print a warning.
+        if (![MTLCreateSystemDefaultDevice() autorelease]) {
+            qWarning() << "QWindow initialization error: Metal is not supported";
+            return [super makeBackingLayer];
+        }
+
+        CAMetalLayer *layer = [CAMetalLayer layer];
+
+        // Set the contentsScale for the layer. This is normally done in
+        // viewDidChangeBackingProperties, however on startup that function
+        // is called before the layer is created here. The layer's drawableSize
+        // is updated from layoutSublayersOfLayer as usual.
+        layer.contentsScale = self.window.backingScaleFactor;
+
+        return layer;
+    }
+
+    return [super makeBackingLayer];
+}
+
+- (NSViewLayerContentsRedrawPolicy)layerContentsRedrawPolicy
+{
+    // We need to set this this excplicitly since the super implementation
+    // returns LayerContentsRedrawNever for custom layers like CAMetalLayer.
+    return NSViewLayerContentsRedrawDuringViewResize;
+}
+
+- (void)updateMetalLayerDrawableSize:(CAMetalLayer *)layer
+{
+    CGSize drawableSize = layer.bounds.size;
+    drawableSize.width *= layer.contentsScale;
+    drawableSize.height *= layer.contentsScale;
+    layer.drawableSize = drawableSize;
+}
+
+- (void)layoutSublayersOfLayer:(CALayer *)layer
+{
+    if ([layer isKindOfClass:CAMetalLayer.class])
+        [self updateMetalLayerDrawableSize:static_cast<CAMetalLayer* >(layer)];
+}
+
 - (void)displayLayer:(CALayer *)layer
 {
     Q_ASSERT(layer == self.layer);
@@ -163,8 +210,17 @@
 
 - (void)viewDidChangeBackingProperties
 {
-    if (self.layer)
-        self.layer.contentsScale = self.window.backingScaleFactor;
+    CALayer *layer = self.layer;
+    if (!layer)
+        return;
+
+    layer.contentsScale = self.window.backingScaleFactor;
+
+    // Metal layers must be manually updated on e.g. screen change
+    if ([layer isKindOfClass:CAMetalLayer.class]) {
+        [self updateMetalLayerDrawableSize:static_cast<CAMetalLayer* >(layer)];
+        [self setNeedsDisplay:YES];
+    }
 }
 
 @end