macOS: Add QSurfaceType::MetalSurface

Add API to activate previously added Metal layer implementation.
This provides minimal support, and unlike VulkanSurface
there is no separate QWindow subclass.

What this does do is configure the QWindow to use a
Metal layer, and to send expose/update events when
the layer content should be redrawn. Qt will also update
the layer’s drawableSize and contentsScale when needed.

Application code can make use of this by accessing
the QWindow layer, which will be a CAMetalLayer:

  CAMetalLayer *metalLayer = reinterpret_cast<CAMetalLayer *>(
    reinterpret_cast<NSView *>(window->winId()).layer);

Change-Id: I514f5186133c3e610fd4e53ca91fe9c85c6d016e
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/gui/kernel/qsurface.cpp

@@ -80,6 +80,10 @@ QT_BEGIN_NAMESPACE
     in conjunction with OpenVG contexts.
     \value VulkanSurface The surface is a Vulkan compatible surface and can be used
     in conjunction with the Vulkan graphics API.
+    \value MetalSurface The surface is a Metal compatible surface and can be used
+    in conjunction with Apple's Metal graphics API. This surface type is supported
+    on macOS only.
+
  */
 
 

src/gui/kernel/qsurface.h

@@ -66,7 +66,8 @@ public:
         OpenGLSurface,
         RasterGLSurface,
         OpenVGSurface,
-        VulkanSurface
+        VulkanSurface,
+        MetalSurface
     };
 
     virtual ~QSurface();

src/plugins/platforms/cocoa/qnsview_drawing.mm

@@ -133,6 +133,12 @@
     }
 }
 
+- (BOOL)shouldUseMetalLayer:(QSurface::SurfaceType)surfaceType
+{
+    // MetalSurface needs a layer, and so does VulkanSurface (via MoltenVK)
+    return surfaceType == QWindow::MetalSurface || surfaceType == QWindow::VulkanSurface;
+}
+
 - (BOOL)wantsLayer
 {
     Q_ASSERT(m_platformWindow);
@@ -144,16 +150,14 @@
     bool layerRequested = qt_mac_resolveOption(false, m_platformWindow->window(),
         "_q_mac_wantsLayer", "QT_MAC_WANTS_LAYER");
 
-    // Support Vulkan via MoltenVK, which requires a Metal layer
-    bool layerForVulkan = (m_platformWindow->window()->surfaceType() == QWindow::VulkanSurface);
+    bool layerForSurfaceType = [self shouldUseMetalLayer:m_platformWindow->window()->surfaceType()];
 
-    return layerRequested || layerForVulkan;
+    return layerRequested || layerForSurfaceType;
 }
 
 - (CALayer *)makeBackingLayer
 {
-    // Support Vulkan via MoltenVK, which requires a Metal layer
-    bool makeMetalLayer = (m_platformWindow->window()->surfaceType() == QWindow::VulkanSurface);
+    bool makeMetalLayer = [self shouldUseMetalLayer:m_platformWindow->window()->surfaceType()];
     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,

src/plugins/platforms/windows/qwindowsnativeinterface.cpp

@@ -111,15 +111,14 @@ void *QWindowsNativeInterface::nativeResourceForWindow(const QByteArray &resourc
             return 0;
         }
         break;
-    case QWindow::OpenGLSurface:
-    case QWindow::OpenVGSurface:
-        break;
     case QWindow::VulkanSurface:
 #if QT_CONFIG(vulkan)
         if (type == VkSurface)
             return bw->surface(nullptr, nullptr); // returns the address of the VkSurfaceKHR, not the value, as expected
 #endif
         break;
+    default:
+        break;
     }
     qWarning("%s: Invalid key '%s' requested.", __FUNCTION__, resource.constData());
     return 0;