macOS: Add support for non-window backed offscreen surfaces

The modern approach to offscreen rendering on macOS is via FBOs, which
means there's no reason to allocate an NSView and corresponding NSWindow
just for that. In the offscreen case the NSOpenGLContext has a nil-view.

Change-Id: I2d1d407069af4d5283e6f56fba83db8eaf694ac6
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

3 files changed, 27 insertions, 2 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoaglcontext.mm b/src/plugins/platforms/cocoa/qcocoaglcontext.mm
index 75ac348802..5ed81a7f1b 100644
--- a/src/plugins/platforms/cocoa/qcocoaglcontext.mm
+++ b/src/plugins/platforms/cocoa/qcocoaglcontext.mm
@@ -218,6 +218,9 @@ void QCocoaGLContext::windowWasHidden()
 
 void QCocoaGLContext::swapBuffers(QPlatformSurface *surface)
 {
+    if (surface->surface()->surfaceClass() == QSurface::Offscreen)
+        return; // Nothing to do
+
     QWindow *window = static_cast<QCocoaWindow *>(surface)->window();
     setActiveWindow(window);
 
@@ -229,11 +232,13 @@ bool QCocoaGLContext::makeCurrent(QPlatformSurface *surface)
     Q_ASSERT(surface->surface()->supportsOpenGL());
 
     QMacAutoReleasePool pool;
+    [m_context makeCurrentContext];
+
+    if (surface->surface()->surfaceClass() == QSurface::Offscreen)
+        return true;
 
     QWindow *window = static_cast<QCocoaWindow *>(surface)->window();
     setActiveWindow(window);
-
-    [m_context makeCurrentContext];
     update();
     return true;
 }
diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.h b/src/plugins/platforms/cocoa/qcocoaintegration.h
index 8745b6a4e3..dc7c5916a3 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.h
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.h
@@ -77,6 +77,7 @@ public:
     bool hasCapability(QPlatformIntegration::Capability cap) const Q_DECL_OVERRIDE;
     QPlatformWindow *createPlatformWindow(QWindow *window) const Q_DECL_OVERRIDE;
     QPlatformWindow *createForeignWindow(QWindow *window, WId nativeHandle) const Q_DECL_OVERRIDE;
+    QPlatformOffscreenSurface *createPlatformOffscreenSurface(QOffscreenSurface *surface) const override;
 #ifndef QT_NO_OPENGL
     QPlatformOpenGLContext *createPlatformOpenGLContext(QOpenGLContext *context) const Q_DECL_OVERRIDE;
 #endif
diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.mm b/src/plugins/platforms/cocoa/qcocoaintegration.mm
index 61eeeaf436..dd17848109 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.mm
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.mm
@@ -56,6 +56,7 @@
 #include <qpa/qplatforminputcontextfactory_p.h>
 #include <qpa/qplatformaccessibility.h>
 #include <qpa/qplatforminputcontextfactory_p.h>
+#include <qpa/qplatformoffscreensurface.h>
 #include <QtCore/qcoreapplication.h>
 
 #include <QtGui/private/qcoregraphics_p.h>
@@ -331,6 +332,24 @@ QPlatformWindow *QCocoaIntegration::createForeignWindow(QWindow *window, WId nat
     return new QCocoaWindow(window, nativeHandle);
 }
 
+class QCocoaOffscreenSurface : public QPlatformOffscreenSurface
+{
+public:
+    QCocoaOffscreenSurface(QOffscreenSurface *offscreenSurface) : QPlatformOffscreenSurface(offscreenSurface) {}
+
+    QSurfaceFormat format() const override
+    {
+        Q_ASSERT(offscreenSurface());
+        return offscreenSurface()->requestedFormat();
+    }
+    bool isValid() const override { return true; }
+};
+
+QPlatformOffscreenSurface *QCocoaIntegration::createPlatformOffscreenSurface(QOffscreenSurface *surface) const
+{
+    return new QCocoaOffscreenSurface(surface);
+}
+
 #ifndef QT_NO_OPENGL
 QPlatformOpenGLContext *QCocoaIntegration::createPlatformOpenGLContext(QOpenGLContext *context) const
 {