Introduce platform API abstraction for QOpenGLContext

The API is available by including qopenglcontext.h as usual,
but scoped in the QPlatformInterface namespace. The namespace
exposes platform specific type-safe interfaces that provide:

 a) Factory functions for adopting native contexts, e.g.

    QCocoaGLContext::fromNative(nsContext, shareContext);

 b) Access to underlying native handles, e.g.

    openGLContext->platformInterface<QCocoaGLContext>->nativeContext()

 c) Platform specific functionality, e.g.

    static QWGLContext::openGLModuleHandle()

    openGLContext->platformInterface<QEGLContext>->doSomething();

The platform interfaces live close to the classes they extend,
removing the need for complex indirection and plumbing, and
avoids kitchen-sink modules and APIs such as the extras modules,
QPlatformFunctions, or QPlatformNativeInterface.

In the case of QOpenGLContext these platform APIs are backed
by the platform plugin, so dynamic_cast is used to ensure the
platform plugin supports the requested interface, but this is
and implementation detail. The interface APIs are agnostic
to where the implementation lives, while still being available
to the user as part of the APIs they extend/augment.

The documentation will be restored when the dust settles.

Task-number: QTBUG-80233
Change-Id: Iac612403383991c4b24064332542a6e4bcbb3293
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

7 files changed, 214 insertions, 2 deletions

diff --git a/src/gui/platform/macos/macos.pri b/src/gui/platform/macos/macos.pri
new file mode 100644
index 0000000000..f0107c6944
--- /dev/null
+++ b/src/gui/platform/macos/macos.pri
@@ -0,0 +1,4 @@
+SOURCES += \
+    $$PWD/qcocoaplatforminterface.mm
+
+LIBS_PRIVATE += -framework AppKit
diff --git a/src/gui/platform/macos/qcocoaplatforminterface.mm b/src/gui/platform/macos/qcocoaplatforminterface.mm
new file mode 100644
index 0000000000..a1410a63b2
--- /dev/null
+++ b/src/gui/platform/macos/qcocoaplatforminterface.mm
@@ -0,0 +1,60 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtGui module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtGui/private/qopenglcontext_p.h>
+#include <QtGui/private/qguiapplication_p.h>
+#include <qpa/qplatformopenglcontext.h>
+#include <qpa/qplatformintegration.h>
+
+#include <AppKit/AppKit.h>
+
+QT_BEGIN_NAMESPACE
+
+using namespace QPlatformInterface::Private;
+
+QT_DEFINE_PLATFORM_INTERFACE(QCocoaGLContext, QOpenGLContext);
+QT_DEFINE_PRIVATE_PLATFORM_INTERFACE(QCocoaGLIntegration);
+
+QOpenGLContext *QPlatformInterface::QCocoaGLContext::fromNative(NSOpenGLContext *nativeContext, QOpenGLContext *shareContext)
+{
+    return QGuiApplicationPrivate::platformIntegration()->call<
+        &QCocoaGLIntegration::createOpenGLContext>(nativeContext, shareContext);
+}
+
+QT_END_NAMESPACE
diff --git a/src/gui/platform/platform.pri b/src/gui/platform/platform.pri
index 14a10d10b1..71cffb403e 100644
--- a/src/gui/platform/platform.pri
+++ b/src/gui/platform/platform.pri
@@ -2,3 +2,4 @@ wasm:include(wasm/wasm.pri)
 darwin:include(darwin/darwin.pri)
 win32:include(windows/windows.pri)
 unix:include(unix/unix.pri)
+macos:include(macos/macos.pri)
diff --git a/src/gui/platform/unix/qunixplatforminterface.cpp b/src/gui/platform/unix/qunixplatforminterface.cpp
new file mode 100644
index 0000000000..a090ef6601
--- /dev/null
+++ b/src/gui/platform/unix/qunixplatforminterface.cpp
@@ -0,0 +1,80 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtGui module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtGui/private/qtguiglobal_p.h>
+
+#include <QtGui/private/qopenglcontext_p.h>
+#include <QtGui/private/qguiapplication_p.h>
+
+#include <qpa/qplatformopenglcontext.h>
+#include <qpa/qplatformintegration.h>
+
+QT_BEGIN_NAMESPACE
+
+using namespace QPlatformInterface::Private;
+
+#if defined(Q_OS_LINUX)
+QT_DEFINE_PLATFORM_INTERFACE(QGLXContext, QOpenGLContext);
+QT_DEFINE_PRIVATE_PLATFORM_INTERFACE(QGLXIntegration);
+
+QOpenGLContext *QPlatformInterface::QGLXContext::fromNative(GLXContext configBasedContext, QOpenGLContext *shareContext)
+{
+    return QGuiApplicationPrivate::platformIntegration()->call<
+        &QGLXIntegration::createOpenGLContext>(configBasedContext, nullptr, shareContext);
+}
+
+QOpenGLContext *QPlatformInterface::QGLXContext::fromNative(GLXContext visualBasedContext, void *visualInfo, QOpenGLContext *shareContext)
+{
+    return QGuiApplicationPrivate::platformIntegration()->call<
+        &QGLXIntegration::createOpenGLContext>(visualBasedContext, visualInfo, shareContext);
+}
+#endif
+
+#if QT_CONFIG(egl)
+QT_DEFINE_PLATFORM_INTERFACE(QEGLContext, QOpenGLContext);
+QT_DEFINE_PRIVATE_PLATFORM_INTERFACE(QEGLIntegration);
+
+QOpenGLContext *QPlatformInterface::QEGLContext::fromNative(EGLContext context, EGLDisplay display, QOpenGLContext *shareContext)
+{
+    return QGuiApplicationPrivate::platformIntegration()->call<
+        &QEGLIntegration::createOpenGLContext>(context, display, shareContext);
+}
+#endif
+
+QT_END_NAMESPACE
diff --git a/src/gui/platform/unix/unix.pri b/src/gui/platform/unix/unix.pri
index 82eb63b11b..b12f3147a3 100644
--- a/src/gui/platform/unix/unix.pri
+++ b/src/gui/platform/unix/unix.pri
@@ -1,6 +1,7 @@
 SOURCES += \
     platform/unix/qunixeventdispatcher.cpp \
-    platform/unix/qgenericunixeventdispatcher.cpp
+    platform/unix/qgenericunixeventdispatcher.cpp \
+    platform/unix/qunixplatforminterface.cpp
 
 HEADERS += \
     platform/unix/qunixeventdispatcher_qpa_p.h \
diff --git a/src/gui/platform/windows/qwindowsplatforminterface.cpp b/src/gui/platform/windows/qwindowsplatforminterface.cpp
new file mode 100644
index 0000000000..ceb65cda5b
--- /dev/null
+++ b/src/gui/platform/windows/qwindowsplatforminterface.cpp
@@ -0,0 +1,64 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtGui module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtGui/qopenglcontext.h>
+#include <QtGui/private/qguiapplication_p.h>
+#include <qpa/qplatformopenglcontext.h>
+#include <qpa/qplatformintegration.h>
+
+QT_BEGIN_NAMESPACE
+
+using namespace QPlatformInterface::Private;
+
+QT_DEFINE_PLATFORM_INTERFACE(QWGLContext, QOpenGLContext);
+QT_DEFINE_PRIVATE_PLATFORM_INTERFACE(QWindowsGLIntegration);
+
+HMODULE QPlatformInterface::QWGLContext::openGLModuleHandle()
+{
+    return QGuiApplicationPrivate::platformIntegration()->call<
+        &QWindowsGLIntegration::openGLModuleHandle>();
+}
+
+QOpenGLContext *QPlatformInterface::QWGLContext::fromNative(HGLRC context, HWND window, QOpenGLContext *shareContext)
+{
+    return QGuiApplicationPrivate::platformIntegration()->call<
+        &QWindowsGLIntegration::createOpenGLContext>(context, window, shareContext);
+}
+
+QT_END_NAMESPACE
diff --git a/src/gui/platform/windows/windows.pri b/src/gui/platform/windows/windows.pri
index 809576ab31..b1e80f6538 100644
--- a/src/gui/platform/windows/windows.pri
+++ b/src/gui/platform/windows/windows.pri
@@ -1,2 +1,4 @@
 HEADERS += platform/windows/qwindowsguieventdispatcher_p.h
-SOURCES += platform/windows/qwindowsguieventdispatcher.cpp
+SOURCES += \
+    platform/windows/qwindowsguieventdispatcher.cpp \
+    platform/windows/qwindowsplatforminterface.cpp