Add public and QPA APIs for adapting existing OpenGL contexts

For now only xcb on GLX is supported. Other platforms will follow later.

Add also some missing documentation for the platform OpenGL context factory
functions.

[ChangeLog] QOpenGLContext is now able to adopt existing native contexts.

Task-number: QTBUG-37552
Change-Id: I5dd959f102df178f646b2df5989203b5dc6de376
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

6 files changed, 296 insertions, 0 deletions

diff --git a/src/platformheaders/doc/qtplatformheaders.qdocconf b/src/platformheaders/doc/qtplatformheaders.qdocconf
new file mode 100644
index 0000000000..dfef69f892
--- /dev/null
+++ b/src/platformheaders/doc/qtplatformheaders.qdocconf
@@ -0,0 +1,51 @@
+include($QT_INSTALL_DOCS/global/qt-module-defaults.qdocconf)
+
+# Name of the project which must match the outputdir. Determines the .index file
+project = QtPlatformHeaders
+
+# Directories in which to search for files to document and images.
+# By default set to the root directory of the project for sources
+# and headers and qdoc will therefore generate output for each file.
+# Images should be placed in <rootdir>/dic/images and examples in
+# <rootdir>/examples.
+# Paths are relative to the  location of this file.
+
+headerdirs  += ..
+sourcedirs  += ..
+exampledirs += ..
+imagedirs   += images
+
+depends += qtdoc qtcore qtgui qtwidgets
+
+examplesinstallpath     = platformheaders
+
+# The following parameters are for creating a qhp file, the qhelpgenerator
+# program can convert the qhp file into a qch file which can be opened in
+# Qt Assistant and/or Qt Creator.
+
+# Defines the name of the project. You cannot use operators (+, =, -) in
+# the name. Properties for this project are set using a qhp.<projectname>.property
+# format.
+qhp.projects = QtPlatformHeaders
+
+# Sets the name of the output qhp file.
+qhp.QtPlatformHeaders.file = qtplatformheaders.qhp
+
+# Namespace for the output file. This namespace is used to distinguish between
+# different documentation files in Creator/Assistant.
+qhp.QtPlatformHeaders.namespace = org.qt-project.qtplatformheaders.$QT_VERSION_TAG
+
+# Title for the package, will be the main title for the package in
+# Assistant/Creator.
+qhp.QtPlatformHeaders.indexTitle = Qt Platform Headers
+
+# Only update the name of the project for the next variables.
+qhp.QtPlatformHeaders.virtualFolder = qtplatformheaders
+qhp.QtPlatformHeaders.subprojects = classes
+qhp.QtPlatformHeaders.subprojects.classes.title = C++ Classes
+qhp.QtPlatformHeaders.subprojects.classes.indexTitle = Qt Platform Headers C++ Classes
+qhp.QtPlatformHeaders.subprojects.classes.selectors = class fake:headerfile
+qhp.QtPlatformHeaders.subprojects.classes.sortPages = true
+
+navigation.landingpage = "Qt Platform Headers"
+navigation.cppclassespage = "Qt Platform Headers C++ Classes"
diff --git a/src/platformheaders/doc/src/qtplatformheaders.qdoc b/src/platformheaders/doc/src/qtplatformheaders.qdoc
new file mode 100644
index 0000000000..4ed740d296
--- /dev/null
+++ b/src/platformheaders/doc/src/qtplatformheaders.qdoc
@@ -0,0 +1,68 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file.  Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met: http://www.gnu.org/copyleft/fdl.html.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+    \module QtPlatformHeaders
+    \title Qt Platform Headers C++ Classes
+    \ingroup modules
+
+    \brief The Qt Platform Headers module offers header-only inline classes that
+    encapsulate platform-specific information that is tied to a given runtime
+    configuration of a platform plugin.
+*/
+
+/*!
+    \page qtplatformheaders-index.html
+    \title Qt Platform Headers
+
+    \brief The Qt Platform Headers module offers header-only inline classes that
+    encapsulate platform-specific information that is tied to a given runtime
+    configuration of a platform plugin.
+
+    Some applications may need to interface Qt with other frameworks. This often
+    means using graphics contexts or other types of native handles created by
+    one framework with another. For example, on some platforms, QOpenGLContext
+    offers the ability to wrap an existing native OpenGL context, instead of
+    creating a new one. This existing native context can be created by some
+    other third-party code.
+
+    The type of such native handles is highly platform specific and in some
+    cases the platform plugin will need more information to adopt a handle, just
+    the handle in itself will not be sufficient. Therefore the public API
+    consists of functions taking or returning a QVariant that contains a
+    platform-specific value type. See for example
+    QOpenGLContext::setNativeHandle() and QOpenGLContext::nativeHandle(). When
+    running on Linux/X11, using the xcb platform plugin and the GLX windowing
+    system interface, the variant contains a QGLXNativeContext. On other
+    platforms a different class will be used. These classes are all placed in
+    the Qt Platform Headers module.
+
+    \note Similar to the other QPA APIs, there are no binary compatibility
+    guarantees for these classes, meaning that an application using these
+    classes is only guaranteed to work with the Qt version it was developed
+    against. Unlike QPA however, source compatibility is guaranteed.
+ */
diff --git a/src/platformheaders/nativecontexts/nativecontexts.pri b/src/platformheaders/nativecontexts/nativecontexts.pri
new file mode 100644
index 0000000000..dcbeae2b0f
--- /dev/null
+++ b/src/platformheaders/nativecontexts/nativecontexts.pri
@@ -0,0 +1 @@
+HEADERS += $$PWD/qglxnativecontext.h
diff --git a/src/platformheaders/nativecontexts/qglxnativecontext.h b/src/platformheaders/nativecontexts/qglxnativecontext.h
new file mode 100644
index 0000000000..e3dd547a8f
--- /dev/null
+++ b/src/platformheaders/nativecontexts/qglxnativecontext.h
@@ -0,0 +1,82 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the plugins 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/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 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QGLXNATIVECONTEXT_H
+#define QGLXNATIVECONTEXT_H
+
+#include <X11/Xlib.h>
+#include <GL/glx.h>
+
+QT_BEGIN_NAMESPACE
+
+struct QGLXNativeContext
+{
+    QGLXNativeContext()
+        : m_context(0),
+          m_display(0),
+          m_window(0),
+          m_visualId(0)
+    { }
+
+    QGLXNativeContext(GLXContext ctx, Display *dpy = 0, Window wnd = 0, VisualID vid = 0)
+        : m_context(ctx),
+          m_display(dpy),
+          m_window(wnd),
+          m_visualId(vid)
+    { }
+
+    GLXContext context() const { return m_context; }
+    Display *display() const { return m_display; }
+    Window window() const { return m_window; }
+    VisualID visualId() const { return m_visualId; }
+
+private:
+    GLXContext m_context;
+    Display *m_display;
+    Window m_window;
+    VisualID m_visualId;
+};
+
+QT_END_NAMESPACE
+
+Q_DECLARE_METATYPE(QGLXNativeContext)
+
+#endif // QGLXNATIVECONTEXT_H
diff --git a/src/platformheaders/nativecontexts/qglxnativecontext.qdoc b/src/platformheaders/nativecontexts/qglxnativecontext.qdoc
new file mode 100644
index 0000000000..14c6d37c0e
--- /dev/null
+++ b/src/platformheaders/nativecontexts/qglxnativecontext.qdoc
@@ -0,0 +1,83 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:FDL$
+** 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Free Documentation License Usage
+** Alternatively, this file may be used under the terms of the GNU Free
+** Documentation License version 1.3 as published by the Free Software
+** Foundation and appearing in the file included in the packaging of
+** this file.  Please review the following information to ensure
+** the GNU Free Documentation License version 1.3 requirements
+** will be met: http://www.gnu.org/copyleft/fdl.html.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+  \class QGLXNativeContext
+  \inmodule QtPlatformHeaders
+  \since 5.4
+
+  \brief A class encapsulating a GLXContext and related native handles.
+
+  \note Only context() is guaranteed to be valid. The other handles may be all \c 0. They are
+  useful however when QOpenGLContext::setNativeHandle() is used to adopt a legacy context
+  created by glXCreateContext. To adopt such a context, either the Window or VisualID
+  that had been used to create the context needs to be known, otherwise the adoption will
+  fail. For modern contexts created with an FBConfig, these are not necessary, the
+  GLXContext itself is sufficient. The Display is optional.
+
+  \note As of Qt 5.4 there is no binary compatibility guarantee for this class, meaning
+  that an application using it is only guaranteed to work with the Qt version it was
+  developed against.
+
+  \sa QOpenGLContext::setNativeHandle(), QOpenGLContext::nativeHandle()
+ */
+
+/*!
+  \fn GLXContext QGLXNativeContext::context() const
+
+  \return the GLXContext.
+ */
+
+/*!
+  \fn Display *QGLXNativeContext::display() const
+
+  \return a pointer to the X11 display or \c NULL if not available.
+ */
+
+/*!
+  \fn Window QGLXNativeContext::window() const
+
+  \return the X11 Window or \c 0 if not available.
+ */
+
+/*!
+  \fn VisualID QGLXNativeContext::visualId() const
+
+  \return the X11 visual ID or \c 0 if not available.
+ */
+
+/*!
+  \fn QGLXNativeContext::QGLXNativeContext()
+
+  Construct a new instance with no handles.
+ */
+
+/*!
+  \fn QGLXNativeContext::QGLXNativeContext(GLXContext ctx, Display *dpy = 0, Window wnd = 0, VisualID vid = 0)
+
+  Constructs a new instance with the provided \a ctx, \a dpy, \a wnd, \a vid handles.
+ */
diff --git a/src/platformheaders/platformheaders.pro b/src/platformheaders/platformheaders.pro
new file mode 100644
index 0000000000..b243bfa4b5
--- /dev/null
+++ b/src/platformheaders/platformheaders.pro
@@ -0,0 +1,11 @@
+# Only headers here, no library is wanted.
+TEMPLATE = subdirs
+VERSION = $$MODULE_VERSION
+MODULE_INCNAME = QtPlatformHeaders
+
+include(nativecontexts/nativecontexts.pri)
+
+QMAKE_DOCS = $$PWD/doc/qtplatformheaders.qdocconf
+
+load(qt_module_headers)
+load(qt_docs)