Dynamic GL switch on Windows

The patch introduces a new build configuration on Windows which
can be requested by passing -opengl dynamic to configure.

Platforms other than Windows (including WinRT) are not affected.
The existing Angle and desktop configurations are not affected.
These continue to function as before and Angle remains the default.

In the future, when all modules have added support for the dynamic
path, as described below, the default configuration could be changed
to be the dynamic one. This would allow providing a single set of
binaries in the official builds instead of the current two.

When requesting dynamic GL, Angle is built but QT_OPENGL_ES[_2] are
never defined. Instead, the code path that has traditionally been
desktop GL only becomes the dynamic path that has to do runtime
checks. Qt modules and applications are not linked to opengl32.dll or
libegl/glesv2.dll in this case. Instead, QtGui exports all necessary
egl/egl/gl functions which will, under the hood, forward all requests
to a dynamically loaded EGL/WGL/GL implementation.

Porting guide (better said, changes needed to prepare your code to
work with dynamic GL builds when the fallback to Angle is utilized):

1. In !QT_OPENGL_ES[_2] code branches use QOpenGLFunctions::isES() to
differentiate between desktop and ES where needed. Keep in mind that
it is the desktop GL header (plus qopenglext.h) that is included,
not the GLES one.

QtGui's proxy will handle some differences, for example calling
glClearDepth will route to glClearDepthf when needed. The built-in
eglGetProcAddress is able to retrieve pointers for standard GLES2
functions too so code resolving OpenGL 2 functions will function
in any case.

2. QT_CONFIG will contain "opengl" and "dynamicgl" in dynamic builds,
but never "angle" or "opengles2".

3. The preprocessor define QT_OPENGL_DYNAMIC is also available in
dynamic builds. The usage of this is strongly discouraged and should
not be needed anywhere except for QtGui and the platform plugin.

4. Code in need of the library handle can use
QOpenGLFunctions::platformGLHandle().

The decision on which library to load is currently based on a simple
test that creates a dummy window/context and tries to resolve an
OpenGL 2 function. If this fails, it goes for Angle. This seems to work
well on Win7 PCs for example that do not have proper graphics drivers
providing OpenGL installed but are D3D9 capable using the default drivers.

Setting QT_OPENGL to desktop or angle skips the test and forces
usage of the given GL. There are also two new application attributes
that could be used for the same purpose.

If Angle is requested but the libraries are not present, desktop is
tried. If desktop is requested, or if angle is requested but nothing
works, the EGL/WGL functions will still be callable but will return 0.
This conveniently means that eglInitialize() and such will report a failure.

Debug messages can be enabled by setting QT_OPENGLPROXY_DEBUG. This will
tell which implementation is chosen.

The textures example application is ported to OpenGL 2, the GL 1
code path is removed.

[ChangeLog][QtGui] Qt builds on Windows can now be configured for
dynamic loading of the OpenGL implementation. This can be requested
by passing -opengl dynamic to configure. In this mode no modules will
link to opengl32.dll or Angle's libegl/libglesv2. Instead, QtGui will
dynamically choose between desktop and Angle during the first GL/EGL/WGL
call. This allows deploying applications with a single set of Qt libraries
with the ability of transparently falling back to Angle in case the
opengl32.dll is not suitable, due to missing graphics drivers for example.

Task-number: QTBUG-36483
Change-Id: I716fdebbf60b355b7d9ef57d1e069eef366b4ab9
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

6 files changed, 86 insertions, 59 deletions

diff --git a/src/plugins/platforms/windows/qwindowseglcontext.cpp b/src/plugins/platforms/windows/qwindowseglcontext.cpp
index a8617b2c2b..e025d7e513 100644
--- a/src/plugins/platforms/windows/qwindowseglcontext.cpp
+++ b/src/plugins/platforms/windows/qwindowseglcontext.cpp
@@ -135,11 +135,7 @@ QWindowsEGLContext::~QWindowsEGLContext()
 
 bool QWindowsEGLContext::hasThreadedOpenGLCapability()
 {
-#ifdef QT_OPENGL_ES_2_ANGLE
     return false;
-#else
-    return true;
-#endif
 }
 
 EGLSurface QWindowsEGLContext::eglSurfaceForPlatformSurface(QPlatformSurface *surface)
diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index 8a91929733..e5d9444966 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -43,12 +43,20 @@
 #include "qwindowsintegration.h"
 #include "qwindowswindow.h"
 #include "qwindowscontext.h"
-#if defined(QT_OPENGL_ES_2)
+
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
 #  include "qwindowseglcontext.h"
 #  include <QtGui/QOpenGLContext>
-#elif !defined(QT_NO_OPENGL)
+#endif
+
+#if !defined(QT_NO_OPENGL) && !defined(QT_OPENGL_ES_2)
 #  include "qwindowsglcontext.h"
 #endif
+
+#if !defined(QT_NO_OPENGL)
+#  include <QtGui/QOpenGLFunctions>
+#endif
+
 #include "qwindowsscreen.h"
 #include "qwindowstheme.h"
 #include "qwindowsservices.h"
@@ -125,9 +133,10 @@ QT_BEGIN_NAMESPACE
 
 struct QWindowsIntegrationPrivate
 {
-#if defined(QT_OPENGL_ES_2)
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
     typedef QSharedPointer<QWindowsEGLStaticContext> QEGLStaticContextPtr;
-#elif !defined(QT_NO_OPENGL)
+#endif
+#if !defined(QT_NO_OPENGL) && !defined(QT_OPENGL_ES_2)
     typedef QSharedPointer<QOpenGLStaticContext> QOpenGLStaticContextPtr;
 #endif
 
@@ -143,9 +152,10 @@ struct QWindowsIntegrationPrivate
     QWindowsDrag m_drag;
 #  endif
 #endif
-#if defined(QT_OPENGL_ES_2)
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
     QEGLStaticContextPtr m_staticEGLContext;
-#elif !defined(QT_NO_OPENGL)
+#endif
+#if !defined(QT_NO_OPENGL) && !defined(QT_OPENGL_ES_2)
     QOpenGLStaticContextPtr m_staticOpenGLContext;
 #endif
     QWindowsInputContext m_inputContext;
@@ -216,8 +226,8 @@ bool QWindowsIntegration::hasCapability(QPlatformIntegration::Capability cap) co
     case OpenGL:
         return true;
     case ThreadedOpenGL:
-#  ifdef QT_OPENGL_ES_2
-        return QWindowsEGLContext::hasThreadedOpenGLCapability();
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
+        return QOpenGLFunctions::isES() ? QWindowsEGLContext::hasThreadedOpenGLCapability() : true;
 #  else
         return true;
 #  endif // QT_OPENGL_ES_2
@@ -278,23 +288,27 @@ QPlatformOpenGLContext
     *QWindowsIntegration::createPlatformOpenGLContext(QOpenGLContext *context) const
 {
     qCDebug(lcQpaGl) << __FUNCTION__ << context->format();
-#ifdef QT_OPENGL_ES_2
-    if (d->m_staticEGLContext.isNull()) {
-        QWindowsEGLStaticContext *staticContext = QWindowsEGLStaticContext::create();
-        if (!staticContext)
-            return 0;
-        d->m_staticEGLContext = QSharedPointer<QWindowsEGLStaticContext>(staticContext);
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
+    if (QOpenGLFunctions::isES()){
+        if (d->m_staticEGLContext.isNull()) {
+            QWindowsEGLStaticContext *staticContext = QWindowsEGLStaticContext::create();
+            if (!staticContext)
+                return 0;
+            d->m_staticEGLContext = QSharedPointer<QWindowsEGLStaticContext>(staticContext);
+        }
+        return new QWindowsEGLContext(d->m_staticEGLContext, context->format(), context->shareHandle());
+    }
+#endif
+#if !defined(QT_OPENGL_ES_2)
+    if (!QOpenGLFunctions::isES()) {
+        if (d->m_staticOpenGLContext.isNull())
+            d->m_staticOpenGLContext =
+                QSharedPointer<QOpenGLStaticContext>(QOpenGLStaticContext::create());
+        QScopedPointer<QWindowsGLContext> result(new QWindowsGLContext(d->m_staticOpenGLContext, context));
+        return result->isValid() ? result.take() : 0;
     }
-    return new QWindowsEGLContext(d->m_staticEGLContext, context->format(), context->shareHandle());
-#else  // QT_OPENGL_ES_2
-    if (d->m_staticOpenGLContext.isNull())
-        d->m_staticOpenGLContext =
-            QSharedPointer<QOpenGLStaticContext>(QOpenGLStaticContext::create());
-    QScopedPointer<QWindowsGLContext> result(new QWindowsGLContext(d->m_staticOpenGLContext, context));
-    if (result->isValid())
-        return result.take();
-    return 0;
 #endif // !QT_OPENGL_ES_2
+    return 0;
 }
 #endif // !QT_NO_OPENGL
 
diff --git a/src/plugins/platforms/windows/qwindowsnativeinterface.cpp b/src/plugins/platforms/windows/qwindowsnativeinterface.cpp
index 9bf4b3240c..fb1b63084f 100644
--- a/src/plugins/platforms/windows/qwindowsnativeinterface.cpp
+++ b/src/plugins/platforms/windows/qwindowsnativeinterface.cpp
@@ -43,13 +43,19 @@
 #include "qwindowswindow.h"
 #include "qwindowscontext.h"
 
-#if defined(QT_OPENGL_ES_2)
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
 #  include "qwindowseglcontext.h"
 #  include <QtGui/QOpenGLContext>
-#elif !defined(QT_NO_OPENGL)
+#endif
+
+#if !defined(QT_NO_OPENGL) && !defined(QT_OPENGL_ES_2)
 #  include "qwindowsglcontext.h"
 #endif
 
+#if !defined(QT_NO_OPENGL)
+#  include <QtGui/QOpenGLFunctions>
+#endif
+
 #include <QtGui/QWindow>
 
 QT_BEGIN_NAMESPACE
@@ -113,19 +119,24 @@ void *QWindowsNativeInterface::nativeResourceForContext(const QByteArray &resour
         qWarning("%s: '%s' requested for null context or context without handle.", __FUNCTION__, resource.constData());
         return 0;
     }
-#ifdef QT_OPENGL_ES_2
-    QWindowsEGLContext *windowsEglContext = static_cast<QWindowsEGLContext *>(context->handle());
-    if (resource == QByteArrayLiteral("eglDisplay"))
-        return windowsEglContext->eglDisplay();
-    if (resource == QByteArrayLiteral("eglContext"))
-        return windowsEglContext->eglContext();
-    if (resource == QByteArrayLiteral("eglConfig"))
-        return windowsEglContext->eglConfig();
-#else // QT_OPENGL_ES_2
-    QWindowsGLContext *windowsContext = static_cast<QWindowsGLContext *>(context->handle());
-    if (resource == QByteArrayLiteral("renderingContext"))
-        return windowsContext->renderingContext();
-#endif // !QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
+    if (QOpenGLFunctions::isES()) {
+        QWindowsEGLContext *windowsEglContext = static_cast<QWindowsEGLContext *>(context->handle());
+        if (resource == QByteArrayLiteral("eglDisplay"))
+            return windowsEglContext->eglDisplay();
+        if (resource == QByteArrayLiteral("eglContext"))
+            return windowsEglContext->eglContext();
+        if (resource == QByteArrayLiteral("eglConfig"))
+            return windowsEglContext->eglConfig();
+    }
+#endif // QT_OPENGL_ES_2 || QT_OPENGL_DYNAMIC
+#if !defined(QT_OPENGL_ES_2)
+    if (!QOpenGLFunctions::isES()) {
+        QWindowsGLContext *windowsContext = static_cast<QWindowsGLContext *>(context->handle());
+        if (resource == QByteArrayLiteral("renderingContext"))
+            return windowsContext->renderingContext();
+    }
+#endif // QT_OPENGL_ES_2 || QT_OPENGL_DYNAMIC
 
     qWarning("%s: Invalid key '%s' requested.", __FUNCTION__, resource.constData());
     return 0;
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 256967d25f..a0a9e75e2d 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -48,8 +48,9 @@
 #  include "qwindowscursor.h"
 #endif
 
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
 #  include "qwindowseglcontext.h"
+#  include <QtGui/QOpenGLFunctions>
 #endif
 
 #include <QtGui/QGuiApplication>
@@ -861,7 +862,7 @@ QWindowsWindow::QWindowsWindow(QWindow *aWindow, const QWindowsWindowData &data)
     m_dropTarget(0),
     m_savedStyle(0),
     m_format(aWindow->format()),
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
     m_eglSurface(0),
 #endif
 #ifdef Q_OS_WINCE
@@ -878,8 +879,9 @@ QWindowsWindow::QWindowsWindow(QWindow *aWindow, const QWindowsWindowData &data)
         return; // No further handling for Qt::Desktop
     if (aWindow->surfaceType() == QWindow::OpenGLSurface) {
         setFlag(OpenGLSurface);
-#ifdef QT_OPENGL_ES_2
-        setFlag(OpenGL_ES2);
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
+        if (QOpenGLFunctions::isES())
+            setFlag(OpenGL_ES2);
 #endif
     }
     updateDropSite();
@@ -933,7 +935,7 @@ void QWindowsWindow::destroyWindow()
         if (hasMouseCapture())
             setMouseGrabEnabled(false);
         setDropSiteEnabled(false);
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
         if (m_eglSurface) {
             qCDebug(lcQpaGl) << __FUNCTION__ << "Freeing EGL surface " << m_eglSurface << window();
             eglDestroySurface(m_staticEglContext->display(), m_eglSurface);
@@ -2107,7 +2109,7 @@ void QWindowsWindow::setEnabled(bool enabled)
         setStyle(newStyle);
 }
 
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
 EGLSurface QWindowsWindow::ensureEglSurfaceHandle(const QWindowsWindow::QWindowsEGLStaticContextPtr &staticContext, EGLConfig config)
 {
     if (!m_eglSurface) {
diff --git a/src/plugins/platforms/windows/qwindowswindow.h b/src/plugins/platforms/windows/qwindowswindow.h
index 1d515fd2fe..ba0f22bb0a 100644
--- a/src/plugins/platforms/windows/qwindowswindow.h
+++ b/src/plugins/platforms/windows/qwindowswindow.h
@@ -50,7 +50,7 @@
 
 #include <qpa/qplatformwindow.h>
 
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
 #  include <QtCore/QSharedPointer>
 #  include <EGL/egl.h>
 #endif
@@ -60,7 +60,7 @@ QT_BEGIN_NAMESPACE
 class QWindowsOleDropTarget;
 class QDebug;
 
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
 class QWindowsEGLStaticContext;
 #endif
 
@@ -130,7 +130,7 @@ struct QWindowsWindowData
 class QWindowsWindow : public QPlatformWindow
 {
 public:
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
     typedef QSharedPointer<QWindowsEGLStaticContext> QWindowsEGLStaticContextPtr;
 #endif
 
@@ -206,7 +206,7 @@ public:
     QMargins customMargins() const { return m_data.customMargins; }
     void setCustomMargins(const QMargins &m);
 
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
     EGLSurface eglSurfaceHandle() const { return m_eglSurface;}
     EGLSurface ensureEglSurfaceHandle(const QWindowsEGLStaticContextPtr &staticContext, EGLConfig config);
 #endif
@@ -301,7 +301,7 @@ private:
     unsigned m_savedStyle;
     QRect m_savedFrameGeometry;
     const QSurfaceFormat m_format;
-#ifdef QT_OPENGL_ES_2
+#if defined(QT_OPENGL_ES_2) || defined(QT_OPENGL_DYNAMIC)
     EGLSurface m_eglSurface;
     QSharedPointer<QWindowsEGLStaticContext> m_staticEglContext;
 #endif
diff --git a/src/plugins/platforms/windows/windows.pri b/src/plugins/platforms/windows/windows.pri
index c10d00c2ad..13799ba1ba 100644
--- a/src/plugins/platforms/windows/windows.pri
+++ b/src/plugins/platforms/windows/windows.pri
@@ -2,7 +2,7 @@
 LIBS *= -lole32
 !wince*:LIBS *= -luser32 -lwinspool -limm32 -lwinmm  -loleaut32
 
-contains(QT_CONFIG, opengl):!contains(QT_CONFIG, opengles2):LIBS *= -lopengl32
+contains(QT_CONFIG, opengl):!contains(QT_CONFIG, opengles2):!contains(QT_CONFIG, dynamicgl): LIBS *= -lopengl32
 
 mingw: LIBS *= -luuid
 # For the dialog helpers:
@@ -71,11 +71,15 @@ INCLUDEPATH += $$PWD
 contains(QT_CONFIG, opengles2) {
     SOURCES += $$PWD/qwindowseglcontext.cpp
     HEADERS += $$PWD/qwindowseglcontext.h
-} else {
-    contains(QT_CONFIG, opengl) {
-        SOURCES += $$PWD/qwindowsglcontext.cpp
-        HEADERS += $$PWD/qwindowsglcontext.h
-   }
+} else: contains(QT_CONFIG,opengl) {
+    SOURCES += $$PWD/qwindowsglcontext.cpp
+    HEADERS += $$PWD/qwindowsglcontext.h
+}
+
+# Dynamic GL needs both WGL and EGL
+contains(QT_CONFIG,dynamicgl) {
+    SOURCES += $$PWD/qwindowseglcontext.cpp
+    HEADERS += $$PWD/qwindowseglcontext.h
 }
 
 !contains( DEFINES, QT_NO_CLIPBOARD ) {