Introduced QOpenGLContext::defaultFramebufferObject().

Also add some debugging helpers to make sure applications are correctly
written even on less restrictive platforms.

Change-Id: Ie92e497c32e07b2b83662f7ab5540d8f37777fd0
Reviewed-by: Jørgen Lind <jorgen.lind@nokia.com>

src/gui/kernel/qopenglcontext.cpp

@@ -68,6 +68,11 @@ public:
 
 static QThreadStorage<QGuiGLThreadContext *> qwindow_context_storage;
 
+#ifndef QT_NO_DEBUG
+QHash<QOpenGLContext *, bool> QOpenGLContextPrivate::makeCurrentTracker;
+QMutex QOpenGLContextPrivate::makeCurrentTrackerMutex;
+#endif
+
 void QOpenGLContextPrivate::setCurrentContext(QOpenGLContext *context)
 {
     QGuiGLThreadContext *threadContext = qwindow_context_storage.localData();
@@ -204,6 +209,10 @@ void QOpenGLContext::destroy()
 QOpenGLContext::~QOpenGLContext()
 {
     destroy();
+
+#ifndef QT_NO_DEBUG
+    QOpenGLContextPrivate::cleanMakeCurrentTracker(this);
+#endif
 }
 
 /*!
@@ -229,6 +238,29 @@ QOpenGLFunctions *QOpenGLContext::functions() const
     return d->functions;
 }
 
+/*!
+  Call this to get the default framebuffer object for the current surface.
+
+  On some platforms the default framebuffer object depends on the surface being rendered to,
+  and might be different from 0. Thus, instead of calling glBindFramebuffer(0), you should
+  call glBindFramebuffer(ctx->defaultFramebufferObject()) if you want your application to
+  work across different Qt platforms.
+
+  If you use the glBindFramebuffer() in QOpenGLFunctions you do not have to worry about this,
+  as it automatically binds the current context's defaultFramebufferObject() when 0 is passed.
+*/
+GLuint QOpenGLContext::defaultFramebufferObject() const
+{
+    if (!isValid())
+        return 0;
+
+    Q_D(const QOpenGLContext);
+    if (!d->surface || !d->surface->surfaceHandle())
+        return 0;
+
+    return d->platformGLContext->defaultFramebufferObject(d->surface->surfaceHandle());
+}
+
 /*!
   If surface is 0 this is equivalent to calling doneCurrent().
 
@@ -260,6 +292,10 @@ bool QOpenGLContext::makeCurrent(QSurface *surface)
 
         d->shareGroup->d_func()->deletePendingResources(this);
 
+#ifndef QT_NO_DEBUG
+        QOpenGLContextPrivate::toggleMakeCurrentTracker(this, true);
+#endif
+
         return true;
     }
 
@@ -294,6 +330,17 @@ QSurface *QOpenGLContext::surface() const
 }
 
 
+/*!
+    Swap the back and front buffers of the given surface.
+
+    Call this to finish a frame of OpenGL rendering, and make sure to
+    call makeCurrent() again before you begin a new frame.
+
+    If you have bound a non-default framebuffer object, you need to
+    use bindDefaultFramebufferObject() to make sure that the default
+    framebuffer object is bound before calling swapBuffers(), as
+    some Qt platforms assume that the default framebuffer object is bound.
+*/
 void QOpenGLContext::swapBuffers(QSurface *surface)
 {
     Q_D(QOpenGLContext);
@@ -306,8 +353,28 @@ void QOpenGLContext::swapBuffers(QSurface *surface)
     }
 
     QPlatformSurface *surfaceHandle = surface->surfaceHandle();
-    if (surfaceHandle)
+    if (!surfaceHandle)
-        d->platformGLContext->swapBuffers(surfaceHandle);
+        return;
+
+#if !defined(QT_NO_DEBUG)
+    if (currentContext() != this)
+        qWarning() << "QOpenGLContext::swapBuffers() called with non-current surface";
+    else if (!QOpenGLContextPrivate::toggleMakeCurrentTracker(this, false))
+        qWarning() << "QOpenGLContext::swapBuffers() called without corresponding makeCurrent()";
+
+#ifndef GL_FRAMEBUFFER_BINDING
+#define GL_FRAMEBUFFER_BINDING 0x8CA6
+#endif
+
+    GLint framebufferBinding = 0;
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &framebufferBinding);
+
+    GLint platformFramebuffer = GLint(d->platformGLContext->defaultFramebufferObject(surfaceHandle));
+    if (framebufferBinding != platformFramebuffer)
+        qWarning() << "QOpenGLContext::swapBuffers() called with non-default framebuffer object bound";
+#endif
+
+    d->platformGLContext->swapBuffers(surfaceHandle);
 }
 
 QFunctionPointer QOpenGLContext::getProcAddress(const QByteArray &procName)

src/gui/kernel/qopenglcontext.h

@@ -50,11 +50,17 @@
 
 #include <QtGui/QSurfaceFormat>
 
+#ifdef __GLEW_H__
+#warning qopenglfunctions.h is not compatible with GLEW, GLEW defines will be undefined
+#warning To use GLEW with Qt, do not include <qopengl.h> or <QOpenGLFunctions> after glew.h
+#endif
+
+#include <QtGui/qopengl.h>
+
 QT_BEGIN_HEADER
 
 QT_BEGIN_NAMESPACE
 
-
 class QOpenGLContextPrivate;
 class QOpenGLContextGroupPrivate;
 class QOpenGLFunctions;
@@ -103,6 +109,8 @@ public:
     QOpenGLContextGroup *shareGroup() const;
     QScreen *screen() const;
 
+    GLuint defaultFramebufferObject() const;
+
     bool makeCurrent(QSurface *surface);
     void doneCurrent();
 

src/gui/kernel/qopenglcontext_p.h

@@ -47,6 +47,10 @@
 #include <private/qobject_p.h>
 #include <qmutex.h>
 
+#ifndef QT_NO_DEBUG
+#include <QtCore/QHash>
+#endif
+
 QT_BEGIN_HEADER
 
 QT_BEGIN_NAMESPACE
@@ -185,7 +189,6 @@ public:
         , surface(0)
         , functions(0)
         , current_fbo(0)
-        , default_fbo(0)
         , workaround_brokenFBOReadBack(false)
         , workaround_brokenTexSubImage(false)
         , active_engine(0)
@@ -210,7 +213,6 @@ public:
     QOpenGLFunctions *functions;
 
     GLuint current_fbo;
-    GLuint default_fbo;
 
     bool workaround_brokenFBOReadBack;
     bool workaround_brokenTexSubImage;
@@ -220,6 +222,23 @@ public:
     static void setCurrentContext(QOpenGLContext *context);
 
     int maxTextureSize() const { return 1024; }
+
+#if !defined(QT_NO_DEBUG)
+    static bool toggleMakeCurrentTracker(QOpenGLContext *context, bool value)
+    {
+        QMutexLocker locker(&makeCurrentTrackerMutex);
+        bool old = makeCurrentTracker.value(context, false);
+        makeCurrentTracker.insert(context, value);
+        return old;
+    }
+    static void cleanMakeCurrentTracker(QOpenGLContext *context)
+    {
+        QMutexLocker locker(&makeCurrentTrackerMutex);
+        makeCurrentTracker.remove(context);
+    }
+    static QHash<QOpenGLContext *, bool> makeCurrentTracker;
+    static QMutex makeCurrentTrackerMutex;
+#endif
 };
 
 QT_END_NAMESPACE

src/gui/kernel/qplatformopenglcontext_qpa.cpp

@@ -41,6 +41,8 @@
 
 #include "qplatformopenglcontext_qpa.h"
 
+#include <QOpenGLFunctions>
+
 QT_BEGIN_NAMESPACE
 
 /*!
@@ -94,6 +96,16 @@ QPlatformOpenGLContext::~QPlatformOpenGLContext()
 {
 }
 
+/*!
+    Reimplement in subclass if your platform uses framebuffer objects for surfaces.
+
+    The default implementation returns 0.
+*/
+GLuint QPlatformOpenGLContext::defaultFramebufferObject(QPlatformSurface *) const
+{
+    return 0;
+}
+
 QOpenGLContext *QPlatformOpenGLContext::context() const
 {
     Q_D(const QPlatformOpenGLContext);

src/gui/kernel/qplatformopenglcontext_qpa.h

@@ -45,6 +45,7 @@
 #include <QtCore/qnamespace.h>
 #include <QtGui/qsurfaceformat.h>
 #include <QtGui/qwindow.h>
+#include <QtGui/qopengl.h>
 
 QT_BEGIN_HEADER
 
@@ -64,6 +65,8 @@ public:
 
     virtual void swapBuffers(QPlatformSurface *surface) = 0;
 
+    virtual GLuint defaultFramebufferObject(QPlatformSurface *surface) const;
+
     virtual bool makeCurrent(QPlatformSurface *surface) = 0;
     virtual void doneCurrent() = 0;
 

src/gui/opengl/qopenglframebufferobject.cpp

@@ -892,8 +892,8 @@ bool QOpenGLFramebufferObject::release()
 #endif
 
     if (current) {
-        current->d_func()->current_fbo = current->d_func()->default_fbo;
+        current->d_func()->current_fbo = current->defaultFramebufferObject();
-        d->funcs.glBindFramebuffer(GL_FRAMEBUFFER, current->d_func()->default_fbo);
+        d->funcs.glBindFramebuffer(GL_FRAMEBUFFER, current->d_func()->current_fbo);
     }
 
     return true;
@@ -1057,8 +1057,8 @@ bool QOpenGLFramebufferObject::bindDefault()
     QOpenGLFunctions functions(ctx);
 
     if (ctx) {
-        ctx->d_func()->current_fbo = ctx->d_func()->default_fbo;
+        ctx->d_func()->current_fbo = ctx->defaultFramebufferObject();
-        functions.glBindFramebuffer(GL_FRAMEBUFFER, ctx->d_func()->default_fbo);
+        functions.glBindFramebuffer(GL_FRAMEBUFFER, ctx->d_func()->current_fbo);
 #ifdef QT_DEBUG
     } else {
         qWarning("QOpenGLFramebufferObject::bindDefault() called without current context.");

src/gui/opengl/qopenglfunctions.cpp

@@ -478,6 +478,9 @@ void QOpenGLFunctions::initializeGLFunctions()
 
     Convenience function that calls glBindFramebuffer(\a target, \a framebuffer).
 
+    Note that Qt will translate a \a framebuffer argument of 0 to the currently
+    bound QOpenGLContext's defaultFramebufferObject().
+
     For more information, see the OpenGL/ES 2.0 documentation for
     \l{http://www.khronos.org/opengles/sdk/docs/man/glBindFramebuffer.xml}{glBindFramebuffer()}.
 */

src/gui/opengl/qopenglfunctions.h

@@ -478,6 +478,8 @@ inline void QOpenGLFunctions::glBindBuffer(GLenum target, GLuint buffer)
 
 inline void QOpenGLFunctions::glBindFramebuffer(GLenum target, GLuint framebuffer)
 {
+    if (framebuffer == 0)
+        framebuffer = QOpenGLContext::currentContext()->defaultFramebufferObject();
 #if defined(QT_OPENGL_ES_2)
     ::glBindFramebuffer(target, framebuffer);
 #else

src/opengl/qglfunctions.cpp

@@ -395,6 +395,9 @@ void QGLFunctions::initializeGLFunctions(const QGLContext *context)
 
     Convenience function that calls glBindFramebuffer(\a target, \a framebuffer).
 
+    Note that Qt will translate a \a framebuffer argument of 0 to the currently
+    bound QOpenGLContext's defaultFramebufferObject().
+
     For more information, see the OpenGL/ES 2.0 documentation for
     \l{http://www.khronos.org/opengles/sdk/docs/man/glBindFramebuffer.xml}{glBindFramebuffer()}.
 */

src/opengl/qglfunctions.h

@@ -48,6 +48,7 @@
 #endif
 
 #include <QtOpenGL/qgl.h>
+#include <QtGui/qopenglcontext.h>
 
 QT_BEGIN_HEADER
 
@@ -450,6 +451,8 @@ inline void QGLFunctions::glBindBuffer(GLenum target, GLuint buffer)
 
 inline void QGLFunctions::glBindFramebuffer(GLenum target, GLuint framebuffer)
 {
+    if (framebuffer == 0)
+        framebuffer = QOpenGLContext::currentContext()->defaultFramebufferObject();
 #if defined(QT_OPENGL_ES_2)
     ::glBindFramebuffer(target, framebuffer);
 #else