3 files changed, 24 insertions, 4 deletions
diff --git a/src/opengl/qglfunctions.h b/src/opengl/qglfunctions.h
index e06de7f..88f43c0 100644
--- a/src/opengl/qglfunctions.h
+++ b/src/opengl/qglfunctions.h
@@ -42,6 +42,11 @@
 #ifndef QGLFUNCTIONS_H
 #define QGLFUNCTIONS_H
 
+#ifdef __GLEW_H__
+#warning qglfunctions.h is not compatible with GLEW, GLEW defines will be undefined
+#warning To use GLEW with Qt, do not include <QtOpenGL> or <QGLFunctions> after glew.h
+#endif
+
 #include <QtOpenGL/qgl.h>
 
 QT_BEGIN_HEADER
diff --git a/src/opengl/qwindowsurface_gl.cpp b/src/opengl/qwindowsurface_gl.cpp
index 6185ff8..81575e3 100644
--- a/src/opengl/qwindowsurface_gl.cpp
+++ b/src/opengl/qwindowsurface_gl.cpp
@@ -302,6 +302,7 @@ struct QGLWindowSurfacePrivate
 };
 
 QGLFormat QGLWindowSurface::surfaceFormat;
+QGLWindowSurface::SwapMode QGLWindowSurface::swapBehavior = QGLWindowSurface::AutomaticSwap;
 
 void QGLWindowSurfaceGLPaintDevice::endPaint()
 {
@@ -549,9 +550,10 @@ void QGLWindowSurface::flush(QWidget *widget, const QRegion &rgn, const QPoint &
 
     // did_paint is set to true in ::beginPaint. ::beginPaint means that we
     // at least cleared the background (= painted something). In EGL API it's a
-    // mistakte to call swapBuffers if nothing was painted. This check protects
-    // the flush func from being executed if it's for nothing.
-    if (!d_ptr->did_paint)
+    // mistake to call swapBuffers if nothing was painted unless
+    // EGL_BUFFER_PRESERVED is set. This check protects the flush func from
+    // being executed if it's for nothing.
+    if (!hasPartialUpdateSupport() && !d_ptr->did_paint)
         return;
 
     QWidget *parent = widget->internalWinId() ? widget : widget->nativeParentWidget();
@@ -576,6 +578,9 @@ void QGLWindowSurface::flush(QWidget *widget, const QRegion &rgn, const QPoint &
     const GLenum target = GL_TEXTURE_2D;
     Q_UNUSED(target);
 
+    if (QGLWindowSurface::swapBehavior == QGLWindowSurface::KillSwap)
+        return;
+
     if (context()) {
         context()->makeCurrent();
 
@@ -623,7 +628,14 @@ void QGLWindowSurface::flush(QWidget *widget, const QRegion &rgn, const QPoint &
                 }
             }
 #endif
-            bool doingPartialUpdate = hasPartialUpdateSupport() && br.width() * br.height() < parent->geometry().width() * parent->geometry().height() * 0.2;
+            bool doingPartialUpdate = false;
+            if (QGLWindowSurface::swapBehavior == QGLWindowSurface::AutomaticSwap)
+                doingPartialUpdate = hasPartialUpdateSupport() && br.width() * br.height() < parent->geometry().width() * parent->geometry().height() * 0.2;
+            else if (QGLWindowSurface::swapBehavior == QGLWindowSurface::AlwaysFullSwap)
+                doingPartialUpdate = false;
+            else if (QGLWindowSurface::swapBehavior == QGLWindowSurface::AlwaysPartialSwap)
+                doingPartialUpdate = hasPartialUpdateSupport();
+
             QGLContext *ctx = reinterpret_cast<QGLContext *>(parent->d_func()->extraData()->glContext);
             if (widget != window()) {
                 if (initializeOffscreenTexture(window()->size()))
diff --git a/src/opengl/qwindowsurface_gl_p.h b/src/opengl/qwindowsurface_gl_p.h
index 22bd5f0..09a6a30 100644
--- a/src/opengl/qwindowsurface_gl_p.h
+++ b/src/opengl/qwindowsurface_gl_p.h
@@ -112,6 +112,9 @@ public:
 
     static QGLFormat surfaceFormat;
 
+    enum SwapMode { AutomaticSwap, AlwaysFullSwap, AlwaysPartialSwap, KillSwap };
+    static SwapMode swapBehavior;
+
 private slots:
     void deleted(QObject *object);