Add protected virtual ensureActiveTarget() to QOpenGLPaintDevice

Make sure that QOpenGLPaintDevice supports it the same way as
QGLPaintDevice::ensureActiveTarget dit. It is made virtual since the
external code needs to manage FBOs for QOpenGLPaintEngine.

Task-number: QTBUG-25995
Change-Id: Ieed9616f6a14204aae628d7febe6a11538496b3d
Reviewed-by: Kim M. Kalland <kim.kalland@nokia.com>

3 files changed, 15 insertions, 0 deletions

diff --git a/src/gui/opengl/qopenglpaintdevice.cpp b/src/gui/opengl/qopenglpaintdevice.cpp
index 60f5e3192a..e070ee6c58 100644
--- a/src/gui/opengl/qopenglpaintdevice.cpp
+++ b/src/gui/opengl/qopenglpaintdevice.cpp
@@ -244,4 +244,15 @@ bool QOpenGLPaintDevice::paintFlipped() const
     return d_ptr->flipped;
 }
 
+/*!
+    This virtual method is provided as a callback to allow re-binding a
+    target frame buffer object when different QOpenGLPaintDevice instances
+    are issuing draw calls alternately on the same OpenGL context.
+
+    QPainter::beginNativePainting will also trigger this method.
+*/
+void QOpenGLPaintDevice::ensureActiveTarget()
+{
+}
+
 QT_END_NAMESPACE
diff --git a/src/gui/opengl/qopenglpaintdevice.h b/src/gui/opengl/qopenglpaintdevice.h
index a07d11062f..44acbab031 100644
--- a/src/gui/opengl/qopenglpaintdevice.h
+++ b/src/gui/opengl/qopenglpaintdevice.h
@@ -80,6 +80,8 @@ public:
     void setPaintFlipped(bool flipped);
     bool paintFlipped() const;
 
+    virtual void ensureActiveTarget();
+
 protected:
     int metric(QPaintDevice::PaintDeviceMetric metric) const;
 
diff --git a/src/gui/opengl/qopenglpaintengine.cpp b/src/gui/opengl/qopenglpaintengine.cpp
index 2f84a0f295..bbe5854031 100644
--- a/src/gui/opengl/qopenglpaintengine.cpp
+++ b/src/gui/opengl/qopenglpaintengine.cpp
@@ -2013,6 +2013,8 @@ void QOpenGL2PaintEngineEx::ensureActive()
     }
 
     if (d->needsSync) {
+        d->device->ensureActiveTarget();
+
         d->transferMode(BrushDrawingMode);
         glViewport(0, 0, d->width, d->height);
         d->needsSync = false;