QGLWidget: Gracefully handle failed makeCurrent during resize and paint event

The underlying QOpenGLContext may fail to be made current, e.g. if the
surface is not exposed, or the graphics hardware is not available.

Instead of trying to initialize and resize the GL viewport with a
non-current context, we return early and defer the init and resize
until later.

Change-Id: I278ca8f1ad4d3da2d5be18b44d775f8d6c8af726
Reviewed-by: Simon Hausmann <[email protected]>
Reviewed-by: Tor Arne Vestbø <[email protected]>

2 files changed, 15 insertions, 4 deletions

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 4eb7a194d91..1132411d420 100644
--- a/src/opengl/qgl.cpp
+++ b/src/opengl/qgl.cpp
@@ -4084,7 +4084,13 @@ bool QGLWidget::isSharing() const
 void QGLWidget::makeCurrent()
 {
     Q_D(QGLWidget);
-    d->glcx->makeCurrent();
+    d->makeCurrent();
+}
+
+bool QGLWidgetPrivate::makeCurrent()
+{
+    glcx->makeCurrent();
+    return QGLContext::currentContext() == glcx;
 }
 
 /*!
@@ -4422,7 +4428,8 @@ void QGLWidget::resizeEvent(QResizeEvent *e)
     QWidget::resizeEvent(e);
     if (!isValid())
         return;
-    makeCurrent();
+    if (!d->makeCurrent())
+        return;
     if (!d->glcx->initialized())
         glInit();
     const qreal scaleFactor = (window() && window()->windowHandle()) ?
@@ -4537,7 +4544,8 @@ void QGLWidget::glInit()
     Q_D(QGLWidget);
     if (!isValid())
         return;
-    makeCurrent();
+    if (!d->makeCurrent())
+        return;
     initializeGL();
     d->glcx->setInitialized(true);
 }
@@ -4555,7 +4563,8 @@ void QGLWidget::glDraw()
     Q_D(QGLWidget);
     if (!isValid())
         return;
-    makeCurrent();
+    if (!d->makeCurrent())
+        return;
 #ifndef QT_OPENGL_ES
     if (d->glcx->deviceIsPixmap() && !d->glcx->contextHandle()->isOpenGLES())
         qgl1_functions()->glDrawBuffer(GL_FRONT);
diff --git a/src/opengl/qgl_p.h b/src/opengl/qgl_p.h
index 6b4d83888fe..ed364283ccd 100644
--- a/src/opengl/qgl_p.h
+++ b/src/opengl/qgl_p.h
@@ -145,6 +145,8 @@ public:
             glcx->reset();
     }
 
+    bool makeCurrent();
+
     QGLContext *glcx;
     QGLWidgetGLPaintDevice glDevice;
     bool autoSwap;