From cc27a50ef8d7de08df48ea25e89e6f1fb9f0dc2e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tor=20Arne=20Vestb=C3=B8?= <tor.arne.vestbo@qt.io>
Date: Wed, 18 Jul 2018 20:36:26 +0200
Subject: [PATCH] QGLWidget: Gracefully handle failed makeCurrent during resize
 and paint event
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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 <simon.hausmann@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
---
 src/opengl/qgl.cpp | 17 +++++++++++++----
 src/opengl/qgl_p.h |  2 ++
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/opengl/qgl.cpp b/src/opengl/qgl.cpp
index 4eb7a194d9..1132411d42 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 6b4d83888f..ed364283cc 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;