Fix crash when combining QOpenGLWidget, QStaticText and Qt Quick

Under certain circumstances, if you had a widget with a QOpenGLPaintEngine,
and drew QStaticText into this, and then later had Qt Quick access the same
cache and try to resize it, we would get a crash because the resize function
would have a pointer to the paint engine and try to access its shader manager
(which would now be null, since this is outside the begin()/end() phase of the
paint engine.

The solution is to reset the paint engine pointer to null on the cache once it
has been populated and it is no longer needed.

[ChangeLog][QtGui][Text] Fixed a possible crash when combining QStaticText,
QOpenGLWidget and Qt Quick in the same application.

Task-number: QTBUG-70096
Change-Id: I7383ad7456d1a72499cfcd2da09a5a808d4b3eff
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 6 insertions, 0 deletions

diff --git a/src/gui/opengl/qopenglpaintengine.cpp b/src/gui/opengl/qopenglpaintengine.cpp
index 3d1c362275..6a89089f18 100644
--- a/src/gui/opengl/qopenglpaintengine.cpp
+++ b/src/gui/opengl/qopenglpaintengine.cpp
@@ -1741,6 +1741,7 @@ void QOpenGL2PaintEngineExPrivate::drawCachedGlyphs(QFontEngine::GlyphFormat gly
             // we may have to re-bind brush textures after filling in the cache.
             brushTextureDirty = (QT_BRUSH_TEXTURE_UNIT == glypchCacheTextureUnit);
         }
+        cache->setPaintEnginePrivate(nullptr);
     }
 
     if (cache->width() == 0 || cache->height() == 0)
diff --git a/src/gui/opengl/qopengltextureglyphcache_p.h b/src/gui/opengl/qopengltextureglyphcache_p.h
index 0b7b5f6082..598cb00ee5 100644
--- a/src/gui/opengl/qopengltextureglyphcache_p.h
+++ b/src/gui/opengl/qopengltextureglyphcache_p.h
@@ -152,6 +152,11 @@ public:
 
     void clear();
 
+    QOpenGL2PaintEngineExPrivate *paintEnginePrivate() const
+    {
+        return pex;
+    }
+
 private:
     void setupVertexAttribs();