QGraphicsView with QGLWidget viewport renders child widgets incorrectly on Mac

Rodskjegg

Hi,

as the title suggests I am having child widgets of a QGraphicsView rendered incorrectly on Mac if its viewport is a QGLWidget. Additionally multiple error messages are dumped to the console:

Jul 24 15:54:51 Martin-Havnrs-MacBook-Pro.local OSMViewerQt[4467] <Error>: CGContextSetShouldAntialias: invalid context 0x0
Jul 24 15:54:51 Martin-Havnrs-MacBook-Pro.local OSMViewerQt[4467] <Error>: CGContextSetShouldSmoothFonts: invalid context 0x0
Jul 24 15:54:51 Martin-Havnrs-MacBook-Pro.local OSMViewerQt[4467] <Error>: CGContextSetFillColorSpace: invalid context 0x0
Jul 24 15:54:51 Martin-Havnrs-MacBook-Pro.local OSMViewerQt[4467] <Error>: CGContextSetFillColor: invalid context 0x0
QMacCGContext:: Unsupported painter devtype type 1
QMacCGContext:: Unsupported painter devtype type 1
QMacCGContext:: Unsupported painter devtype type 1

Testing the code on Windows and Linux does not cause the error messages, but there are slight deviations in how child widgets are rendered.

Here's the strange part: setting the window opacity of the child widget to anything but its default value 1.0 fixes the problem. Ie.uncomment the setWindowOpacity(0.99); line and the bug is gone. However this seriously impairs performance on more advanced scenes than the one described below.

Code that reproduces the problem:
@

#include <QApplication>

#include <QtWidgets>
#include <QGLFormat>

int main(int argc, char *argv[]) {
QApplication app(argc, argv);

// Create a graphics scene
QGraphicsScene scene;

// Create a graphics view for the scene
QGraphicsView view(&scene);

// Define a GLWidget viewport for the graphics view
view.setViewport(new QGLWidget());

// Create an overlay with a layout containing more widgets
QGroupBox *groupBox = new QGroupBox("Contact Details");
QFormLayout *layout = new QFormLayout;
layout->addRow(new QLabel("Telephone number"), new QLineEdit());
groupBox->setLayout(layout);

// Add the overlay to the graphics scene
QGraphicsProxyWidget *proxy = scene.addWidget(groupBox);

// By setting the overlay as semi-transparent the app works. It severely slows down an application with performance requirements.
// Why is this needed? Can it be avoided?
// groupBox->setWindowOpacity(0.99);

// Give the graphics view a size and show it
view.resize(400, 400);
view.show();

return app.exec();

}
@

The code is taken from the "Qt 5.0 documentation":http://qt-project.org/doc/qt-5.0/qtwidgets/qgraphicsproxywidget.html - simply changing its QGraphicsView viewport to a QGLWidget.

The example main() from above was run in a larger project with the following modules added to the .pro file should that have any effect:
QT += opengl
QT += network
QT += sql
QT += webkitwidgets
QT += svg

Why do I see deviations in how widgets are rendered with the QGLWidget viewport?
Where does the nil-context attempted used somewhere in rendering come from?
Why does adding window opacity seemingly fix the issue?
What can I do to avoid these problems without the window opacity hack?

Br.
Martin Havnør

SGaist

Hi and welcome to devnet,

Sounds like a bug to me, did you try to look at the "bug report system":https://bugreports.qt-project.org/issues/ to see if someone already reported this ?

If not you might consider open a bug report with all the information you provided in this post.

Maybe asking on the interest mailing list (this is where you'll find Qt's developer/maintainer, this forum is more user oriented)

Rodskjegg

I will give that a try, thanks for the good suggestion.

Br.
Martin Havnør