[Interest] OpenGL cpu benchmark QtQuick vs OSX Native

[Bruno Di Giorgi]

Dear mailing list,

First time I write here, I posted this yesterday on the QtQuick forum and a user recommended me to post on this mailing list.

I noticed some heavy cpu usage in a QtQuick (using Qt5.5) osx app compared to an equivalent Native OSX app. Around 5% more cpu usage with a simple app, up to 15% more with more complex OpenGL tasks.

Both are using Core profile
Version: 4.1 INTEL-10.6.33
GLSL: 4.10

In QtQuick I do openGL inside a QQuickFramebufferObject as I've seen advised many times.
In OSX I draw inside a subclass of NSOpenGLView.

Here are the OpenGL Profiler statistics: http://pastebin.com/uWyy8RMk <http://pastebin.com/uWyy8RMk> 
Where you can see that CGLFlushDrawable takes so much longer in QtQuick (avg 15418.39 microsec) than in Native OSX App (avg 1287.65 microsec).

I know that what CGLFlushDrawable really does is to set the internal OpenGL state and then do the drawing, so I wonder if I am misusing QtQuick OpenGL somehow. Here is how I set up OpenGL in QtQuick app:

	QSurfaceFormat f;
	f.setVersion(4, 1);
	f.setProfile(QSurfaceFormat::CoreProfile);
	QSurfaceFormat::setDefaultFormat(f);

Then, when setting the framebuffer (inside QQuickFramebufferObject::Renderer method createFramebufferObject):

	QOpenGLFramebufferObjectFormat format;
	format.setAttachment(QOpenGLFramebufferObject::Depth);
	format.setInternalTextureFormat(GL_RGB);
	format.setSamples(0);

I really hope there is a solution that makes me achieve similar performance because I really enjoy QML and I'd like to continue using it.

Hardware used:
MacBookPro 13'' with retina screen,
cpu: 3 GHz Intel Core i7
gpu: Intel Iris 1536 MB

Best,
Bruno Di Giorgi

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