[Interest] QML Profiler questions

VStevenP vstevenpavao at yahoo.com
Wed Oct 30 20:52:07 CET 2013

I have 2 QML Profiler questions.  I am profiling a simple Knob widget which is made out of an Image and a MouseArea, with some Javscript to control the rotation property of the Image.

When I profile the Knob in QML Profiler, I see that the Knob is efficient, in that there are no Paint events.   This must mean that when the Knob is created, the Knob png is sent to the GPU, and after that, the rotation is simply controlled by a rotation command sent to the GPU for that Image.  Hopefully, I understand that correctly.

Question 1:  Is the rotation command that is sent to the GPU considered to be a 'compositing event', and if so, will QML Profiler show compositing activity separately, as in Chrome Dev Tools in Chrome?

I also discovered that in Qt 5.1, if you manipulate opacity on an Item during onPressed and onReleased mouse events, Paint events occur for that Item even when the Item has visible: false.  I would think that visible property would supersede opacity to ensure most efficient draw.

Question 2: Should I report this as a bug?

I was going to try and test these on Qt 5.2 Beta, because I know the scene graph renderer has been reworked, but I'm not able to run the QML Profiler in Qt 5.2 Beta like I can in Qt Creator 2.7.2/Qt 5.1.  I entered a bug about that already.

- VStevenP

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