Performance trouble in Graphics View

[zgulser]

Hi again,

I'm about to finish my project but I'm currently suffering from the performance. My cursor barely moves(very slow) on the scene. I want you to let me know what possible problem that I'm facing now. Any little idea can be significantly change the performance so please share.

I have number of graphics item inside other graphics item which are all inside the scene and view as usual. I mostly reimplemented boundingRect() and shape() methods together to increase performance when necessary.

If you can't figure out what's I'm saying above, please let me know again.

Cheers, Zeck.

[wysota]

Please provide more information - what optimizations you already enabled, what items are we talking about, what are their shapes, how many of them are there, etc.

[zgulser]

Sure,

think you have a graphicsitems which resides in a graphics item group. they are all in scene and view.

Now, I reimplement shape() in addition to boundingRect() in order to optimize mouse operations. I already reimplemented boundingRect() in the item group, scene and view as well as i'm supposed to do.

My graphics item are movable. I did drag-drop issue by using itemChange(). I mean when position changes by the mouse, itemChange() method deals with the necessary things( i.e. changing core data) in itself. I suspect there should be something like recursion between itemChange() and paint(). I'm now looking for it.

By the way shapes are polygons that excellently covers around items.

[wysota]

What's the exact implementation of boundingRect() and shape()? Do you cache items? What's the bottle-neck according to the profiler?

[zgulser]

I'm not allowed to provide code. Sorry for this first of all.

As I said before, in shape() I return a polygon which exactly covers around my item. In boundingRect() I just return a QRect with arbitrary sizes like;

return new QRect(-1000, -1000, 2000, 2000);

return new QRect(-1000, -1000, 2000, 2000);

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[wysota]

Cache as much data as possible. Find the bottleneck using a profiler and eliminate it.

[zgulser]

Hi,

Can you explain a bit more about caching if you don't mind ?.

[wysota]

Cache the data - don't create instances of QRectF and QPainterPath on every call to boundingRect() and shape(). Also cache the items. And please use a profiler instead of just guessing.

[scascio]

Have you tried to use OpenGL as the viewport of your QGraphicsView?
It may increase performance.

It is so easy as :

setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

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