QGraphicsScene/QGraphicsView performance problems

[wysota]

I made my own experiments. With about 0.5M items the application was using about 80 megabytes of memory which gives an average of 160 bytes per item (including the memory used by all other components) which I think is not that bad. At that point the application was responsive although very slow. The slowdown is caused by the fact that even if I intend not to draw some item, the matrix still has to be produced and applied for each of them. Making the architecture ignore items that are sure not to be drawn would speed the app significantly.

See attached the code I used.

[bnilsson]

I made my own experiments. With about 0.5M items the application was using about 80 megabytes of memory which gives an average of 160 bytes per item (including the memory used by all other components) which I think is not that bad. At that point the application was responsive although very slow. The slowdown is caused by the fact that even if I intend not to draw some item, the matrix still has to be produced and applied for each of them. Making the architecture ignore items that are sure not to be drawn would speed the app significantly.

Will this be someting for a future Qt release?

See attached the code I used.

I will study the code, I will probably learn a lot from it. Thanks!

[wysota]

Will this be someting for a future Qt release?

I don't think Andreas' team has such plans You'd have to implement it yourself by reimplementing drawItems() in the scene (I think).

[Gopala Krishna]

Making the architecture ignore items that are sure not to be drawn would speed the app significantly.

Is it true ? or did i misunderstand ?
I was under impression that GV framework doesn't draw items not visible on viewport (ofcourse i dont mean hidden items)

[wysota]

I was under impression that GV framework doesn't draw items not visible on viewport (ofcourse i dont mean hidden items)

Take a look at my code. I'm deciding whether to draw something or not based on the distance between the object and the camera (level of detail). If something is very far away (but still inside the camera's viewport) I decide not to draw it, but the whole painting environment is set up by the architecture anyway.