Fastest way to paint a lot of squares



  • Hello,
    in my current project I have to draw a lot of squares (amount can vary between 100 and 2^27 (~10^8), which build a grid. Each square has a specific color (7 different colors) which is updated really fast and often (ca. 500Hz).
    Now I am searching for the most performant way to realise this.
    In an older version I used QGraphicsView and QGraphicsScene with a subclass of QGraphicsItem for each square, but the result was too slow and it looked not very smoothy.
    I know that the human can't really recognize 500 frames per second, but the update rate is that high and I simply want to display a smoothy picture which shows any greater change.
    What is currently the best Widget I have to choose? An OpenGL-Widget? With QGraphicsView or not? A lot of independent Widgets? I read of a new QQuickWindow. Is it possible to use this widget for my purpose?

    If you have any further questions or I wrote anything unintelligible, don't hesitate to ask.

    Thank you!


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    If you want fast graphics then go with OpenGL.

    However realise that beside the fact that the human eye/brain can't handle 500Hz refresh rate, there's currently no consumer device that does this either. Even current high-end graphics card don't provide such a refresh rate and no screens supports that.



  • Thanks for your answer and your advice. I will try out OpenGL.

    I know that 500Hz are too high for human senses, but I just wanted to mention the actual refresh rate of the state. You can't either see the single squares if there are 2^27 of them. I only want to see the approximate movement of square groups. So you don't actually need 500Hz, 50-60Hz would be more than enough (my monitor actually can''t display more FPS). But with my current implementation I have a refresh rate of ~2-3Hz. But yeah, you are right. I think I simply have to skip some states and draw only every tenth color of a square. That might be the weakness in my current version.


  • Lifetime Qt Champion

    It's a bit like video games: only draw precisely what a user can see closely and then start reducing the quality for what is behind until you can even drop what's far.


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