Qml Image : bad performance opengl backend



  • Hi,

    I have a lot of images in qml desktop fullscreen application (opengl viewport) on Windows Seven... When one image is quite large, for example 4000x4000 pixels, the framerate drops, ... when I have a lots of not very big image .. I have the same issue : I use for years opengl and I am sure that I can do the same in pure opengl with a computer 5 years old ... So i don't understand why I don't have decent performance : I use for now QT4.7.4, I suppose I can try 4.8 but I have find this report : https://bugreports.qt-project.org/browse/QTBUG-23253

    Has anyone tryed to reimplement a custom qml image using qdeclarativeitem and opengl ?



  • Hello, I am working on a project in which I will have to dig deeper into images management performed in QML/Qt. i will try to develop an advance image caching mechanism. I may come accross several difficulties close to the one you are having now. I will try to keep you updated if I come accross any hints for you.
    Bill



  • I think you will find that 4kx4k textures aren't supported on all modern hardware. Therefore, you will struggle to do such large images on 5yr old hardware.

    Are you on Intel graphics hardware?

    Furthermore, some drivers will automatically tile your image; so you need to be careful of what you are really doing to the graphics hardware.

    I would suggest that you:

    Try your code on a modern NVidia setup. That should do 4k textures.

    Try to limit the amount of texture bandwidth you are consuming.

    Run your application under GDebugger and start attempting to understand where the performance bottlenecks are in your software.

    Consider using native opengl and a QGLWidget. Then it is up to you to ensure you're getting the correct performance.

    Good luck,

    -bms



  • I am not using intel graphics card : I have tested and performance are horrible with small images ! I hopes that with Qt5 it will works better...
    I am using for example gtx560 nvidia card ...


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