Elvis, Using your quick example (attached as a project below) I’ve run some tests and realised that window rendering it not happening at the same frame rate in all machines and the maximum differs:
- no more than 30 fps in on a 2017 iMac with Radeon graphics card - no more than 30 fps on 2019 Intel Mac Book with Intel Graphics - up to 144 fps on a Windows machine with an RTX 2060 - 115 fps on a 2018 12.9” iPad Pro Changing the width and height of the scene doesn’t seem to impact the frame rate. I was expecting to have more than 60 fps on the iMac and Macbook. I don’t think this simple scene would be limited to 30 fps At this point, I’m not taking into consideration that time it takes to obtain the pixel data from the fbo/texture. Since in order to have v-sync with window when painting the context of the texture rendered on the offscreen renderer I need to drive the paint via main window paint, this means that I will be limited by main window painting frame rate. Is anyone aware of frame rate limitations of a qquickwindow painting? Project attached. Thanks, Best regards, Nuno
<<attachment: test-quick-grab.zip>>
> On 14 Jul 2021, at 23:48, Elvis Stansvik <elvst...@gmail.com> wrote:
>
> My idea would be something like (sketch):
>
> main.cpp:
>
> #include <QGuiApplication>
> #include <QQuickView>
> #include <QObject>
> #include <QMutex>
> #include <QVector>
>
> int main(int argc, char *argv[])
> {
> QGuiApplication app(argc, argv);
>
> auto view = new QQuickView;
> view->setSource(QUrl::fromLocalFile("test.qml"));
> view->show();
>
> // I use a QVector here, but you would have your AVFrame and
> // its allocated memory buffer..
> QVector<unsigned char> buffer;
> QMutex mutex;
>
> QObject::connect(view, &QQuickView::afterRendering, view, [&]() {
> mutex.lock();
> buffer.resize(4 * view->width() * view->height());
> glReadPixels(0, 0, view->width(), view->height(), GL_RGBA,
> GL_UNSIGNED_BYTE, buffer.data());
> mutex.unlock();
> }, Qt::DirectConnection);
>
> return app.exec();
> }
>
> test.qml:
>
> import QtQuick 2.2
>
> Rectangle {
> width: 1920
> height: 1080
>
> Rectangle {
> width: 500
> height: 500
> color: "green"
> anchors.centerIn: parent
> RotationAnimation on rotation {
> from: 0
> to: 360
> duration: 2000
> loops: Animation.Infinite
> }
> }
> }
>
> I don't know whether this would work for you.
>
> Elvis
>
> Den tis 13 juli 2021 kl 15:31 skrev Nuno Santos <nuno.san...@imaginando.pt>:
>>
>> Elvis,
>>
>> Thanks for sharing your thoughts. It makes sense.
>>
>> I need to dive into the toImage function, try to read directly the bytes
>> from the FBO and see if that has any performance impact.
>>
>> Best regards,
>>
>> Nuno
>>
>>> On 13 Jul 2021, at 14:10, Elvis Stansvik <elvst...@gmail.com> wrote:
>>>
>>> Hi Nuno,
>>>
>>> I'm really out of my waters here, but, provided you don't need to hold
>>> on to each AVFrame after you are "done with it", you could perhaps
>>> avoid having to allocate a QImage for each frame (which toImage forces
>>> you to do) by just allocating a a single AVFrame and a single memory
>>> buffer for it, and then do what toImage does, which is make sure the
>>> FBO is bound and read the pixels off of it with glReadPixels. Then you
>>> could read the pixels straight into the memory buffer used by your
>>> AVFrame.
>>>
>>> That way you would save the overhead of a new QImage being allocated
>>> each time, which might speed things up..?
>>>
>>> Just ideas here. Have not worked with GL or ffmpeg before.
>>>
>>> Elvis
>>>
>>> Den tis 13 juli 2021 kl 11:22 skrev Nuno Santos <nuno.san...@imaginando.pt>:
>>>>
>>>> Hi,
>>>>
>>>> I’m trying to capture the content of an FBO to a video file. This video
>>>> file should contain the animations generated by a qml scene.
>>>>
>>>> To do this, I’m recurring to QOpenGLFramebufferObject class toImage()
>>>> method.
>>>>
>>>> My scene is being drawn at 1920x1080. Each call to toImage takes 30 ms! :(
>>>>
>>>> If I want to render to file at 60 fps, ideally, this call would need to
>>>> take less than 16 ms to give me room to do other operations, such as video
>>>> encoding and the actual render.
>>>>
>>>> As anyone been here before? What other strategies are available to copy
>>>> the FBO data to an image?
>>>>
>>>> I’m using libav to encode the video file, therefor I need to fill an
>>>> AVFrame. Right now I’m filling the AVFrame from the QImage generated by
>>>> the FBO toImage method.
>>>>
>>>> Does any one knows a method of filling an AVFrame directly from texture
>>>> data?
>>>>
>>>> Thanks
>>>>
>>>> Best regards,
>>>>
>>>> Nuno
>>>> _______________________________________________
>>>> Interest mailing list
>>>> Interest@qt-project.org
>>>> https://lists.qt-project.org/listinfo/interest
>>
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