Need suggestion how to generate current scene image in performance sensitive app

nlazovic 0

I am working on app that is doing offscreen rendering (QOffscreenSurface / QOpenGLFramebufferObject).
Once per every frame I have to get scene image (and process it)

My current approach is to (on main thread) take image from QOpenGLFramebufferObject and process it. See below.
Unfortunatelly QOpenGLFramebufferObject::toImage() executes very very slow, causing that my app can not render more then 5-8 fps.
Without call to QOpenGLFramebufferObject::toImage(), I am getting easily 30fps+.

When i make fbo copy (QOpenGLFramebufferObject::blitFramebuffer(workerFbo, m_fbo)) and pass workerFbo to worker thread to do toImage() on it, I am getting

QOpenGLFramebufferObject::toImage() called without a current context

Is there any other (faster) approach to get current scene image ?
How to copy / set context on worker thread, so that I can do QOpenGLFramebufferObject::toImage() on worker thread ?

Current approach

MySceneRenderer::renderNext() {
    ... on main thread
    //get image from current QOpenGLFramebufferObject m_fbo
    QImage fboImage(m_fbo->toImage());
    //process image
    sceneProcessor.process(fboImage);
   ...
}

SGaist

Hi,

Out of curiosity, what processing do you need to apply ?

nlazovic 0

@SGaist
... take portion of overall scene, and stream to remote clients.
Planning to use GStreamer/gst-rtsp-server to stream out. Running on separate thread.
So far bottleneck is converting framebuffer to image ...

SGaist

Then you should check the QtGStreamer module. It might make things easier.