CPU usage is too high with update()

URPradhan

Hi Friends

I'm working on an embedded linux QT 4.7.3 video application.

I have a video widget which is nothing but a pixmap holder and it paints the continuous feed of images which looks like a video widget to user. I'm painting my video widget @30 fps (in approx 33 msec) with a call to QWidget::update() method.

Everything is working fine as I want. But the CPU usage is tooooo high for my QT application. I ran the 'very sleepy' tool and "here is the output of a sample" [http://i44.tinypic.com/2n8v2b5.jpg]

!http://i44.tinypic.com/2n8v2b5.jpg(very sleepy sample)!

From the sample its obvious that Qt4 libraries uses 80% of CPU time.

Can you please suggest me to reduce the CPU usage ?

kqt-mr-nv6

what images are you painting
what is the format and pixel density

URPradhan

Thank you for your reply.

I'm creating a QImage->QPixmap from the image data I got from my cam
I'm not sure about the image format and density but I get the feed from the camera using the h263/h264 codec

And from the very sleepy data I'm not sure why QGraphicsView::QGraphicsView:() and QFutureInterfaceBase::isRunning() is taking so much time, where I'm not calling them explicitly.

kqt-mr-nv6

JPEG is a compressed image format
if you are handling conversion of high pixel density to/from raw
processor load is implicit

URPradhan

^I have updated the previous post with image format. And note that the image creation and processing it from the camera feed does not take too much CPU but the paint takes huge chunk of it.

If I only comment the line with [QWidget::]update(), the CPU usage drops drastically. So its the paint only taking too much CPu cycles.

kqt-mr-nv6

do you have a GPU on board

URPradhan

No GPU on board on my device, but the USB camera has which captures the feed and broadcast it.

kqt-mr-nv6

OpenCV libraries are optimized to do such tasks
you have direct support to capture and show videos
you can integrate OpenCV with QT

URPradhan

I really appreciate your suggestion.
But I'm not able to understand, how OpenCV will solve my problem ?

My problem is not in CPU cycles consumed for image capturing/creating rather the problem is in painting the captured images with QT and QtGui libraries takes huge amount of CPU cycles to paint the images.

kqt-mr-nv6

On devices with no hardware acceleration, Qt will use QRasterPaintEngine, which handles the acceleration using software. On devices supporting OpenGL ES, OpenVG or DirectFB(not supported by Windows CE), Qt will use the respective paint engines to accelerate painting. However, hardware configurations that only support a limited set of hardware acceleration features, might slow the application graphics down rather than speeding it up when using unsupported operations that must fall back to the raster engine.

check this for more info
"http://harmattan-dev.nokia.com/docs/library/html/qt4/qt-embeddedlinux-accel.html":http://harmattan-dev.nokia.com/docs/library/html/qt4/qt-embeddedlinux-accel.html

URPradhan

Thank you for the link.

But unfortunately my target h/w does not have an dedicated GPU and I can't use other paint engines.

I'm still not convinced why the QtGui library takes so much time to paint. Is there any other way around to reduce the CPU usage for continuously painting the images for a video widget ?