QImage to Qpixmap conversion is too slow

[Christian Ehrlicher]

@lansing said in QImage to Qpixmap conversion is too slow:

What is a faster way to do this?

Use a proper backend for your task. CPU raster is definitely not made for such kind of work. Use OenGL or similar instead.

[lansing]

@Christian-Ehrlicher said in QImage to Qpixmap conversion is too slow:

@lansing said in QImage to Qpixmap conversion is too slow:

What is a faster way to do this?

Use a proper backend for your task. CPU raster is definitely not made for such kind of work. Use OenGL or similar instead.

Is there any example with OpenGL? Like where do I start?

[SGaist]

Hi,

Can you give more information about how are these images created ? Passed around ?
Are they from a camera ?
Are you loading them from a file ?
Etc.

[lansing]

@SGaist

They were loaded from a video file, then go into a processor where it will spit out packed RGB data frame by frame.

I found a stackoverflow answer about passing the QImage into a QOpenGLWidget and then using its paintEvent to draw out the image, is this the way?

https://stackoverflow.com/questions/20245865/render-qimage-with-opengl

[SGaist]

What are you using to read your video file ?
Depending on that and the image format you could load the data directly into a texture and do the color space conversion in OpenGL rather than on the CPU side.

[lansing]

@SGaist said in QImage to Qpixmap conversion is too slow:

What are you using to read your video file ?
Depending on that and the image format you could load the data directly into a texture and do the color space conversion in OpenGL rather than on the CPU side.

That can be a future plan, but I want to do it one step at a time. For right now I need to know where to even start. The Qimage to QPixmap conversion is cutting my playback speed in half.

[mrjj]

@lansing
Hi
well try the OpenGLWidget::paintEvent code and see if its fast enough.
At least you don't have the conversion to pixmap

[lansing]

@mrjj

Hi This is what I have done so far:

class MyGLPainter : public QOpenGLWidget
{
    Q_OBJECT
public:
    MyGLPainter (QWidget *parent = nullptr);
    void paintEvent(QPaintEvent *) override;
    void drawImage(const QImage &image); 

private:
    QImage m_frameImage;

MyGLPainter::MyGLPainter (QWidget *parent): QOpenGLWidget(parent)  
{
}

void MyGLPainter::paintEvent(QPaintEvent *)
{
    QPainter painter(this);   
    painter.drawImage(m_frameImage.width(),m_frameImage.height(), m_frameImage);
    painter.end();
}

void MyGLPainter::drawImage(const QImage &image)
{
    m_frameImage = image;
    update();
}

But when I pass the image to drawImage(), the program will just crash. Am I doing this correctly?

[mrjj]

@lansing
Hi
It looks ok.
In what lines does it crash ?

[lansing]

@mrjj

At the line update(). It points to function QImage::operator=

[Christian Ehrlicher]

Do you update your image from a different thread? If so you should learn about threading: Threading Basics

[lansing]

@Christian-Ehrlicher

HI, is this related to the crash?

[mrjj]

@lansing

Hi
yes if you do it from another thread then very much yes.

[lansing]

@mrjj

I don't have threading in the program.

[mrjj]

@lansing
Hi
then something is wrong with the image then.
Else why crash on copy.

can you try with Image that you are 100% sure is valid ?

[lansing]

@mrjj

Hi, I have set the image to one in my resource folder for testing, now it has crashed at line m_frameImage = image. I have changed the image argument from const QImage & to QImage*, I don't know if that have a effect on it. But in debug, it did show my image dimension.

QImage *img= new QImage(":/cross.png");
myGLPainter->drawImage(img);

[mrjj]

@lansing
and it does still crash ?

[lansing]

Yes, it said

error: Debugger encountered an exception: Exception at 0x7ff71b7e9b88, code: 0xc0000005: read access violation at: 0xffffffffffffffff, flags=0x0

[Christian Ehrlicher]

@lansing said in QImage to Qpixmap conversion is too slow:

myGLPainter

Where do you initialize this variable?

[SGaist]

@lansing said in QImage to Qpixmap conversion is too slow:

QImage *img= new QImage(":/cross.png");
myGLPainter->drawImage(img);

That's the wrong thing to do as you will leak images doing so.

Beside the initialization issue pointed by @Christian-Ehrlicher can you provide the stack trace of your crash ?