[Solved] Rendering QImage on QGLWidget of QML plugin

[karlphillip]

I'm trying to write a QML plugin that reads frames from a Video (using a custom widget and NOT QtMultimedia/Phonon), then each frame is converted to a QImage with format RGB888, and then displayed on a QGLWidget. Right now nothing seems to be draw on the screen (the screen stays white).

It's important to state that I already have all of this working without QGLWidget, so I know the issue is setting up and drawing on QGLWidget.

The plugin is being registered with:

@qmlRegisterType<Video>(uri,1,0,"Video");@

so Video is the main class of the plugin. On it's constructor we have:
@
Video::Video(QDeclarativeItem* parent)
: QDeclarativeItem(parent), d_ptr(new VideoPrivate(this))
{
setFlag(QGraphicsItem::ItemHasNoContents, false);

Q_D(Video);
QDeclarativeView* view = new QDeclarativeView;
view->setViewport(&d->canvas()); // canvas() returns a reference to my custom OpenGL Widget

}@

Before I jump to the canvas object, let me say that I overloaded Video::paint() so it calls canvas.paint() while passing QImage as parameter, I don't know if this is the right way to do it so I would like some advice on this:

@void Video::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
Q_UNUSED(painter);
Q_UNUSED(widget);
Q_UNUSED(option);

Q_D(Video);
// I know for sure at this point "d->image()" is valid, but I'm hiding the code for clarity
d->canvas().paint(painter, option, d->image());

}@

The canvas object is declared as GLWidget canvas; and the header of this class is defined as:

@class GLWidget : public QGLWidget
{
Q_OBJECT
public:
explicit GLWidget(QWidget* parent = NULL);
~GLWidget();

void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QImage* image);

};@

Seems pretty simple. Now, the implementation of QGLWidget is the following:
@
GLWidget::GLWidget(QWidget* parent)
: QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
{
// Should I do something here?
// Maybe setAutoFillBackground(false); ???
}

GLWidget::~GLWidget()
{
}@

And finally:

@void GLWidget::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QImage* image)
{
// I ignore painter because it comes from Video, so I create a new one:
QPainter gl_painter(this);

// Perform drawing as Qt::KeepAspectRatio

gl_painter.fillRect(QRectF(QPoint(0, 0), QSize(this->width(), this->height())), Qt::black);

QImage scaled_img = image->scaled(QSize(this->width(), this->height()), _ar, Qt::FastTransformation);

gl_painter.drawImage(qRound(this->width()/2) - qRound(scaled_img.size().width()/2),
qRound(this->height()/2) - qRound(scaled_img.size().height()/2),
scaled_img);
}@

What am I missing?

[karlphillip]

The answer for this question "is here":http://stackoverflow.com/a/8488275/176769.

[koahnig]

Welcome to devnet

Thanks for sharing the solution. Please mark the title line with [Solved]. This helps others to see that there is a solution available, if they have a similar question.