OpenGL rendering to a specifc QML item

blueskin.neo

Hi,
I have a QML file which contains a layout of QML items and now I want one of those items to be a QGLWidget. i.e. I want to render to a specific QML item.

Is anyone aware of how to do this? Thank you.

CV

minimoog77

I don't think it's possible, but you could use FBO instead.

mbrasser

Hi,

I'd suggest setting the viewport of your QDeclarativeView to a QGLWidget. You can then use GL within your item's paint() method. (typically using QPainter::beginNativePainting() and QPainter::endNativePainting()). Is this type of approach viable for what you need to do?

Regards,
Michael

blueskin.neo

Hi Michael,

If I set the viewport to QGLWidget then the entire DeclarativeView becomes the paint area right. i.e. when I paint inside QGLWidget::paintGL() then I'd be painting to the whole view and not a specific region (i.e. QDeclarativeItem).
I have a list of QDeclarativeItems from MyQDeclarativeView.rootObject()->children();
And trying to figure out how I can make one of these items as a paint area for my GLWidget.
Thanks for your reply.

CV

blueskin.neo

Hi Michael,

I am kind of successful but not completely, I created a new DeclarativeItem and set its graphicsproxywidget's widget to my glwidget as below

@class GLWidgetDeclarativeItem : public QDeclarativeItem
{
Q_OBJECT
public:
GLWidgetDeclarativeItem(QDeclarativeItem *parent =0)
: QDeclarativeItem(parent)
{
setFlag(QGraphicsItem::ItemHasNoContents, false);
QDeclarativeItem::setFlag(QGraphicsItem::ItemHasNoContents, false);
m_glWidget = new GLWidget();
m_proxy = new QGraphicsProxyWidget(this);
m_proxy->setWidget(m_glWidget);
m_glWidget->show();
m_proxy->show();
}

private:
GLWidget *m_glWidget;
QGraphicsProxyWidget *m_proxy;
};
@

And in my main when I create a declarativeview, I find the QML item and pass it as parent to GLWidgetDeclarativeItem as
@
int main(int argc, char argv[])
{
QApplication app(argc, argv);
QDeclarativeView qmlview (QUrl::fromLocalFile("qml/GLInsideQML/main.qml"));
QDeclarativeItem item = qobject_cast<QDeclarativeItem>
(qmlview.rootObject()->findChild <QObject> ("GLArea"));
GLWidgetDeclarativeItem glItem(item);
qmlview.show();
return app.exec();
}
@

Now, the only problem is I don't see the painting happening, I get the mouseEvents invoked in my GlWidget when I click. But no painting :(
"Here's the complete test code":https://sites.google.com/site/blueskinneo/home/GLInsideQMLTest.zip?attredirects=0&d=1
Let me know if you find anything wrong.

Thanks
CV

mbrasser

Hi,

[quote author="blueskin.neo" date="1318962508"]
If I set the viewport to QGLWidget then the entire DeclarativeView becomes the paint area right. i.e. when I paint inside QGLWidget::paintGL() then I'd be painting to the whole view and not a specific region (i.e. QDeclarativeItem).[/quote]

You shouldn't need to worry about QGLWidget::paintGL() if you are creating a single custom item. You can use raw GL inside of your QDeclarativeItem subclass' paint() function instead (wrapped in the calls I mention above), as long as the viewport for the view is a QGLWidget.

Here are a couple other threads that might explain this a bit better:

Hope that helps.

Regards,
Michael

diro

[quote author="blueskin.neo" date="1318962508"]Hi Michael,

If I set the viewport to QGLWidget then the entire DeclarativeView becomes the paint area right. i.e. when I paint inside QGLWidget::paintGL() then I'd be painting to the whole view and not a specific region (i.e. QDeclarativeItem).
I have a list of QDeclarativeItems from MyQDeclarativeView.rootObject()->children();
And trying to figure out how I can make one of these items as a paint area for my GLWidget.
Thanks for your reply.

CV[/quote]
I agree with mbrasser!
In my real project, the painting could be restricted in the specific region. I created a C++ extension inherited from QDeclarativeItem (so, it is QGraphicsItem rathan than QGLWidget), and the extension works well with opengl native commands. I just overwrite the paint() function in QDeclarativeItem, not the paintGL() in QGLWidget.