[Qt-interest] Using OpenGL to render and transform a SVG in a QDialog

[Sven Grunewaldt]

Hi,

I need to show a SVG graphic which resembles a compass needle. This
graphic will be rotated several times per second, so to keep this at
least a little bit with good performance I thought about using a
QGLWidget since OpenGL should be able to render a vector graphic pretty
easily.

The QtSvg documentation states:
Using QSvgRenderer, Scalable Vector Graphics (SVG) can be rendered onto
any QPaintDevice subclass, including QWidget, QImage, and QGLWidget.

I tried to implement this with a simple class which extends QGLWidget
and reimplements the paintEvent:
SvgGLWidget::SvgGLWidget(QString svgFile, QWidget *parent) :
	QGLWidget(parent)
{
	renderer = new QSvgRenderer(svgFile, this);
}

void SvgGLWidget::paintEvent(QPaintEvent *event)
{
	QPainter painter(this);
	renderer->render(&painter);
	painter.rotate(100);
}

The SVG is indeed rendered correctly, but the rotate(100) does not work
at all. I guess I'm just missing something here or just do it the wrong
way(TM).

Is this the correct way to render a SVG which will be rotated several
times per second? Why does the rotate() method not work?

Regards,
Sven Grunewaldt