I found a the following solution.
I simply use the QImage as my rendering space and export that image. Drawing is still done with a QPainter and the QQuickPaintedItem is only used to display the image for the user.
QML Items like a Label are drawn via QPainter onto the QImage surface via
QImage image; QPainter painter(&image); painter.setPen("#FFFFFF"); painter.setFont(QFont("Helvetica", 15)); int x = 20; int y = 20; painter.drawText(x,y, "Hello World"); painter.done();For more generic use I provide a paint(QPainter & painter, int x, int y, QSize resolution) interface in C++ for each "rendered object" as alternative compared to a Q_OBJECT where the rendering is provided by Qt.
This looks like this:
class Renderer : public QObject { ... Q_SLOT void processImage(const QImage image) { _image = image.copy(); QPainter painter; painter.begin(&_image); _draw_fps_text(painter); ... painter.end(); } Q_SLOT void setFPSOptions(const QList<FPSOptions> fpsOptionsList) { _fps_options_list = fpsOptionsList; } void _draw_fps_text(QPainter & painter) { int video_count = _get_video_count(); int image_width = _image.size().width(); int image_height = _image.size().height(); for(int i = 0; i < _fps_options_list.size(); ++i) { int x_padding = static_cast<int>(image_width / 28); int x_step = static_cast<int>(image_width / video_count); int y_step = static_cast<int>(image_height / 15); int x = x_padding + x_step * i; // width int y = y_step; // height _fps_options_list[i].paint(painter, x, y, image.size()); } }My rendering pipeline changed from
VideoCapture -> (frame) -> Processing -> (QImage, data) -> QML Viewer -> (Grab QImage from View) -> Exporter -> (IO)to
VideoCapture -> (frame) -> Processing -> (QImage, data) -> Renderer -> (QImage) -> Exporter -> (QImage) + (IO) -> QML ViewerThe Exporter currently pipes the QImage to the QML Viewer as it's currently impossible to let a QML Object run in another thread. The optimal solution would be to duplicate the output of the Renderer to both Exporter and QML Viewer, see this thread.
