On Sep 28, 2011, at 1:52 PM, ext Uwe Rathmann wrote: > On Wed, 28 Sep 2011 10:27:33 +0000, jens.bache-wiig wrote: > >> You have a valid point as I did not expect plots to be a major >> performance issue. I don't think anyone can make performance promises at >> this point but I would also not expect it to perform as fast as the >> current pipeline. On the other hand, being able to draw plot charts, >> within Qt Quick was a major reason for adding this API in the first >> place. > > Obviously you had business charts for nice presentations in mind, but you > find completely different type of use cases in the scientific or > engineering world. Especially in combination with Qt/Embedded there are > many, many applications displaying results from measurements ( often in > "realtime" ) - you can find even YouTube videos demonstrating them. But > Qwt is also used in GIS applications - think about displaying a > spectrogram for the elevation of a whole continent. > > Qwt is by far the oldest existing addon ( since Qt 1.1 in the 90s) and > has become the de-facto standard for plotting in the Qt world over the > years. I'm doing this package + all support since many years more or less > alone: > > When plot charts were really one of the major reasons for introducing Qt > Quick I'm more than surprised, that nobody ever contacted me to find out > what the real world use cases for a plotting widget are. > > Anyway ...
There is a misunderstanding here. The Canvas API from HTML was added so that one could do some imperative painting from QML/Javascript without having to go to C++. It is effectively a QPainter API. Though it could be used to render a plot API, I would not compare it to Qwt. Qwt is infinitely much more. I'm sorry for the confusion. > >> I also get the feeling that embedding Qt Quick inside Widgets might not >> be as straight forward as I thought, so I second Samuel's suggestion >> that just using your existing drawing code with a QImage might be the >> way to go. > > The plot canvas has its own backing store ( a QPixmap ) so - ignoring, > that I might loose any hardware acceleration - I could implement this > easily. But there are known use cases ( f.e. the oscilloscope ), where > this buffering needs to be turned off to get the required refresh rates. > > So when I get it right this all means that if an application needs a Qwt > plot with certain performance requirements it needs the QPainter API and > therefore can't use Qt-Quick in the complete application - at least as > long as embedding a QWidget into a QML application is not supported. And I do see us having this option available, long term. We think it is feasible, but have not implemented anything yet. And please keep in mind that QPainter is NOT going away. Ever. > > For all other type of plots I could offer a second path, where the plot > is rendered via QPainter/C++ and QImage/QSGItem to something Qt Quick > compatible and the application could make use of Qt Quick ? > > Isn't it possible to have an C++ API for the scene graph too - in the end > isn't it a problem of the API ( QML ) only and has nothing to do with the > new graphics pipeline ? There is public API. The most relevant classes are: http://doc.qt.nokia.com/qt5-snapshot/qsgitem.html http://doc.qt.nokia.com/qt5-snapshot/qsgpainteditem.html And if you want to implement your own scatter plot item you can use the raw scene graph API: http://doc.qt.nokia.com/qt5-snapshot/qsgnode.html http://doc.qt.nokia.com/qt5-snapshot/qsggeometry.html http://doc.qt.nokia.com/qt5-snapshot/qsgmaterial.html I would not be surprised if a scatter plot implemented using a geometry node would outperform QPainter > And what about the generation of documents ( mostly PDF ), what is one of > the key features of any good plotting library. Is this something I could > do with QML too or do I need to keep the QPainter based render code > because of this anyway ? I repeat: QPainter is NOT going away. Ever :) - Gunnar _______________________________________________ Qt5-feedback mailing list [email protected] http://lists.qt.nokia.com/mailman/listinfo/qt5-feedback
