spectrogram questions

[Uwe]

You can easily reproduce the crash with the "rasterview" example, the binary will crash at startup

Indeed the raster paint engine is running on a nullptr for the color map of the backing store of the canvas. It happens in convertIndexedToARGB32PM painting/qdrawhelper.cpp.
Seems like there is a bug, when drawing an Indexed8 QImage to a QPixmap. But as this does not happen with the spectrogram example it needs more investigation, what additional side effects are relevant here.

Like expected the problem does not happen, when using the X11 paint engine, that has been reintroduced with Qt 5.10. Using the X11 paint engine is recommended for all type of vector data ( curves ) as it makes use of hardware acceleration - in opposite to the raster paint engine, that is a pure software renderer. X11 can be enabled with "export QT_XCB_NATIVE_PAINTING=1" ( or "export QT_GRAPHICSSYSTEM=native" with Qt4 ).

Using X11 for a spectrogram ( or other raster data ) does not make the same difference as for vector data, beside you are running remote X11.
Note, that using setMaxRGBTableSize is not affected by this problem, as it does not create a Indexed8 image.

But anyway - there is a crash in the raster paint engine, that needs to understood. Maybe I can find a workaround and/or create a bug report for Qt, but it is kind of random when Qt development does fixes.

Uwe

[embeddedmz]

I set DEBUG_RENDER to 1 and compiled/tested Qwt in debug and release mode but qDebug won't work ! any idea how to fix that ? (the stuff in StackOverflow is outdated...) I could change qDebug by std::cout, but I want to know why this kind of stuff doesn't work when needed

[Uwe]

But anyway - there is a crash in the raster paint engine, that needs to understood.

Bug is understood now and a fix/workaround has been added to all versions of Qwt >= 6.1

Uwe

[embeddedmz]

Cool are the bugfixes included in the qwt downloaded via :

svn export svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1

svn export svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1

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