Hopefully I'm missing something, but it looks to me like QwtPointMapper::toImage() will never use threads.

I'm trying to plot a large number of points using a QwtPlotCurve with the Dots style. While stepping through the code in debug I noticed that QwtPointMapper::toImage skipped the QFuture/QtConcurrent code based on a preprocessor check, "#if QWT_USE_THREADS".

I don't see any way for this check to pass. The only define for QWT_USE_THREADS that I can find is at the top of qwt_point_mapper.cpp :
Qt Code: 
  1. #if !defined(QT_NO_QFUTURE)
  2. #define QWT_USE_THREADS 0
  3. #endif
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If QT_NO_QFUTURE isn't defined then QWT_USE_THREADS = 0, and if QT_NO_QFUTURE is defined then QWT_USE_THREADS is not defined. Either way it seems that a subsequent check, "#if QWT_USE_THREADS", will fail.

Am I misinterpreting the logic?