Re: large values outside fixed scale

[Uwe R. <Uwe...@ti...>]

On Saturday 21 July 2007 00:27, Chris Cortopassi wrote:

> I've been using Qwt with great success for a software oscilloscope
> application, but I've had trouble recently trying to implement large scale
> factors (resulting in large values clipped off the plot).  The code below
> will crash on Windows XP with Qt4.3.0.  Although behavior is still strange,
> it doesn't crash on Win Qt4.2.3 nor Linux (Qt 4.2.3 or 4.3.0). 

For painting a curve all points are mapped into coordinates of the paint 
device ( here the plot canvas). For Qt3 compatibility Qwt still uses 
integers. ( Of course Qt4 would also has to map to integers for paint devices 
like a X11 widget - only devices like PDF can make use of floats ).

Your points are so far below/above the visible area, that the coordinates are 
below/above the range of an integer. I checked  {-2e8,  2e8} on Linux/X11 and 
qRound simply maps the x-values to { 0, 0 }.

I didn't check on Windows, but in general the raster paint engine is the most 
unstable one, because it is a home brew implementation - not only a frontend 
to one of the stable native graphics subsystems. I guess if you print to a 
QImage on X11, you will notice similar effects/crashs like on Windows.

> I realize
> this isn't quite standard usage, but can you please provide any insight,
> workarounds, known limitations, etc.  Could this be a bug in Qt and/or Qwt?

Well, the problem in the Qwt code will disappear as soon as I use qReal 
instead of ints. But this has no high priority for me.

Uwe