Allow to locking colorbar scale to be symmetric around zero

[PierreRaybaut]

Issue originally submitted here: https://code.google.com/p/guiqwt/issues/detail?id=69

Reported by HamfBohne, May 11, 2015

For certain types of data it is important to be able to compare sign of different features in an XYImageItem object. Being able to lock the color axis to be symmetric around zero would help with that quite a lot. An interface like the "Reverse Y axis" checkmark or an entry in the axis' properties would be ideal.

This feature would need to be then respected by the automatic contrast adjustment (great tool by the way) to be really valuable.

Version

Current python(x,y) on Windows. guidata 1.6.1, guiqwt 2.3.1

[PierreRaybaut]

I'm not sure I understand your request. A code example would be necessary I think.