BREAKING: MaskGenerators now return masks as const.
Reason: There is no guarantee of the returned instance is "owned" by
the reciever and is dependent from other data items. So one can
use it, but should not directly manipulate it.
How To migrate: Option 1: improve your const correctness (very often
a const access is sufficient. Option 2: If you realy need to own/manipulate
the mask, then clone it.
+ Fixed T29239
- fixed the correct mapping of time point to time step of mask
- Avoid cloning of images in Mask generator
- Improved const correctness and const support in some statistic classes