Fill Slice Views without Changing Image Spacing

Support
14

@lassoan, I’ve looked into the FOV resetting and found that the vtkMRMLSliceLogic is checking the aspect ratio of the window against the pane AR here

How do you feel about the following modification proposal?

  double windowAspect = (newWidth != 0. ? newHeight / newWidth : 1.);
  double planeAspect = (newFOV[0] != 0. ? newFOV[1] / newFOV[0] : 1.);
  double oldWindowAspect = (oldDimensions[0] != 0. ? oldDimensions[1] / oldDimensions[0] : 1.);
  double oldPlaneAspect = (oldFOV[0] != 0. ? oldFOV[1] / oldFOV[0] : 1.);
  if (windowAspect != planeAspect && oldWindowAspect == oldPlaneAspect)
    {
    newFOV[0] = (windowAspect != 0. ? newFOV[1] / windowAspect : newFOV[0]);
    }

This way the newFOV is corrected only if the user/dev did not change the aspect ratio of the slice view. If the aspect ratio is custom, there is no correction of the AR. While on a custom AR, if the user clicks center to volume on sliceviewcontroller, the AR returns to the original one.
I find it minimally invasive and it keeps the current behavior for the standard not distorted AR. If you think is a good idea I can open a PR for this.
This fix does not perform the behavior I want for the use case above, but the changes I need to apply to the FOV are less dramatic, improving the overall user experience.
Thank you very much.