ENH: Added new volume rendering quality option: Normal
SetLockSampleDistanceToInputSpacing usually provides good quality rendering at acceptable speed, but on slow computers or in virtual reality views (where very high frame rate is needed), it is still necessary to allow choose between volume rendering speed and quality.
Added a new option to clearly distinguish between quality settings:
- adaptive: sampling computed from desired fps
- normal: sampling computed from input volume
- maximum quality: sampling computed from input volume, with 10x oversampling