return valid marker. If not -- let blender crash, because that means
something went really bad and silencing this isn't good idea.
Also made mask parenting to tracking data aware of clip's start frame.
- Remove clip/mask specific size/aspect getters, they shall just
use the same size/aspect ratio.
- Made size getter (and some other public functions) accept context
instead of SpaceClip. Currently only SpaceClip is being get from
this context, but later it'll be helpful when adding support of
editing mask without opening clip in clip editor (in this case
using render resolution for mask would be ideal, but this
requires knowing scene in size getter).
- Rearrange some functions in clip_editor.c for easier navigation
in the file.
whether getting of some property happens or this property is
being changed.
Also made it more clear whether affecting property belongs
to clip or mask datablock.
- Re-arrange functions in headers and implementation file to make them
more grouped by entity they're operating with. Also order of functions
in implementation file should match order of functions in header for
easier navigation.
- Rename some functions to match conventions of naming public functions.
- Some code de-duplication, still some room for improvements tho.
- Split main 2D tracking functions into smaller steps to make it more clear.
Accidentally OpenMP was disabled in some of previous commits, re-enable it.
