Re: From the discussion of patch #1723715

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Ethan Merritt wrote:

> If this is a problem, I suggest that the proper answer is to move the grid
> settings out of (struct axis) into a new self-contained structure.  I may
> be overlooking something, but I don't see why the grid needs to be a
> property of the axis at all.

The grid effectively is a property of the axis, as can clearly be seen 
by the way we control it: the majority of grid options have a reference 
to some axis in their command syntax.

We grid based on tics, which are elements obviously linked to an axis. 
As it is, drawing the grid needs a reference to the axis' tic 
definitions, its terminal mapping and lots of other things.  In other 
words, it needs almost the entire axis struct.

The axis struct is designed around the existing usage.  Redraw is new, 
and poses new requirements.  The axis struct will have to learn new 
tricks.  Splitting it up into separate sub-structs for range, tics and 
grid options would be the right step to start with.  That way, 'zoom' 
and friend can save/restore just the range, but leave grid settings alone.