Re: [ 1004754 ] Tics and grid slightly outside border.

[Daniel J S. <dan...@ie...>]

Ethan Merritt wrote:
> On Wednesday 28 June 2006 08:07 am, Petr Mikulik wrote:
> 
>>>I've placed a patch under bug report [ 1004754 ] on SourceForge
>>>that is a cleanup of the tic generation.  I think it would be worth
>>>considering for 4.2, because it does fix the bug and it is much
>>>friendlier computer math
>>
>>I propose to commit it.
>>
>>Notes: "logorithm" => "logarithm"
> 
> 
> I have not analyzed the code itself, and don't have time to 
> do so right now.  But the cover explanation contains an 
> off-by-one error in the algorithm, so I worry that it is not
> correct.

That is fine in this new layout.  It's explained in the note.  (But if you are uncomfortable with it, leave it out for now.)

I will use [ ] to signify range (i.e., lmin and lmax), and I will use T to be major tic and t to be minor tic.


             [                           ]

t       T       t       t       t       t       T       t

        ^                                       ^
      start                                   outside

i_tic=  0       0       0       0       0       1       1     ...



The scheme is to first "integerize" the major tics where "start" will be the case of i_tic = 0.  (I should say, that we don't round the upper limit upward anymore, but downward because if it is outside of the range, it isn't printed.)  In this case N_start and N_end are the same.  We only need one interval and minor tics.

Imagine the case of moving that upper range "]" so that it equals a major tic.  Well in that case, with the rounding downward (floor) it will be that N_end = N_start + 1, and we'll get two intervals of major tic and minor tics.  (The minor tics will be outside the range and not printed, but that is the idea.)

Dan