Re: 'nohidden3d' option behavior

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

On 05/23/2016 06:35 PM, Ethan A Merritt wrote:
> On Monday, 23 May, 2016 18:24:39 Daniel J Sebald wrote:
>> I've read through the documentation for the option "with ...
>> nohidden3d".  My initial understanding of the nohidden3d option is that
>> it could be a means to individually select what items are included in
>> hidden line removal:
>>
>> "
>>    As of gnuplot version 4.6, hidden3d also affects 3D plotting styles
>> `points`,
>>    `labels`, `vectors`, and `impulses` even if no surface is present in
>> the graph.
>>    Unobscured portions of each vector are drawn as line segments (no
>> arrowheads).
>>    Individual plots within the graph may be explicitly excluded from this
>>    processing by appending the extra option `nohidden3d` to the `with`
>> specifier.
>> "
>>
>> I'm not sure how "even if no surface is present in the graph" is to be
>> interpreted.  I take it to mean there is something in plots, currently,
>> other than surfaces which can have a 2D subspace that obscures the
>> visual field.
>>
>> More than that though is this phrase "excluded from this processing".
>> It's ambiguous as to what "this processing" applies to.
>
> I'll reply in more detail later, but for now the key thing is that
> "this processing" means "sorted together on depth (distance from viewer)".
> I.e. even if there are no surfaces to obscure pieces of a vector,
> it may still be useful to sort the vectors so that the close ones are
> drawn on top of the further ones.

OK, I suppose that makes sense.  Typically I think of the hidden3d 
processing as bisecting or segmenting, but yeah it could be useful to 
order things.


> If you attach the "nohidden3d" attribute to something then it isn't sorted
> on depth.  All elements of that unsorted plot will appear in the same layer
> (could be in front of; could be behind) the objects that were sorted together.

Meaning that the lines of linespoints are disappearing because somehow 
the algorithm thinks the lines are fully obscured because at every 
endpoint of the line is covered by a point?  Hence, there are only 
points left and no edges so the error message?

I just altered the code to allow LINES to go on through to the rest of 
the nohidden3d list.  That still produces an error even though there are 
no obscuring points coinciding with the lines:

[ALTERED CODE RESULT]
gnuplot> set samples 20
gnuplot> set hidden3d
gnuplot> splot 20*sin(x*y)/(x*y) with lines nohidden3d
          *All* edges undefined or out of range, thus no plot.

Well, I can work around the use of "nohidden3d" for what I'm programming 
by adding some extra logic; it's just that it would be convenient if 
nohidden3d applied to lines.

Dan