Re: bug in depthorder?

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

Petr Mikulik wrote:
>>>The enclosed script using the "pm3d depthorder" gives wrong ordering of
>>>faces on gnuplot-cvs, and sometimes wrong and sometimes good ordering on
>>>gnuplot 4.2. Also try to rotate the plot by mouse. How can this happen?
>>
>>Petr,
>>
>>depthorder is a very much an approximation to true hidden surface features.  I
>>think there was some discussion a couple years ago about this.  If I'm
>>remembering correctly, I wrote a patch for determining the depth which I
>>thought was a bit more robust.  But after discussions with Ethan, I thought it
>>would be more worthwhile putting effort into actual hidden surface, if one had
>>time.  (A generalization of the hidden lines code where a hidden surface is
>>broken into smaller parts.)
>>
>>The problem in your example is that the surfaces are too big relative to the
>>resolution such that in 3D space their depths overlap.  Furthermore, this
>>example is probably undersampling anyway because the peaks aren't visible.
> 
> 
> I was wondering which point(s) of the rectangle is/are used for the depth 
> ordering. Is it min(all 4 corners) or center-of-rectangle or all of them? It 
> seems to me that this is producing this bug: the two problematic rectangles 
> touch in one edge (2 corners), but their other 2 corners have different 
> depth.

You've found the right issue.  It is min or max, I can't recall which.  I think I'd written a patch that used average or something.  All choices have their particular problem scenarios.

Dan