Re: surface elements for transparent_solids.dem

[Ethan M. <merritt@u.washington.edu>]

On Wednesday 10 January 2007 22:50, Daniel J Sebald wrote:
> > 
> >>One thing I notice when the fill is solid is that along some of the
> >>edges of the Kuen's surface example are some oddly shaped surface
> >>elements.
> 
> I'm pretty certain this is a bug; there are some elements from a hidden
> surface for some reason being mixed in with the elements from the visible
> surface.  Hidden lines works as it should. 


The "depthorder hidden3d" option of pm3d is just plain different from the 
"set hidden3d" code. They will not, in general produce the same result.  
The "set pm3d depthorder" doesn't really calculate hidden lines or surfaces 
at all (please see docs); it just sorts the quadrangles based on the mean 
W-coordinate of each, and draws them in order of increasing W. 
"W" here is the virtual axis from the center of the plot to your eye.  
Because it uses the mean W of the whole tile to make a call for the entire tile, 
you can get misplaced corners if the protrude above/below the mean W of the 
next tile in view.  C'est la vie.

Please see also the previous extensive discussion and argument with regard 
to patch #1077726 from Nov 2005.









> To verify this, run the 
> transparent_solids.dem file three times in X11 creating a new window each
> time so the various Kuen surface plots can be compared.
> 
> load 'transparent_solids.dem'
> (hit return twice)
> (
> change
>   splot x(u,v), y(u,v), z(u,v) with pm3d
> to
>   splot x(u,v), y(u,v), z(u,v) with lines
> in transparent_solids.dem'
> )
> set term x11 2
> load 'transparent_solids.dem'
> (hit return twice)
> (
> add
>   unset hidden3d
>   splot x(u,v), y(u,v), z(u,v) with lines
> in transparent_solids.dem'
> )
> set term x11 3
> load 'transparent_solids.dem'
> (hit return twice)
> 
> I believe the second plot with hidden lines but no pm3d elements looks
> correct.  Now, if one looks at the third plot with the quadrangles from
> what would be hidden surfaces, these match the geometry of the few
> quadrangles in the first "hidden3d pm3d" plot.
> 
> It would be nice to fix this for 4.2 (don't want the flagship figures hilighting flaws).  This seems like it would be but a line or two alteration.  Anyone?
> 
> Dan
> 
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