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In article <3974E13A.49899E8C@erols.com>, John VanSickle
<van### [at] erols com> wrote:
> This is what I tested; the normal does indeed need to be flipped to
> achieve this effect. I'm fairly sure this was done in a recent
> version of POV-Ray; I distinctly remember having to reverse the order
> of some defined points in order to get the normals pointed the right
> way.
I think the bug fix was added in 3.1b along with some double-illuminate
stuff:
"Fixed average normal bug and other normal flipping problems"
(revision.doc)
--
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/
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Chris Huff <chr### [at] maccom> wrote:
: I think the bug fix was added in 3.1b along with some double-illuminate
: stuff:
: "Fixed average normal bug and other normal flipping problems"
But flipping the normal vector of a (non-smooth) triangle is NOT a bug! It's
the right behaviour.
Think about a plane { y, 0 }. If you put a light source at y*10 it will
illuminate the top of the plane and the bottom will be shadowed. If you put
the light source at y*-10, it will be the other way around.
Now, this same behavior has to happen with regular triangles as well. If
the light source is at one side of the triangle, that side has to be
illuminated and the other shadowed. It doesn't matter which side.
To achieve this, the normal vector has to be flipped to point to the side
where the light source is. If the normal vector were pointing to the wrong
side, the side of the triangle which is facing the light source would be
shadowed, which is the wrong result.
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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Warp wrote:
>
> Chris Huff <chr### [at] maccom> wrote:
> : I think the bug fix was added in 3.1b along with some double-illuminate
> : stuff:
> : "Fixed average normal bug and other normal flipping problems"
>
> But flipping the normal vector of a (non-smooth) triangle is NOT a
> bug! It's the right behaviour.
> Think about a plane { y, 0 }. If you put a light source at y*10 it
> will illuminate the top of the plane and the bottom will be shadowed.
> If you put the light source at y*-10, it will be the other way around.
I was speaking of the calculations for normal patterns; the behavior
does seem to have changed since the 3.0 days.
Regards,
John
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In article <39756bd0@news.povray.org>, Warp <war### [at] tagpovrayorg>
wrote:
> Chris Huff <chr### [at] maccom> wrote:
> : I think the bug fix was added in 3.1b along with some double-illuminate
> : stuff:
> : "Fixed average normal bug and other normal flipping problems"
>
> But flipping the normal vector of a (non-smooth) triangle is NOT a bug!
> It's the right behaviour.
Umm, that's why it was added. Flipping the normal is the bug fix I was
talking about. Before, it wasn't done, and sometimes caused problems. :-)
--
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/
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Chris Huff <chr### [at] maccom> wrote:
: Umm, that's why it was added. Flipping the normal is the bug fix I was
: talking about. Before, it wasn't done, and sometimes caused problems. :-)
Oh, sorry. I got confused.
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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In article <39759DCA.E0B64DE7@erols.com>, John VanSickle
<van### [at] erolscom> wrote:
> I was speaking of the calculations for normal patterns; the behavior
> does seem to have changed since the 3.0 days.
There have been changes...and wasn't there a limitation on what patterns
could be used as normals in the 3.0.x versions? I think some of those
changes had to do with allowing any pattern to be used.
Anyway, there will be even more changes...check out MegaPOV for a
"preview" of what 3.5 should be like. Most of the changes have to do
with making the normal scale more reasonably, they now act much more
like actual surface deformations would.
--
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/
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