POV-Ray : Newsgroups : povray.beta-test : Highlight bug Server Time
30 Jun 2022 12:11:57 EDT (-0400)
  Highlight bug (Message 1 to 8 of 8)  
From: Rune
Subject: Highlight bug
Date: 28 Sep 2001 15:27:04
Message: <3bb4cf08@news.povray.org>
When normals are used, highlights are sometimes visible where they should be
in shadow. I think a similar bug existed for reflection in POV-ray 3.0 but
it was fixed. It was not fixed for highlights though. The following scene
shows visible highlights from a light that is on the opposite side of the
surface than the camera. Clearly that should be fixed.

Can someone please confirm this bug?

// camera in front of box:
camera {location -2.5*z look_at 0}
// light_source behind box:
light_source {1000*z, color 1}
background {color <0.6,0.8,1.0>}
box {
   <-1,-1,0>, <1,1,0>
   pigment {color rgb 0}
   normal {bumps 6 scale 0.2}
// phong and specular shows up ???
   finish {phong 1}
}

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated June 26)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk


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From: Bob H 
Subject: Re: Highlight bug
Date: 28 Sep 2001 17:57:19
Message: <3bb4f23f@news.povray.org>
"Rune" <run### [at] mobilixnetdk> wrote in message
news:3bb4cf08@news.povray.org...
> When normals are used, highlights are sometimes visible where they should
be
> in shadow. I think a similar bug existed for reflection in POV-ray 3.0 but
> it was fixed. It was not fixed for highlights though. The following scene
> shows visible highlights from a light that is on the opposite side of the
> surface than the camera. Clearly that should be fixed.
>
> Can someone please confirm this bug?

Yes, I see it too.  If the box is using    <-1,-1,0>, <1,1,0.000001>
instead then the highlighting vanishes.  Add another decimal place and it
reappears.  The plane and disc also have it, I couldn't get a cylinder to
show it, whether by scale or base and top narrowing.  Only generates
degenerate apex error, presumably before it gets sufficiently thin(?).
Unless plane, box, disc are somehow related and other primitives might not
be, which I wouldn't know anyway.

A very flat sphere won't show it, so I take it this is a problem confined to
just these type objects? (triangles too, etc.)

Bob H.

> // camera in front of box:
> camera {location -2.5*z look_at 0}
> // light_source behind box:
> light_source {1000*z, color 1}
> background {color <0.6,0.8,1.0>}
> box {
>    <-1,-1,0>, <1,1,0>
>    pigment {color rgb 0}
>    normal {bumps 6 scale 0.2}
> // phong and specular shows up ???
>    finish {phong 1}
> }
>
> Rune
> --
> 3D images and anims, include files, tutorials and more:
> Rune's World:    http://rsj.mobilixnet.dk (updated June 26)
> POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
> POV-Ray Webring: http://webring.povray.co.uk
>
>


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From: Rune
Subject: Re: Highlight bug
Date: 28 Sep 2001 18:35:37
Message: <3bb4fb39@news.povray.org>
"Bob H." wrote:
> Yes, I see it too.

Thanks for confirming it.

> If the box is using    <-1,-1,0>, <1,1,0.000001>
> instead then the highlighting vanishes.

Yes, as I understand it, the problem is that the normal pertubation makes
the "highlight ray" (in some ways similar to a reflected ray) go *through*
the surface when it should be confined to one side from where it came.

However, if the "highligt ray" is blocked by *another* surface, then it
really is blocked - as it should be.

A box of zero depth works as just a single surface. The effect can be seen
with any object, provided that no surfaces are blocking the "highlight ray".
For example you can also get the effect with a sphere if you place the
camera outside the sphere and the light_source inside the sphere.

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated June 26)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk


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From: Bob H 
Subject: Re: Highlight bug
Date: 28 Sep 2001 18:50:47
Message: <3bb4fec7@news.povray.org>
"Rune" <run### [at] mobilixnetdk> wrote in message
news:3bb4fb39@news.povray.org...
>
> Yes, as I understand it, the problem is that the normal pertubation makes
> the "highlight ray" (in some ways similar to a reflected ray) go *through*
> the surface when it should be confined to one side from where it came.
>
> However, if the "highligt ray" is blocked by *another* surface, then it
> really is blocked - as it should be.
>
> A box of zero depth works as just a single surface. The effect can be seen
> with any object, provided that no surfaces are blocking the "highlight
ray".
> For example you can also get the effect with a sphere if you place the
> camera outside the sphere and the light_source inside the sphere.

Okay, I was going to check on that too and saw this first.  Figured it
probably was something of a single surface thing.

Checking on interior_texture just now gets rid of it, even if empty.
Related perhaps?

Bob H.


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From: Peter Popov
Subject: Re: Highlight bug
Date: 29 Sep 2001 15:42:19
Message: <cnvartgujvtlb03lkr44tl53joghtpnc03@4ax.com>
On Fri, 28 Sep 2001 21:23:55 +0200, "Rune"
<run### [at] mobilixnetdk> wrote:

>When normals are used, highlights are sometimes visible where they should be
>in shadow. I think a similar bug existed for reflection in POV-ray 3.0 but
>it was fixed. It was not fixed for highlights though. The following scene
>shows visible highlights from a light that is on the opposite side of the
>surface than the camera. Clearly that should be fixed.

Isn't this the Shadow Line problem Warp describes in the VFAQ?


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg


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From: Rune
Subject: Re: Highlight bug
Date: 29 Sep 2001 15:55:35
Message: <3bb62737@news.povray.org>
"Peter Popov" wrote:
> Isn't this the Shadow Line problem Warp describes in the VFAQ?

No.

The shadow line problem is about absence of diffuse lighting where it is
supposed to be.

This problem is about presence of highlights where they shouldn't be.

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated June 26)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk


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From: Warp
Subject: Re: Highlight bug
Date: 29 Sep 2001 16:38:59
Message: <3bb63162@news.povray.org>
Rune <run### [at] mobilixnetdk> wrote:
: The shadow line problem is about absence of diffuse lighting where it is
: supposed to be.

: This problem is about presence of highlights where they shouldn't be.

  Technically they are caused by the same thing: The lighting model used
in POV-Ray (which is based on normal vectors).

  (Of course this makes it sound like there's something wrong with this
lighting model and that it's exclusive to POV-Ray. It's not so - this
lighting model is almost the only one used in any renderer.)

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -


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From: Rune
Subject: Re: Highlight bug
Date: 29 Sep 2001 17:35:33
Message: <3bb63ea5@news.povray.org>
"Warp" wrote:
>   Technically they are caused by the same thing:
> The lighting model used in POV-Ray (which is based
> on normal vectors).

I know that.

But while the shadow line problem is problematic to fix, the highlight bug
should be pretty easy to fix.

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated June 26)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk


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