POV-Ray : Newsgroups : povray.text.scene-files : parallel looks_like test scene Server Time: 14 Dec 2018 00:18:39 GMT
  parallel looks_like test scene (Message 1 to 3 of 3)  
From: Mike Horvath
Subject: parallel looks_like test scene
Date: 12 Sep 2016 14:43:01
Message: <57d6bef5@news.povray.org>
In this test scene the light source is stuck at the horizon when it 
should be up in the sky.

Mike


Post a reply to this message


Attachments:
Download 'looks_like_test.pov.txt' (4 KB)

From: clipka
Subject: Re: parallel looks_like test scene
Date: 12 Sep 2016 15:59:16
Message: <57d6d0d4$1@news.povray.org>
Am 12.09.2016 um 16:42 schrieb Mike Horvath:
> In this test scene the light source is stuck at the horizon when it
> should be up in the sky.

But the looks_like object is translated perfectly fine.


What you see is the highlight remaining unchanged; but the highlight
doesn't show where the light source's nominal position is -- it shows
the direction the light is coming from.

And that direction is unchanged: With a parallel light source, the
direction of all light rays depends only on the /relative/ location of
two points: The light source's nominal center and the point_at
parameter. But transformations act on both these points (I've just
checked the code), so a translation operation changes only the absolute
location of the points, not their relative location to one another. And
thus the light direction remains unimpressed.

(BTW, point_at defaults to <0,0,1>.)


Post a reply to this message

From: Mike Horvath
Subject: Re: parallel looks_like test scene
Date: 12 Sep 2016 16:44:46
Message: <57d6db7e$1@news.povray.org>
On 9/12/2016 11:59 AM, clipka wrote:
> And that direction is unchanged: With a parallel light source, the
> direction of all light rays depends only on the /relative/ location of
> two points: The light source's nominal center and the point_at
> parameter. But transformations act on both these points (I've just
> checked the code), so a translation operation changes only the absolute
> location of the points, not their relative location to one another. And
> thus the light direction remains unimpressed.
>
> (BTW, point_at defaults to <0,0,1>.)
>

Crap. I wish I'd known that. Now I have to go back through all my scenes 
and set point_at to <0,0,0>. Might want to mention this in the docs too. 
For instance, you might want to change this:

	Light source default values:
	LIGHT_TYPE        : pointlight
	falloff           : 70
	media_interaction : on
	media_attenuation : off
 >	point_at          : <0,0,0>
	radius            : 70
	tightness         : 10

Mike


Post a reply to this message

Copyright 2003-2008 Persistence of Vision Raytracer Pty. Ltd.