On 9/12/2016 10:43 AM, Mike Horvath wrote:
> On 9/12/2016 7:56 AM, clipka wrote:
>> Am 12.09.2016 um 12:45 schrieb Jim Holsenback:
>>> On 9/11/2016 1:55 PM, clipka wrote:
>>>> Am 11.09.2016 um 16:23 schrieb Mike Horvath:
>>>>> Looks_like works fine with parallel lights as long as you position the
>>>>> light correctly to start off with instead of placing it at the origin
>>>>> and then translating it at some later time.
>>>>> Unless I made a mistake.
>>>> Judging from the code, I see no reason why that should make any
>>> Pulled directly from the previous version of this section:
>>> "For point lights and spotlights you could also place the light source
>>> and the looks_like object at the origin and translate them together
>>> later. But for parallel lights this will not work."
>>> Did I get it wrong? Just trying to honor what was previously mentioned!
>> I can't say for sure at the moment. All I can say is that I didn't find
>> anything in the code that would explain that wording, but I might have
>> overlooked something. I guess experiments may be needed.
>> Maybe the sentence was placed there not so much due to unexpected
>> effects on the looks_like object, but unexpected effects on the light
>> source itself. (For instance, whether or wheter not POV-Ray translates
>> the `point_at` location along with the parallel light source, either way
>> the effect may be surprising to some users.)
> I posted a test scene in p.t.s-f.
Oops, I was wrong. But translation is *dangerous*. As per clipka's
response to my post:
> 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.
I.e. translating a light source translates the location of the source of
the light *and* the location the light is pointing at, which could
produce unwanted effects. This should be mentioned in the article. Or at
least state that you should explicitly configure point_at to keep this
You might want to update this page as well:
It recommends translating the light source. Quote:
> It's a good idea to define both things, the light_source and the
> looks_like object, at the origin, and then translate them to their
> right place...
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