In article <3a01b2e0@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   Parallel rays can't create soft shadows. With parallel rays each point
> is hit by exactly 0 or 1 light ray. There's no way a single point could
> be hit by more than 1 light ray when all the rays are parallel to each
> other.

I thought I just finished explaining that I know that, and that I am not 
talking about parallel rays...


>   It's not an alternative since the light rays are not parallel in that
> case. More than 1 ray can hit the same point and thus cause soft shadows.

Um, it *is* an alternative. You can attempt an area light far enough 
that rays of light from each point are nearly parallel but large enough 
to give soft shadows, but which stretches the limits of allowable 
distance, or you can simulate the distance(parallel light!) while 
keeping the soft shadows(area light!) by having a "parallel" area light. 
(notice the quotes!)


>   And besides, there's no difference between an area light located at
> 150 millions of km and 10 km (with equal apparent sizes) when the scene
> is small (some meters wide).

When it is small, the difference certainly is so tiny that it probably 
won't make any difference in the image...but that is often not the case. 
Think of how many sunlit scenes there are that are more than a couple 
meters wide...or more than a couple kilometers in size.
And this sounds like an argument against having *any* parallel light 
patch, not just against "parallel" area lights.


>   "Parallel area light" is a completely wrong term here. If the rays are
> parallel, they all go to the same direction, ie. are all parallel to each
> other, and thus can't cause soft shadows.

I know it is the wrong term, but I don't think there is a better one. 
"Blurred parallel light" isn't quite right...


>   The light rays coming from the Sun are not parallel.

Who said they were?


> : Besides, people will expect having area lights to blur the shadows.
> 
>   Thus, it can't use parallel rays.

I know, as I said, it will have to adjust them slightly to hit a "area 
light" along a line parallel to the light direction.
"Instead of being truely parallel in the area light case, the rays 
should be adjusted so soft shadows still work."
The patch apparently does this already, my question was about why Ron 
thought it was wrong, since doing it the "right" way would make it 
useless except as a way to slow down renders.

And all this still doesn't answer the question that seems to be giving 
Ryan problems...what isn't the parallel light patch doing that he needs? 
What do these "distant lights" do that the parallel light patch doesn't, 
besides render faster?

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

Post a reply to this message