The Persistence of Vision Raytracer (POV-Ray).

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Attached to Project: POV-Ray
Opened by Samuel T. Benge - 2009-08-07
Last edited by Christoph Lipka - 2012-06-21

FS#46 - area_illuminate in area lights is not taking fade_distance into account

It seems that the new area_illuminate flag for area lights does not take into account fade_power and fade_distance. The illumination falloff is still being calculated from the center of the light_source.

Here’s some relevant code:

  look_at 0
plane{y,0 pigment{rgb 1}}
  area_light x*10, z*1, 8, 8
  fade_power 2 fade_distance 1
Closed by  Christoph Lipka
Thursday, 21 June 2012, 23:12 GMT
Reason for closing:  Fixed
Christoph Lipka commented on Friday, 14 August 2009, 00:59 GMT

Confirmed. (Took the liberty to re-format the original report for beauty.)

Light fading seems indeed to be computed globally for the whole area light, not each individual “sub-lights”. The question is whether we want to change this, as it will of course cost some performance. I doubt whether it makes much of a difference in typical use cases, so I’d advocate to make this optional somehow.

I’m thinking aloud about whether it could be decided automatically depending on parameters such as the light source’s size and distance to the point under test; but then again, this would require some “fuzzy logic” to avoid artifacts at the distance where the “detailed” algorithm kicks in.

Samuel T. Benge commented on Friday, 14 August 2009, 21:21 GMT

Thank you for taking the time to look at this.

I think having each "sub-light" account for distance fading would be a great enhancement for the area_illuminate feature. We could finally model realistic-looking fluorescent lights without having to create a costly array of miniature area_lights. We could also add better-looking fill lights, similar to how I made the indoor aqueduct image in the HOF.

I think light fading for area-illuminating light sources could be off by default, with the option to turn it on via a keyword like so:

area_illuminate fade_on

Something like this would turn on the area_illuminate feature and light fading for it both at once :)

Juha Nieminen commented on Monday, 22 March 2010, 14:27 GMT

I don't see a reason why taking the fading parameters into account for each "sublight" would make the calculations significantly slower. It's more an oversight than anything else.

Thorsten Fröhlich commented on Tuesday, 23 August 2011, 06:41 GMT

What is the status of this?

Christoph Lipka commented on Friday, 02 December 2011, 17:34 GMT

implemented with change #5572.


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