Le 16-02-15 05:21, Sven Littkowski a écrit :
> Hi,
>
> I never worked with area light and area illumination before. I tried to
> establish this kind of light based on your example, but I am not sure if
> I gave the correct numbers. And I also don't know the correct order.
>
>
>   #declare MyLight = union
>   {
>    light_source
>    {
>     5000.0*z      // Location
Yes, location of <0, 0, 5000>
>     760.0*x*0.7   // Color?
That makes your light red. It evaluate to rgb <760*0.7, 0, 0>
>     257, 33       // ?
This WILL cause an error and stop parsing.
MUST folloow both area_light AND the two axis
>     area_light    // Type
>   // The POV-Ray docu says vectors and sizes are required for area light
>     < -1000.0, -1300.0, 0.0 > < 1000.0, -1300.0, 5000.0 > 3, 3 // OK?
That can be ok. This define a rectangle set -1300 unit down the y axis, 
and set at an angle.
A 3 by 3 array is extremely croase. Barely ok for a test render. Could 
be used simulate an actual array of 3 by 3 lights if used without jitter 
and adaptive.
>     adaptive 0    //
Good for test render. If good enough, may be kept for final render.
>     area_illumination on //
OK
>    }

You first define the location of the light, then it's colour.
After that, you add the area_light parameters and other light options.

It's as follow, after location and colour/intensity:
area_light
First size of the area light as an axis
Second size of the area light also as an axis
For both axis, the shortcut n*x, n*y and n*z are legal.
Number of samples along the first axis
Number of samples along the second axis

For the axis, it's usualy beter to define them along the reference axis. 
After that, if needed, you can rotate the light as a whole to orient the 
plane as needed. That's much easier than giguring the correct values for 
the axis. Alternatively, it's possible to use some axis manipulation 
macros to calculate the correct values.

It's followed by the other options in any order:

area_illumination will affect the illumination of objects that are close 
to the light's location.

adaptive turn on the adaptive subsampling. The keyword is followed by an 
integer value that set the minimal number of initial subsampling.
A value of 0 will start with only the 4 corners, and if they are not all 
visible or invisible from a given point, then subdivision will occur.
A value of 1 will start with a 3 by 3 array, adaptive 2 will start with 
a 5 by 5 array, subjected to the actual number of sublights in that 
direction.
adaptive allow the use of large number of samples with minimal 
performance hit.

circular moves the sublights inward so that they reside within a circle 
or ellips.
orient will pivot the sublights array so that it's always facing any 
point bein evaluated. It MUST be used with circular and the two axis 
must be ov the same length and the number of samples must be the same in 
both directions.

jitter will randomly move the sublights to reduce banding. If used with 
antialiasing, each antialiasing samples will have a different jittering 
of the sublights.

area_light is compatible with spotlight, cylinder, projected_through, 
parallel.
It's pointless for a shadowless light.

Correctly writing your sample:
light_source{
  Location
  Colour
  area_light // turn on the area_light feature
  5000*z 760*0.7*x //surface covered be the area_light
  257 33 //number of samples along the long and short axis
  jitter // very small effect in this case, help reduce banding
}

This area_light is parallel with the X-Z plane, and it's longest extent 
is alligned along the z axis.
If location is set for 500*y or <0, 500, 0>, the light will be located 
within this square:
<-16.5, 500, -2500> <16.5, 500, 2500>



Alain

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