"Warp" <war### [at] tagpovrayorg> wrote in message
news:3b837ea4@news.povray.org...
> Ben Chambers <bdc### [at] hotmailcom> wrote:
> : From the
> : documentation, I had understood that area lights had a corner at their
> : location, with the sides of the rectangle going off in the given axes;
>
>   Exactly which part of the documentation gives you this idea?

From the section "Area Lights":

The area_light command defines the size and orientation of the area light as
well as the number of lights in the light source array. The vectors <Axis_1>
and <Axis_2> specify the lengths and directions of the edges of the light.
Since the area lights are rectangular in shape these vectors should be
perpendicular to each other. The larger the size of the light the thicker
the soft part of shadows will be. The integers Size_1 and Size_2 specify the
number of rows and columns of point sources of the. The more lights you use
the smoother your shadows will be but the longer they will take to render.

Specifically, the part about the vectors specifying the lengths of the edges
of the light.  For example, if we have a point P and two vectors U and V, I
would expect the four corners to be
P,   P+U
P+V, P+U+V

Thus, two sides would have a length of |U| and two sides would have a length
of |V|.
However, experimentation shows that the four corners are actually
P-U-V, P+U-V
P-U+V, P+U+V
With the center of the rectangle (more or less :) being located at P.

And so, two sides would have a length of 2*|U| and the other two would have
2*|V|.
Is this the way POV is supposed to behave?  Personally, I like it better (it
makes it easier to position area lights) but it was not what I expected.

...Chambers

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