is defined by the vector from <tex2html_verbatim_mark>#math70#<tex2html_image_mark>#tex2html_wrap_inline4701#⇧ to <tex2html_verbatim_mark>#math71#<tex2html_image_mark>#tex2html_wrap_inline4703#⇧. Along
this axis a total of <#325#><EM>usamp</EM><#325#> samples will be taken.
The <I>v</I> axis of the light source is defined by the vector
from <tex2html_verbatim_mark>#math72#<tex2html_image_mark>#tex2html_wrap_inline4706#⇧ to <tex2html_verbatim_mark>#math73#<tex2html_image_mark>#tex2html_wrap_inline4708#⇧. Along this axis a total of
<#328#><EM>vsamp</EM><#328#> samples will be taken.
</DD>
</DL>The values of <#330#><EM>usamp</EM><#330#> and <#331#><EM>vsamp</EM><#331#> are usually chosen to be
proportional to the lengths of the <I>u</I> and <I>v</I> axes. Choosing a
relatively high number of samples will result in a good approximation
to a ``real'' quadrilateral source. However, because complete
lighting calculations are performed for each sample,
the computational cost is directly proportional to the product
of <#332#><EM>usamp</EM><#332#> and <#333#><EM>vsamp</EM><#333#>.