Obtain the normalized direction of a ray starting at the center of the coordinate system and going
through the near frustum plane.
<p>
The parameters <code>x</code> and <code>y</code> are used to interpolate the generated ray direction
from the bottom-left to the top-right frustum corners.
@param x
the interpolation factor along the left-to-right frustum planes, within <code>[0..1]</code>
@param y
the interpolation factor along the bottom-to-top frustum planes, within <code>[0..1]</code>
@param dir
will hold the normalized ray direction
@return the <code>dir</code> vector
Obtain the normalized direction of a ray starting at the center of the coordinate system and going through the near frustum plane. <p> The parameters <code>x</code> and <code>y</code> are used to interpolate the generated ray direction from the bottom-left to the top-right frustum corners.
@param x the interpolation factor along the left-to-right frustum planes, within <code>[0..1]</code> @param y the interpolation factor along the bottom-to-top frustum planes, within <code>[0..1]</code> @param dir will hold the normalized ray direction @return the <code>dir</code> vector