Autodesk LIGHTSCAPE, Manual

Page: 198 / 362

Radiosity Processing 11
190
Lightscape
Make Surface Non-Occluding
The easiest way to alleviate shadow leaks is to ignore
the surface causing the shadow leak. If one surface is
placed directly on another surface, such as a light
switch panel on a wall, you can set the surface on top
to be non-occluding. The light will simply pass
through the surface and will not cast any shadows. In
this kind of situation, the non-occluding approach is
the easiest and most efficient. For more information,
see “Occluding” on page 180.
Light Leaks
Light leaks are the opposite of the shadow leaks
discussed previously. They appear as light extending
into a darker region of a surface.
A typical example of a light leak is one where a single
surface models the floor of two adjacent rooms. If
one room is lit and the other is not, light incident on
the floor of the first room can crawl under the sepa-
rating wall and onto the floor of the second room.
You can prevent light leaks by modeling the floor in
two separate pieces, or you can reduce the leaks by
increasing the mesh subdivision of the floor during
radiosity processing.
F loating Objects
In the following example, the initial sampling mesh
does not fall under the leg of the table because the
surface area is small in relation to the overall area of
the floor. Consequently, the system cannot trigger
adaptive subdivision and completely misses the
shadow of the table leg on the floor. This produces
the visual effect of the table floating over the floor.
The problem is caused by the fact that there is no
original sample point in the floor area shadowed by
the leg of the table that would have triggered an
adaptive subdivision. Setting finer mesh parameters
can correct the situation, as shown in the following
illustration.
In general, it is difficult to avoid this artifact because
it is impractical to make the initial mesh small
enough to guarantee obtaining a sample point inside
every shadow region.
Top: Table leg appears to float above the floor
Bottom: Enlarged view of table
Top: Increased number of
mesh elements corrects
floating effect
Left: Enlarged view of table