Graphics Programs Reference
In-Depth Information
to help change the aesthetic of your lighting.
Leave it set to
Black
for normal (uncolored)
shadows.
Shadows in Blender Internal
Blender offers two ways to render shadows: ray trac-
ing and shadow buffers.
This Layer Only
This causes only objects on the
same layer as the lamp to cast shadows, though
objects on any layer may be lit by the lamp as
long as the corresponding option isn't turned
on in the Lamp panel.
Ray Tracing
The first method uses ray tracing to determine the
parts of a mesh in shadow. Ray tracing “fires” rays
out from the camera for each pixel in an image and
draws them to the surface the pixel is facing. Further
rays are drawn to the lights in the scene to determine
whether that point is in light or shadow: If a ray can
be drawn to the light without intersecting another
object, the point is lit; otherwise, it is in shadow.
When there are multiple lights or soft shadows,
multiple rays must be cast per pixel, increasing ren-
der times. The same goes for ray-traced reflections
and transparency, where rays may be reflected or
refracted multiple times. Ray tracing can produce
crisp, pixel-perfect shadows as well as soft shadows,
and it's more accurate but generally slower than
shadow buffers.
Only Shadow
This causes the lamp to cast only
shadows, meaning that you will need other
lights in your scene to light your objects. This
option can be used to create a shadow in a spe-
cific place without affecting the overall look of
your lighting.
Ray-Traced Shadow Options
Enabling Ray Shadow for a lamp gives the following
options:
Samples
This determines the number of samples
taken per pixel for soft shadows in order to
determine the amount of shadowing. Higher
sample numbers give less noisy results. Setting
Samples to 1 gives hard-edged shadows regard-
less of the Soft Size setting.
Shadow Buffers
The other method uses shadow buffers and is
only available for spot lamps. Shadow buffers take
advantage of the spot lamp's restricted cone of
illumination to create a map of which areas are in
shadow over the range of angles that the lamp cov-
ers. Essentially, Blender creates a basic render of
the scene from the lamp's point of view: Areas that
can be seen from the lamp's viewpoint are lit, while
areas that cannot are in shadow.
Shadow-buffer shadows are generally faster to
render than ray-traced ones and are also compatible
with the strand renderer for hair. In fact, the deep
shadow-buffer option for spot lamps is ideally suited
to rendering shadows cast by hair. But getting accu-
rate buffered shadows, which you do by increasing
the resolution of the shadow-buffer map, can use
a lot of memory, and the borders of low-resolution
buffered shadows can look jagged (see Figure 13-2),
so be sure to set them up correctly.
Soft Size
This setting is designed to produce soft
shadows by spreading out the area the light
comes from. The larger the soft size, the softer
and less defined shadows become. Larger sizes
require higher numbers of samples to produce
noise-free results.
Adaptive/Constant QMC
This sets the sampling
method used to determine whether a point on
a surface is in shadow. For
Constant QMC
, the
number of samples taken is always that specified
by the Samples setting. For
Adaptive QMC
, fewer
samples may be taken for areas that are obvi-
ously either in or out of shadow. The
threshold
value dictates the level of certainty required
to determine how many samples are needed:
Higher threshold values are more tolerant and
faster, but they can produce noisier results.
Common Shadow Options
In the Shadow panel of the lamp settings, the fol-
lowing options are common to both ray-traced and
buffer shadows.
Shadow-Buffer Options
Opting for shadow-buffer shadows for spot lamps
gives the following options:
Shadow Color
This option lets you set a color for
the shadow. Of course, in reality, shadows have
no color, so this is actually a trick designed
Buffer Type (Classical/Classic-Halfway/Irregular/
Deep)
The specifics of these types are quite
technical (you can find the details with a bit of
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