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148 Chapter 11: Space Warps and Particle Systems
object surface. The Min value cannot exceed the
Max value, and vice-versa. If you try to raise Min
above Max, or lower Max below Min, both values
change equally.
Density by Material—Varies emission over the
emitter surface based on properties of the material
applied to the emitter. For example, if the object is
assigned a black-and-white checkered diffuse map
and you choose the Grayscale option, particles are
emitted only from the white checks.
Impor tant: For material-influenced emission to appear
properly in the viewports, two conditions are required:
• Atleastoneviewportmustbesettoashadeddisplay
mode.
• The material or map must have Show Map In
Viewpor t turned on in the Material Editor.
The options are as follows:
•
Grayscale—Thesoftwareinternallyconvertsthe
material-based coloring (diffuse) to grayscale,
and then emits more part icles in lighter areas
and fewer in darker areas.
The box emitter is mapped with a gradie nt. With
Position Object set to Density B y Material > G rayscale,
the particles appea r with greater frequency in the lighter
areas o f the box.
• Opa city —Particles are more likely to appear on
opaque areas than on transparent areas.
•
Grayscale & Opacity—Combines the two: More
part icles appear on light, opaque areas than on
dark, transparent areas.
•
Red/Green/Blue—Considers only the specified
color channel. The higher its value at any given
pixel,themorelikelyparticlesaretoappear
there.
Use Sub-Material—When on, uses a sub-material
from the Multi/Sub-Object material assigned to
the emitter to define densit y values.
This option a llows usage of “invisible” materials
for particle placement. If the emitter uses a
Multi/Sub-Object material but its geometry
doesn’t use the ID that corresponds to one of the
sub-materials, the sub-material doesn’t appear.
However,theoperatorcanuseittocalculate
the density of particle placement. The software
assumes the material to be applied to the entire
object surface.
Mtl ID—Specifies the material ID of the
sub-material to be used for particle emission.
Separation—When on, the software attempts to
keep the particles apart by the amount specified in
Distance. The likelihood of successfully separating
particles depends on the number of particles, the
specified distance, and the Attempts Max value.
Distance—Specifies the distance, in system units,
by which the software should try to keep the
particles separ ate. Default=1.0.
Distinct Points Only—Limits emission to a specific
number of points (see Total, below ) on the
specified Location type.
Emission points are st i ll randomized; change the
Uniqueness setting to alter these.