2009

about -1%, respectively, and values of 129 to 255 result in multipliers of
about 1% to 100%, respectively.
■ RGB as World XYZ Mult. Works like Grayscale Multiplier, but uses the
intensity of the material's red, green, and blue channels to affect particle
speed on the world X, Y, and Z axes, respectively. So, for example, if the
material pixel is pure red, that is, its RGB value is (255,0,0), then the particle
will retain its current speed on the world X axis, but its speed on the Y and
Z axes will be reduced to 0. Similarly, a medium-yellow pixel (128,128,0)
will cause speed on the world X and Y axes to be reduced by half, and will
cut speed on the Z axis to 0.
■ RGB as Local XYZ Mult. Works like RGB as World XYZ Mult., but uses
the object's local coordinates rather than world coordinates.
Use Sub-Material When on, uses a sub-material from the Multi/Sub-Object
material assigned to the Surface Geometry object to define speed.
This option allows usage of “invisible” materials for controlling particle speed.
If the emitter uses a Multi/Sub-Object material but its geometry doesn't use
the ID that corresponds one of the sub-materials, the sub-material doesn't
appear. However, the operator can use it to calculate 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
speed control.
Direction group
The Direction drop-down list lets you specify which way the particles go after
they're born. Default=Surface Normals. In most cases, the actual direction also
depends on the icon orientation. The primary exception is when Position >
Location is set to Pivot.
Particle movement is always in a straight line unless influenced by other
factors.
Surface Normals Each particle moves along a line perpendicular to the nearest
face. The direction the surface faces doesn't matter.
Out Of Surface Particles move away from the closest face.
2892 | Chapter 14 Space Warps and Particle Systems