5

Size: This slider becomes available when Rectangle or Box is chosen in the Shape pop-up
menu. Defines the size of the rectangle or cube from which particles are emitted. The
Size slider is available whether the Arrangement is set to Outline, Tile Fill, or Random Fill.
When Rectangle is the selected shape, the Width and Height parameters become available.
When Box is selected, an additional Depth parameter is available.
Note: The Height is measured in project pixels; however, the Width is measured in square
pixels. This is done so a shape that is numerically square will look square when Correct
for Aspect Ratio is turned on (checkmarked) in the View pop-up menu in the top-right
corner of the Canvas.
Columns: This slider becomes available when one of the following is chosen in the Shape
pop-up menu: Rectangle, Circle, Image, Box, or Sphere; in addition, Arrangement must
be set to Tile Fill. This parameter specifies the number of horizontal emitter points on a
grid over the selected emitter shape. In the case of an irregular shape (nonrectangular),
grid points that fall outside of the shape are ignored.
Rows: This slider becomes available when one of the following is chosen in the Shape
pop-up menu: Rectangle, Circle, Image, Box, or Sphere; in addition, Arrangement must
be set to Tile Fill. This parameter specifies the number of vertical emitter points on a grid
over the selected emitter shape. In the case of an irregular shape (nonrectangular), grid
points that fall outside of the shape are ignored.
Ranks: This slider becomes available when Box or Sphere is chosen in the Shape pop-up
menu and Tile Fill is the selected Arrangement. This parameter specifies the number of
points in Z space on a grid over the selected shape from which particles are emitted.
Tile Offset: This slider becomes available when one of the following is chosen in the
Shape pop-up menu: Rectangle, Circle, Image, Box, or Sphere; in addition, Arrangement
must be set to Tile Fill. Values from 0 to 100% offset the rows toward the right, and values
from 0 to –100% offset the rows toward the left. A value of 50 or –50% creates a
“brickwork” pattern.
Image Source: This image well, available when Image is chosen in the Shape pop-up
menu, lets you specify the object used to define the shape of the emitter.
Shape Source: This image well, available when Shape is set to Geometry, lets you specify
a spline object to define the shape of the emitter.
Emission Alpha Cutoff: This slider becomes available when Image is chosen in the Shape
pop-up menu. When the Image Source object contains an alpha channel, this slider
defines the minimum opacity value necessary to create particles at that point on the
source image. For example, when set to 25%, particles appear only where the alpha value
of the image is equal to or greater than 25% opacity. The lower the Emission Alpha Cutoff
value, the more particles appear. For this parameter to be effective, the alpha channel
must have areas of varying transparency.
701Chapter 14 Working with Particles