Adobe After Effects CS4 - Manual (Page 342)

336 USING AFTER EFFECTS CS4
Drawing, painting, and paths
Last updated 12/21/2009
Projecting Cap The stroke extends beyond the end of the path for a number of pixels equal to the stroke width in
pixels. The end is squared off.
Line Join options for strokes
The Line Join property for a stroke determines the appearance of the stroke where the path suddenly changes direction
(turns a corner).
Miter Join A pointed connection. The Miter Limit value determines the conditions under which a beveled join is used
instead of a miter join. If the miter limit is 4, then when the length of the point reaches four times the stroke weight, a
bevel join is used instead. A miter limit of 1 causes a bevel join.
Round Join A rounded connection.
Bevel Join A squared-off connection.
Fill rules for shapes
A fill operation works by painting color in the area defined as inside a path. Determining what is considered inside a
path is easy when the path is something simple, like a circle. However, when a path intersects itself, or when a
compound path consists of paths enclosed by other paths, determining what is considered inside is not as easy.
After Effects uses one of two rules to determine what is considered inside a path for the purpose of creating fills. Both
rules count the number of times that a straight line drawn from a point crosses the path on its way out of the area
surrounded by a path. The nonzero winding fill rule considers path direction; the even-odd fill rule does not.
After Effects and Illustrator use the nonzero winding fill rule as the default.
Self-intersecting path with Fill Rule set to Non-Zero Winding Fill Rule (left) compared with Even-Odd Fill Rule (right)
Even-odd fill rule If a line drawn from a point in any direction crosses the path an odd number of times, then the point
is inside; otherwise, the point is outside.
Nonzero winding fill rule The crossing count for a line is the total number of times that the line crosses a left-to-right
portion of the path minus the total number of times that the line crosses a right-to-left portion of the path. If a line
drawn in any direction from the point has a crossing count of zero, then the point is outside; otherwise, the point is
inside.
A more intuitive way to think of the nonzero winding rule is to think of a path as a loop of string. A point is considered
outside the path if you can put your finger at that point and then pull the string away without it being caught, wrapped
around your finger.
Because the nonzero winding fill rule takes path direction into account, using this fill rule and reversing the direction
of one or more paths in a compound path is useful for creating holes in compound paths.
To reverse the direction of a path, click the Reverse Path Direction On button for the path in the Timeline panel.