Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 318

AFTER EFFECTS CS3 312
User Guide
About paths
Several features of After Effects, including masks and shapes, rely on the concept of a path. A path consists of
segments and vertices. Segments are the lines or curves that connect vertices. Vertices define where each segment of
a path starts and ends. Some Adobe applications use the terms anchor point and path point to refer to a vertex.
You change the shape of a path by dragging its vertices, the direction handles at the end of each vertex's direction lines
(or tangents), or the path segment itself.
You can draw paths in common geometric shapes—including polygons, ellipses, and stars—with the shape tools, or
you can use the Pen tool to draw an arbitrary path. Paths drawn with the Pen tool are either manual Bezier paths or
RotoBezier paths. The main difference between RotoBezier and manual Bezier paths is that direction lines are calcu-
lated automatically for RotoBezier paths, making them easier and faster to draw.
As a path exits a vertex, the angle and length of that vertex's outgoing direction line determine the path. As the path
approaches the next vertex, the path is less influenced by the previous vertex's direction line and more influenced by
the next vertex's incoming direction line.
A
B C
F
D
E
Components of a path
A. Selected vertex B. Selected vertex C. Unselected vertex D. Curved path segment E. Direction line (tangent) F. Direction handle
Paths can have two kinds of vertices: corner points and smooth points. At a smooth point, path segments are
connected as a smooth curve; the incoming and outgoing direction lines are on the same line. At a corner point, a
path abruptly changes direction; the incoming and outgoing direction lines are on different lines. You can draw a
path using any combination of corner and smooth points. If you draw the wrong kind of point, you can change it
later.
A B C
Points on a path
A. Four corner points B. Four smooth points C. Combination of corner and smooth points
When you move a direction line for a smooth point, the curves on both sides of the point adjust simultaneously. By
contrast, when you move a direction line on a corner point, only the curve on the same side of the point as the
direction line is adjusted.