Drawing a curve is similar to drawing a line, in that a curve is
drawn from the current drawing point to a new point. However, the
curveTo() method adds a third point,
called a control point or handle, to shape the curve. ActionScript
creates curves that use one control point for two points. This trait is
in contrast to many drawing applications, such as Adobe Illustrator,
which uses one or more control points for every point.
Placing the control point is an important part of determining the
shape of your curve. For example, consider turning the line from the section called “12.4 Drawing a Line” into a concave arc, resembling a smile. To
pull the curve down in the middle, you might select a control point
halfway between and below the two end points. Therefore, if the line
spans from (0, 0) to (200, 0), one possible choice for a control point
is (100, 100). These x and y coordinates are passed to the
curveTo() method as the first and second
arguments, while the destination or end point x and y coordinates are
the last two arguments of the method.
var sp:Sprite = new Sprite(); addChild(sp); sp.x = sp.y = 100; var g:Graphics = sp.graphics; g.lineStyle(1, 0x0000FF); g.curveTo(100, 100, 200, 0);
moveTo() in the code
sets the first point at (0, 0), or the sprites registration point. The
final result is a curve that starts at (0, 0), ends at (200, 0), but is
curved through a control point of (100, 100).