A curve is an open path that has a distinct start and end. These end stops are defined by nodes. A curve with just two nodes is referred to as a line.
The path between nodes is known as a segment and can be straight (A) or arched (B). Complex curves are created from multiple nodes connected by segments (C). Lines and curves generally have a stroke applied.
The type of node controls the connected segments. There are three basic types of node:
When drawing curves, any combination of nodes can be used. Each node also has control handles. These appear when the node is selected. The length and slope of the control handles determine the shape of the segment. A node can be edited at any time.
There are advantages to being able to add multiple curves—for example, if you want to make use of odd-even winding for filling with multiple curves.
A shape is a closed path with no discernible start or end. It is made up of multiple nodes and segments.
You can also easily create geometric shapes using the Shape tools. These have special properties that enable you to quickly create otherwise difficult to draw shapes, such as circles, rectangles and polygons.
Shapes which have been constructed using self-intersecting lines can be filled in two different ways: Alternate or Winding.
The Alternative mode determines whether a segment of the shape will be filled by drawing a ray from that point to infinity in any direction, and counting the number of segments within the given shape that the ray crosses through. If this number is odd, the segment exists in the fill region; if even, the segment is outside the fill region.
The Winding mode determines whether a segment of the shape will be filled by drawing a ray from that point to infinity in any direction, and counting the number of instances in which a segment of the shape crosses the ray. Starting from zero, one count is added each time a segment crosses the ray from left to right and one count is subtracted each time a path segment crosses the ray from right to left, from the perspective of the ray. After the number of crossings has been counted, if the result is zero, then the point is considered to be outside the fill path. Otherwise, it is inside the path.