QuickTime 4 Reference

Shape Geometry

For a path, the shape type does not contain all the geometric information necessary to define the shape. The geometries of paths contain (x, y) coordinate pairs called geometric points --points that specify the location, dimension, and form of the paths:

Curve shapes store three geometric points in their geometry--one to specify where the curve starts, another to specify where the curve ends, and another, called the off-curve control point, to specify the tangents used to define the curve.
A path geometry can also contain multiple contours, but each path contour can contain curves as well as straight lines.

There are two possible views of a geometry: as a list of x, y coordinate pairs and as geometric points plotted on a geometric grid. This second way of viewing geometries is used frequently throughout this chapter, as it shows not only the geometric points, but also the implied edges that connect them. Typically, the figures in this chapter do not show the grid, but just the points and edges.

Each geometric point in a geometry has a geometry index --if you consider the geometry as a list of geometric points starting from the first geometric point of the first contour to the last geometric point of the last contour, the geometry index of a particular geometric point is its position in this list.

QuickDraw GX takes into consideration the direction that an edge is pointing in a number of circumstances:

When filling a shape. QuickDraw GX allows you to choose how a shape should be filled. The next section, "Shape Fill," discusses how the direction of an edge can affect how QuickDraw GX fills a shape.
When determining the contour direction of a contour.
When determining the inside or outside of a contour. QuickDraw GX normally defines the right side of an edge to be the inside and the left side to be the outside.