QuickTime 4 Reference

Creating and Drawing Paths

A path contour is a series of connected points. The contour can contain both straight lines and curves. Therefore, the geometric points that make up a path contour can be on-curve points or off-curve control points. QuickDraw GX defines the gxPath structure to encapsulate a path contour geometry:



 
struct gxPath {

    long                vectors;

    long                controlBits[gxAnyNumber];

    struct gxPoint      vector[gxAnyNumber];

};

The vectors field indicates the number of geometric points in the path and the vector array contains the geometric points themselves. The controlBits array specifies which geometric points are on-curve points and which are off-curve control points. A value of 0 indicates an on-curve point and a value of 1 indicates an off-curve point. For example, a controlBits field with the value



 
0x55555555   /* 0101 0101 0101 0101 ... */

indicates that every other point is an off-curve control point; the first point is on curve, the second point is off, and so on. As another example, a controlBits field value of



 
0x00000000   /* 0000 0000 0000 0000 ... */

indicates all points are on curve, which effectively creates a polygon.

Notice that the controlBits array allows you to specify sequential off-curve control points. For example, a controlBits value of



 
0xFFFFFFFF   /* 1111 1111 1111 1111 ... */

indicates that all points are off curve. When you indicate that two control points in a row are off curve, QuickDraw GX assumes an on-curve point midway between them.

The path shape allows you to group any number of contours within a single QuickDraw GX shape. The gxPaths structure encapsulates the multiple-path geometry:



 
struct gxPaths {

    long             contours;

    struct gxPath    contour[gxAnyNumber];

};

The contours field indicates the total number of contours (in other words, the total number of separate paths), and the contour array contains the path geometries.

Creating and Drawing Paths

Creating Paths With a Single Contour

Creating Paths Using Only Off-Curve Points

Creating Paths With Multiple Contours