Function paths

plotter/contour.go:345–392

paths extends a conrecLine function to build a set of contours that represent paths along contour lines. It is used as the engine for a closure where ends and conts are closed around in a conrecLine function, and l and z are the line and height values provided by conrec. At the end of a conrec call,

(l line, z float64, ends map[float64]endMap, conts contourSet)

// line and height values provided by conrec. At the end of a conrec call,
// conts will contain a map keyed on the set of paths.
func paths(l line, z float64, ends map[float64]endMap, conts contourSet) {
	zEnds, ok := ends[z]
	if !ok {
		zEnds = make(endMap)
		ends[z] = zEnds
		c := newContour(l, z)
		zEnds[l.p1] = c
		zEnds[l.p2] = c
		conts[c] = struct{}{}
		return
	}

	c1, ok1 := zEnds[l.p1]
	c2, ok2 := zEnds[l.p2]

	// New segment.
	if !ok1 && !ok2 {
		c := newContour(l, z)
		zEnds[l.p1] = c
		zEnds[l.p2] = c
		conts[c] = struct{}{}
		return
	}

	if ok1 {
		// Add l.p2 to end of l.p1's contour.
		if !c1.extend(l, zEnds) {
			panic("internal link")
		}
	} else if ok2 {
		// Add l.p1 to end of l.p2's contour.
		if !c2.extend(l, zEnds) {
			panic("internal link")
		}
	}

	if c1 == c2 {
		return
	}

	// Join conts.
	if ok1 && ok2 {
		if !c1.connect(c2, zEnds) {
			panic("internal link")
		}
		delete(conts, c2)
	}
}

// path is a set of points forming a path.
type path []point