Using PathIterator to return all line segments that constrain an Area?

Question

In Java, how would one employ PathIterator to iterate through the line segments that constrain an Area? The Area is bound only by lines (but curve support wouldn't hurt).

The method should return a collection of all the line segments.

Burdened

Answer 1

This works (in all situations, I believe), but it might require more thorough testing:

Area area; // The value is set elsewhere in the code    
ArrayList<double[]> areaPoints = new ArrayList<double[]>();
ArrayList<Line2D.Double> areaSegments = new ArrayList<Line2D.Double>();
double[] coords = new double[6];

for (PathIterator pi = area.getPathIterator(null); !pi.isDone(); pi.next()) {
    // The type will be SEG_LINETO, SEG_MOVETO, or SEG_CLOSE
    // Because the Area is composed of straight lines
    int type = pi.currentSegment(coords);
    // We record a double array of {segment type, x coord, y coord}
    double[] pathIteratorCoords = {type, coords[0], coords[1]};
    areaPoints.add(pathIteratorCoords);
}

double[] start = new double[3]; // To record where each polygon starts

for (int i = 0; i < areaPoints.size(); i++) {
    // If we're not on the last point, return a line from this point to the next
    double[] currentElement = areaPoints.get(i);

    // We need a default value in case we've reached the end of the ArrayList
    double[] nextElement = {-1, -1, -1};
    if (i < areaPoints.size() - 1) {
        nextElement = areaPoints.get(i + 1);
    }

    // Make the lines
    if (currentElement[0] == PathIterator.SEG_MOVETO) {
        start = currentElement; // Record where the polygon started to close it later
    } 

    if (nextElement[0] == PathIterator.SEG_LINETO) {
        areaSegments.add(
                new Line2D.Double(
                    currentElement[1], currentElement[2],
                    nextElement[1], nextElement[2]
                )
            );
    } else if (nextElement[0] == PathIterator.SEG_CLOSE) {
        areaSegments.add(
                new Line2D.Double(
                    currentElement[1], currentElement[2],
                    start[1], start[2]
                )
            );
    }
}

// areaSegments now contains all the line segments

Burdened

Thanks for being one of the minority in SO to include comments in your code! – Judicative

This is also tremendously helpful for finding the individual points of the path (either by cycling through the segments and grabbing the first point, or by simplifying the algorithm by skipping the segment generation). – Allysonalma

You could wrap your path iterator in a docs.oracle.com/javase/7/docs/api/java/awt/geom/… to convert your curves to lines, and then use the solution above – Wimberly