使用 PathIterator 返回限制区域的所有线段? [英] Using PathIterator to return all line segments that constrain an Area?

问题描述

在 Java 中，如何使用 PathIterator 遍历约束 区域?Area 仅由线约束(但曲线支持不会受到影响).

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).

该方法应该返回所有线段的集合.

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

推荐答案

这有效(我相信在所有情况下)，但它可能需要更彻底的测试:

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

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