containsPoint method

@override bool containsPoint(Vector2 point)

Returns true if the given point is inside the shape or on the boundary.

Implementation

@override
bool containsPoint(Vector2 point) {
  if (!aabb.intersectsWithVector2(point)) {
    return false;
  }
  final n = _vertices.length;
  if (isConvex) {
    // For a convex polygon, a point is inside if for each edge the cross-
    // product of that edge and a vector from the edge's origin to the point
    // is positive or zero.
    for (var i = 0; i < n; i++) {
      if ((point - _vertices[i]).cross(_edges[i]) < 0) {
        return false;
      }
    }
    return true;
  } else {
    // For a non-convex polygon, we can verify that a point is inside using
    // the winding theorem: if a point is inside, then any ray coming out of
    // that point will intersect the polygon an odd number of times. If the
    // point is outside, the number of intersections will be even.
    // In this case we choose a horizontal ray that starts at `point` and
    // goes towards +∞.
    final x0 = point.x;
    final y0 = point.y;
    var intersectionCount = 0;
    var j = n - 1; // index of previous vertex
    for (var i = 0; i < n; i++) {
      final vi = _vertices[i];
      final vj = _vertices[j];
      if (vi.x == x0 && vi.y == y0) {
        return true;
      }
      if ((vi.y == y0 && vi.x > x0) ||
          (vj.y == y0 && vj.x > x0) ||
          (vi.y > y0) != (vj.y > y0) &&
              ((y0 - vj.y) * (vi.x - vj.x) / (vi.y - vj.y) >= (x0 - vj.x))) {
        intersectionCount++;
      }
      j = i;
    }
    return intersectionCount.isOdd;
  }
}