Function segment_hits

lib/matplotlib/lines.py:98–132

Return the indices of the segments in the polyline with coordinates (*cx*, *cy*) that are within a distance *radius* of the point (*x*, *y*).

(cx, cy, x, y, radius)

def segment_hits(cx, cy, x, y, radius):
    """
    Return the indices of the segments in the polyline with coordinates (*cx*,
    *cy*) that are within a distance *radius* of the point (*x*, *y*).
    """
    # Process single points specially
    if len(x) <= 1:
        res, = np.nonzero((cx - x) ** 2 + (cy - y) ** 2 <= radius ** 2)
        return res

    # We need to lop the last element off a lot.
    xr, yr = x[:-1], y[:-1]

    # Only look at line segments whose nearest point to C on the line
    # lies within the segment.
    dx, dy = x[1:] - xr, y[1:] - yr
    Lnorm_sq = dx ** 2 + dy ** 2  # Possibly want to eliminate Lnorm==0
    u = ((cx - xr) * dx + (cy - yr) * dy) / Lnorm_sq
    candidates = (u >= 0) & (u <= 1)

    # Note that there is a little area near one side of each point
    # which will be near neither segment, and another which will
    # be near both, depending on the angle of the lines.  The
    # following radius test eliminates these ambiguities.
    point_hits = (cx - x) ** 2 + (cy - y) ** 2 <= radius ** 2
    candidates = candidates & ~(point_hits[:-1] | point_hits[1:])

    # For those candidates which remain, determine how far they lie away
    # from the line.
    px, py = xr + u * dx, yr + u * dy
    line_hits = (cx - px) ** 2 + (cy - py) ** 2 <= radius ** 2
    line_hits = line_hits & candidates
    points, = point_hits.ravel().nonzero()
    lines, = line_hits.ravel().nonzero()
    return np.concatenate((points, lines))


def _mark_every_path(markevery, tpath, affine, ax):