segment_intersects_rectangle_demo.py

from pylab import *

def segment_intersects_rectangle(x1, y1, x2, y2, cx, cy, w, h):
	return (fabs(x1 + x2 - 2.0 * cx) < fabs(x1 - x2) + w and
	        fabs(y1 + y2 - 2.0 * cy) < fabs(y1 - y2) + h and
	        2.0 * fabs((x1 - cx) * (y1 - y2) - (y1 - cy) * (x1 - x2)) < w * fabs(y1 - y2) + h * fabs(x1 - x2))

def test_intersect(plot_line, plot_rect):
	for line in plot_line:
		(x1, x2) = line.get_xdata()
		(y1, y2) = line.get_ydata()
		rx = plot_rect[0].get_xdata()
		ry = plot_rect[0].get_ydata()
		cx = (rx[0] + rx[2]) / 2.0
		cy = (ry[0] + ry[2]) / 2.0
		w = abs(rx[0] - rx[2])
		h = abs(ry[0] - ry[2])
		res = segment_intersects_rectangle(x1, y1, x2, y2, cx, cy, w, h)
		line.set_color("r" if res else "g")

def mouse_move(event):
	if event.xdata is not None and event.ydata is not None:
		rx = plot_rect[0].get_xdata()
		ry = plot_rect[0].get_ydata()
		w2 = abs(rx[0] - rx[2]) / 2.0
		h2 = abs(ry[0] - ry[2]) / 2.0
		plot_rect[0].set_xdata(event.xdata + array([-w2, w2, w2, -w2, -w2]))
		plot_rect[0].set_ydata(event.ydata + array([h2, h2, -h2, -h2, h2]))
		test_intersect(plot_line, plot_rect)
		fig.canvas.draw()

close("all")
fig = figure("Line-Rect test", figsize=(8, 8))
ax = subplot(1, 1, 1)

t = linspace(0, 2 * pi, 81)
px = sin(3 * t)
py = cos(5 * t)

lx = vstack((px[:-1], px[1:]))
ly = vstack((py[:-1], py[1:]))

rx = array([3.2, 4.1, 4.1, 3.2, 3.2])
ry = array([4.3, 4.3, 2.7, 2.7, 4.3])

plot_line = plot(lx, ly, ".-")
plot_rect = plot(rx, ry, ".-", color="b")

test_intersect(plot_line, plot_rect)
fig.canvas.mpl_connect("motion_notify_event", mouse_move)

xlim(-2, 2)
ylim(-2, 2)
tight_layout()
show()