Script that cuts a line into small pieces

line_cutter.py

import numpy as np
import cv2
import matplotlib.pyplot as plt


def linear_transform(x, src_range=(360, 719), dest_range=(16, 60)):
    src_width, dest_width = src_range[1] - src_range[0], dest_range[1] - dest_range[0]
    return dest_range[1] - (src_range[1] - x) / src_width * dest_width


def norm2(x):
    return np.linalg.norm(x, ord=2)


def cut(start, end, intensity=1, min_y=360):
    xy_delta = np.array([end[0] - start[0], end[1] - start[1]])
    dir_vec = (end - start) / norm2(end - start)
    dest_range = (linear_transform(end[1]), linear_transform(start[1]))
    dest_width = dest_range[1] - dest_range[0]

    moves = []
    cur_pt = start.copy().astype(np.float_)
    centers = np.array([]).reshape(-1, 2)
    centers = np.vstack((centers, cur_pt.reshape(-1, 2)))
    for i in range(25):
        step_pix = (dest_range[1] - norm2(cur_pt - start) / norm2(xy_delta) * dest_width)
        moves.append(step_pix)
        cur_pt += dir_vec * step_pix / intensity
        centers = np.vstack((centers, cur_pt.reshape(-1, 2)))
        if cur_pt[1] <= min_y:
            break

    step_pix = (dest_range[1] - norm2(cur_pt - start) / norm2(xy_delta) * dest_width)
    moves.append(step_pix)

    return centers, moves


def test_cutter():
    start, end = np.array([400, 700]), np.array([640, 360])
    centers, moves = cut(start, end, intensity=1)
    im = np.zeros((720, 1280, 3))
    cv2.line(im, tuple(start), tuple(end), (0, 0, 255), 1)
    for c, m in zip(centers, moves):
        piece = [c[0] - m / 2, c[1] - m / 2, c[0] + m / 2, c[1] + m / 2]
        cv2.rectangle(im, (int(piece[0]), int(piece[1])), (int(piece[2]), int(piece[3])), (0, 255, 0), 1)

    plt.imshow(im, interpolation='bilinear');
    plt.show()