semi_ellipse.py

import cv2
import numpy as np
from math import sin, cos, pi, sqrt
import random as rand
from time import time


def drawCuttedEllipse(frame, ellipse, cut_coeff, color):
    (cx, cy), (a, b), angle = ellipse
    if a > b:
        a, b = b, a
    a, b = int(a / 2), int(b / 2)
    dx, dy = cx - b, cy - b
    ineq1 = lambda x, y: (x * cos(angle) + y * sin(angle)) ** 2 / b ** 2 \
                         + (x * sin(angle) - y * cos(angle)) ** 2 / a ** 2 <= 1
    ineq2 = lambda x, y: x * cos(angle) + y * sin(angle) <= 2 * b * cut_coeff - b
    h, w, _ = frame.shape
    for y in range(dy, (dy + b * 2) % h):
        for x in range(dx, (dx + b * 2) % w):
            if ineq1(x - cx, y - cy) and ineq2(x - cx, y - cy) and x < w and y < h:
                frame[y, x] = color


def cuttedEllipseContour(ellipse, cut_coeff, resolution=5):
    (cx, cy), (a, b), angle = ellipse
    if a > b:
        a, b = b, a
    a, b = int(a / 2), int(b / 2)
    dx, dy = cx - b, cy - b
    eq1 = lambda x, y: (x * cos(angle) + y * sin(angle)) ** 2 / b ** 2 \
                         + (x * sin(angle) - y * cos(angle)) ** 2 / a ** 2
    ineq2 = lambda x, y: x * cos(angle) + y * sin(angle) <= 2 * b * cut_coeff - b
    acc = []
    for y in range(dy, (dy + b * 2), resolution):
        for x in range(dx, (dx + b * 2)):
            if 0.99 <= eq1(x - cx, y - cy) <= 1.01 and ineq2(x - cx, y - cy):
                acc.append((x, y))
                break
    for y in range(dy, (dy + b * 2), resolution):
        for x in range(dx, (dx + b * 2))[::-1]:
            if 0.99 <= eq1(x - cx, y - cy) <= 1.01 and ineq2(x - cx, y - cy):
                acc.append((x, y))
                break
    return cv2.convexHull(np.array(acc).reshape((-1,1,2)).astype(np.int32))

rot = 0
while True:
    rot += 0.01
    rot %= 2
    angle = rot * pi

    mask = np.full((700, 1000, 3), (0, 0, 0), np.uint8)
    ellipse = (700, 500), (200, 100), angle

    t0 = time()
    ctr1 = cuttedEllipseContour(ellipse, 0.8)
    print(time() - t0)
    cv2.drawContours(mask, [ctr1], -1, (255, 255, 255), -1)

    cv2.imshow('frame', mask)
    if cv2.waitKey(0) & 0xFF == ord('q'):
        break
cv2.waitKey(0)
cv2.destroyAllWindows()