finding where a ray intersects the edge of a bounding rectangle

gistfile1.py

import sys
from math import pi, tan
import pygame as pg
from angles import get_angle, project


def get_edge_pos(origin, angle, rect):
    """Returns the intersection of the ray from
        origin at angle with the edge of rect. origin
        should be a point inside rect."""
    tl = get_angle(origin, rect.topleft)
    tr = get_angle(origin, rect.topright)
    br = get_angle(origin, rect.bottomright)
    bl = get_angle(origin, rect.bottomleft)

    if tl >= angle >= tr:
        edge_dist = origin[1] - rect.top
        edge_angle = get_angle(origin, (origin[0], rect.top))
        dist = edge_dist * tan(angle - edge_angle)
        edge_pos = (origin[0] - dist, rect.top)
        
    elif (tr >= angle>= 0)  or (2*pi >= angle>= br):
        edge_dist = rect.right - origin[0]
        edge_angle = get_angle(origin, (rect.right, origin[1]))
        dist = edge_dist * tan(angle - edge_angle)
        edge_pos = (rect.right, origin[1] - dist)
    elif bl <= angle<= br:
        edge_dist = rect.bottom - origin[1]
        edge_angle = get_angle(origin, (origin[0], rect.bottom))
        dist = edge_dist * tan(angle - edge_angle)
        edge_pos = (origin[0] + dist, rect.bottom)
    elif tr <= angle<= br:
        edge_dist = origin[0] - rect.left
        edge_angle = get_angle(origin, (rect.left, origin[1]))
        dist = edge_dist * tan(angle- edge_angle)
        edge_pos = (rect.left, origin[1] + dist)
    return edge_pos


class AngleTest(object):
    def __init__(self):
        self.done = False
        self.screen = pg.display.set_mode((800, 800))
        self.screen_rect = self.screen.get_rect()
        self.clock = pg.time.Clock()
        self.origin = self.screen_rect.center
        #self.origin = (200, 200)
        #self.origin = (600, 200)
        #self.origin = (600, 600)
        #self.origin = (200, 600)
        
    def event_loop(self):
        for event in pg.event.get():
            if event.type == pg.QUIT:
                self.done = True
                
    def update(self):
        self.mouse_pos = pg.mouse.get_pos()
        self.ray_end = get_edge_pos(self.origin, 
                                    get_angle(self.origin, self.mouse_pos),
                                    self.screen_rect)
        
    def draw(self):        
        self.screen.fill(pg.Color("black"))
        pg.draw.line(self.screen, pg.Color("green"), self.origin, self.ray_end)
        pg.draw.line(self.screen, pg.Color("red"), self.origin, self.mouse_pos)
        
    def run(self):
        while not self.done:
            self.event_loop()
            self.update()
            self.draw()
            pg.display.update()
            self.clock.tick(60)
        
if __name__ == "__main__":
    test =AngleTest()
    test.run()
    pg.quit()
    sys.exit()