nearest_line_rect_collision.py

import pygame
import math
from pygame import Vector2

pygame.init()

def intersect_line(P0, P1, Q0, Q1):
    d = (P1[0]-P0[0]) * (Q1[1]-Q0[1]) + (P1[1]-P0[1]) * (Q0[0]-Q1[0]) 
    if d == 0:
        return None
    t = ((Q0[0]-P0[0]) * (Q1[1]-Q0[1]) + (Q0[1]-P0[1]) * (Q0[0]-Q1[0])) / d
    u = ((Q0[0]-P0[0]) * (P1[1]-P0[1]) + (Q0[1]-P0[1]) * (P0[0]-P1[0])) / d
    if 0 <= t <= 1 and 0 <= u <= 1:
        return Vector2(round(P1[0] * t + P0[0] * (1-t)), round(P1[1] * t + P0[1] * (1-t)))
    return None

def find_intersect_points_for_rect(start, end, rect):
    intersections = [
        intersect_line(start, end, Vector2(rect.left, rect.top), Vector2(rect.right, rect.top)),
        intersect_line(start, end, Vector2(rect.right, rect.top), Vector2(rect.right, rect.bottom)),
        intersect_line(start, end, Vector2(rect.right, rect.bottom), Vector2(rect.left, rect.bottom)),
        intersect_line(start, end, Vector2(rect.left, rect.bottom), Vector2(rect.left, rect.top))
    ]
    return [i for i in intersections if i]
    

def find_nearest_intersection(start, end, rect):
    intersections = find_intersect_points_for_rect(start, end, rect)
    if not intersections:
        return
    return min(intersections, key=lambda i: start.distance_to(i))

disp = pygame.display.set_mode((320, 320))
pygame.display.set_caption('testing')
clock = pygame.time.Clock()

start = Vector2(20, 170)
angle = math.radians(30)
dist = 100
end = Vector2(start.x + math.cos(angle) * dist, start.y + math.sin(angle) * dist)

view = pygame.Rect(60,60,200,200)

while 1:
    
    for event in pygame.event.get():
        if (event.type == pygame.QUIT or
                (event.type == pygame.KEYDOWN and
                 event.key == pygame.K_ESCAPE)):
            pygame.quit()
            quit()
        
    pressed = pygame.mouse.get_pressed(num_buttons=3)
    if pressed[0]:
        start = Vector2(pygame.mouse.get_pos())
    elif pressed[2]:
        end = Vector2(pygame.mouse.get_pos())
        
            
    disp.fill((30, 20, 30))

    pygame.draw.rect(disp, (100,)*3, view, 1)
        
    pygame.draw.line(disp, (100, 0, 0), start, end)
    
    if intersection := find_nearest_intersection(start, end, view):
        pygame.draw.circle(disp, (0, 200, 0), intersection, 2)
    
    pygame.draw.circle(disp, (0, 200, 200), start, 3)
    pygame.draw.circle(disp, (200, 0, 200), end, 3)
    
    pygame.display.flip()
    
    clock.tick(60)