Simple collisions for action games (raylib python). Blog post: https://c.har.li/e/2024/03/28/implementing-robust-2D-collision-resolution.html

collision.py

# `pip install raylib` to get pyray
import pyray as rl

from dataclasses import dataclass
import random
from typing import Optional

SIZE = 32

def copy_rect(rect):
    return rl.Rectangle(rect.x, rect.y, rect.width, rect.height)


def get_signed_collision_rec(rect1: rl.Rectangle, rect2: rl.Rectangle) -> rl.Rectangle:
    """Compute the rectangle of intersection between rect1 and rect2.

    If rect2 is to the left or above rect1, the width or height will
    be flipped, respectively."""
    r = rl.get_collision_rec(rect1, rect2)
    if rect2.x < rect1.x:
        r.width = -r.width
    if rect2.y < rect1.y:
        r.height = -r.height
    return r


def resolve_map_collision(map_aabbs, actor_aabb) -> Optional[rl.Vector2]:
    """Fix overlap with map tiles. Returns new position for actor_aabb."""
    # internal copy of actor_aabb that will be mutated
    aabb = copy_rect(actor_aabb)
    if map_aabbs:
        for i in range(10):  # run multiple iters to handle corners/passages
            most_overlap = max(
                (get_signed_collision_rec(r, aabb) for r in map_aabbs),
                key=lambda x: abs(x.width * x.height),
            )
            if abs(most_overlap.width) < abs(most_overlap.height):
                aabb.x += most_overlap.width
            else:
                aabb.y += most_overlap.height

    new_pos = (aabb.x, aabb.y)
    old_pos = (actor_aabb.x, actor_aabb.y)
    return new_pos if new_pos != old_pos else None

@dataclass
class Static:
    rect: rl.Rectangle

@dataclass
class Dynamic:
    rect: rl.Rectangle
    vel: rl.Vector2

    def __hash__(self):
        return id(self)

entities = []

# Oscillations are still a problem (get enough speed, and you can phase through)
entities.append(Static(rl.Rectangle(100 + SIZE, 100 + SIZE, SIZE, SIZE)))
entities.append(Static(rl.Rectangle(100 + SIZE * 3 - 2, 100 + SIZE, SIZE, SIZE)))

rl.init_window(800, 600, "Game")
rl.set_target_fps(60)
while not rl.window_should_close():
    rl.begin_drawing()
    rl.clear_background(rl.BLACK)

    static_rects = [x.rect for x in entities if isinstance(x, Static)]

    p = rl.get_mouse_position()
    p.x = (p.x // SIZE) * SIZE
    p.y = (p.y // SIZE) * SIZE
    width = SIZE
    height = SIZE
    #width = random.uniform(10, 100)
    #height = random.uniform(10, 100)

    if rl.is_mouse_button_released(rl.MOUSE_BUTTON_LEFT):
        entities.append(Static(rl.Rectangle(p.x, p.y, width, height)))
    if rl.is_mouse_button_released(rl.MOUSE_BUTTON_RIGHT):
        entities.append(Dynamic(rl.Rectangle(p.x, p.y, SIZE, SIZE), rl.Vector2(0, 0)))

    prev_pos = {}
    for e in entities:
        if hasattr(e, 'vel'):
            prev_pos[e] = rl.Vector2(e.rect.x, e.rect.y)
            if rl.is_key_down(rl.KEY_LEFT):
                e.vel.x = -2
            elif rl.is_key_down(rl.KEY_RIGHT):
                e.vel.x = 2
            else:
                e.vel.x = 0
            if rl.is_key_down(rl.KEY_UP):
                e.vel.y = -2
            else:
                e.vel.y += 0.1
            e.rect.x += e.vel.x
            e.rect.y += e.vel.y

    for e in entities:
        if isinstance(e, Dynamic):
            if (new_pos := resolve_map_collision(static_rects, e.rect)) is not None:
                e.rect.x, e.rect.y = new_pos

    for e in entities:
        if isinstance(e, Dynamic) and e in prev_pos:
            e.vel.x = e.rect.x - prev_pos[e].x
            e.vel.y = e.rect.y - prev_pos[e].y

    for e in entities:
        if isinstance(e, Static):
            rl.draw_rectangle_rec(e.rect, rl.BROWN)
        elif isinstance(e, Dynamic):
            rl.draw_rectangle_rec(e.rect, rl.GREEN)

    rl.end_drawing()