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// This file breaks the Ray.hpp <-> AABB.hpp dependency cycle.
#include "AABB.hpp"
#include "Ray.hpp"
// Returns a velocity vectors that avoid collision with `against`, while sliding along it.
// If no collision is detected, returns the original velocity.
// Algorithm is kind of based on "https://www.gamedev.net/tutorials/_/technical/game-programming/swept-aabb-collision-detection-and-response-r3084/",
// but very different (and mine's better :3).
AABB::CollisionResponse AABB::collision_response(Vector<3> v, AABB against) const {
auto origin = center();
Ray ray{origin, v};
auto v_magnitude = v.magnitude();
auto expanded_target = against.sum(*this);
auto raycast = ray.cast(expanded_target, v_magnitude);
if (!raycast.hit) return {v};
// Slide along the collision plane.
auto fulfilled_ratio = (raycast.point - origin).magnitude() / v_magnitude;
auto remaining_ratio = 1.0 - fulfilled_ratio;
auto v_remaining = v * remaining_ratio;
// Project the remaining velocity onto the plane, to which the normal is perpendicular.
auto projected_velocity = v_remaining - v_remaining.project_onto(raycast.normal);
return {
.v_to_collision = raycast.point - origin,
.v_slide = projected_velocity,
.normal = raycast.normal,
};
}
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