Crafter.Debug/examples/Basic/interfaces/Basic.World.cppm

// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

// Balls dropped onto a floor slab, in two dimensions, at a fixed step. y is
// up, in metres; the slab's top is at floor.top and it is floor.thickness
// thick.
export module Basic.World;
import std;

export namespace Basic {
    struct Ball {
        std::int32_t id = 0;
        float x = 0;
        float y = 0;
        float vx = 0;
        float vy = 0;
        float radius = 0.1f;
        // Below the floor, and so out of the scene for good.
        bool lost = false;
    };

    struct Physics {
        float gravity = -9.81f;
        // The share of its speed a ball keeps when it bounces.
        float restitution = 0.6f;
        // Collision checks per tick.
        std::int32_t substeps = 1;
    };

    struct Floor {
        float top = 0;
        float thickness = 0.1f;
    };

    // What `wait --event Bounce` waits for, sent for bounces faster than 1 m/s.
    struct BounceEvent {
        std::int32_t ball = 0;
        float speed = 0;
    };

    class World {
    public:
        Physics physics;
        Floor floor;

        // Removes every ball and drops the scene's five, as balls 1 to 5.
        void Reset();
        // Removes every ball; ids start again from 1.
        void Clear();
        // Returns the new ball's id.
        std::int32_t Spawn(float x, float y, float vy, float radius);
        void Tick(float dt);

        const std::deque<Ball>& Balls() const { return balls; }
        const Ball* Find(std::int32_t id) const;
        double Time() const { return time; }
        std::int32_t Lost() const;
        // The fastest ball's speed in the last tick, in m/s.
        float Fastest() const { return fastest; }

    private:
        std::deque<Ball> balls;
        std::int32_t nextId = 1;
        double time = 0;
        float fastest = 0;
    };
}