Crafter.Debug/examples/Basic/implementations/Basic.World.cpp

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

module Basic.World;
import std;
import Basic.DebugShim;
namespace Debug = Crafter::Debug;

void Basic::World::Reset() {
    Clear();
    constexpr std::array<float, 5> heights = { 1, 3, 8, 20, 60 };
    for (std::size_t i = 0; i < heights.size(); ++i) {
        Spawn(static_cast<float>(i) - 2.0f, heights[i], 0, 0.1f);
    }
}

void Basic::World::Clear() {
    balls.clear();
    time = 0;
    fastest = 0;
}

std::int32_t Basic::World::Spawn(float x, float y, float vy, float radius) {
    const std::int32_t id = nextId++;
    balls.push_back({ .id = id, .x = x, .y = y, .vy = vy, .radius = radius });
    Debug::Log("world", "ball {} dropped from {:.1f} m", id, y);
    return id;
}

void Basic::World::Tick(float dt) {
    const std::int32_t steps = std::max(1, physics.substeps);
    const float h = dt / static_cast<float>(steps);
    const float bottom = floor.top - floor.thickness;
    fastest = 0;
    for (Ball& ball : balls) {
        for (std::int32_t step = 0; step < steps; ++step) {
            ball.vy += physics.gravity * h;
            ball.x += ball.vx * h;
            ball.y += ball.vy * h;
            if (ball.lost) continue;
            // A falling ball that overlaps the slab bounces off its top.
            if (ball.vy < 0 && ball.y - ball.radius < floor.top && ball.y + ball.radius > bottom) {
                const float speed = -ball.vy;
                ball.y = floor.top + ball.radius;
                ball.vy = speed * physics.restitution;
                if (speed > 1) Debug::Emit("Bounce", BounceEvent{ .ball = ball.id, .speed = speed });
            }
        }
        if (!ball.lost && !Debug::Check(ball.y + ball.radius >= bottom, "physics", "ball {} is below the floor: y {:.2f} m, vy {:.1f} m/s", ball.id, ball.y, ball.vy)) {
            ball.lost = true;
        }
        fastest = std::max(fastest, std::hypot(ball.vx, ball.vy));
    }
    Debug::Sample("solver.fastest", fastest);
    time += dt;
}

const Basic::Ball* Basic::World::Find(std::int32_t id) const {
    const auto found = std::ranges::find(balls, id, &Ball::id);
    return found == balls.end() ? nullptr : &*found;
}

std::int32_t Basic::World::Lost() const {
    return static_cast<std::int32_t>(std::ranges::count(balls, true, &Ball::lost));
}