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main_old.cpp
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main_old.cpp
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#include <cstdio>
#include <cassert>
#include <cstdlib>
#include <cstdint>
#include <cstddef>
#include <cmath>
#include <charconv>
#include <vector>
#include <string>
#include <unordered_map>
#include <memory>
#include <bitset>
#include <span>
#include <optional>
#include <fmt/core.h>
#include <SDL2/SDL.h>
#include "cmdline.hpp"
/* typedefs and constants */
using u8 = uint8_t;
using u16 = uint16_t;
using u32 = uint32_t;
using u64 = uint64_t;
using i8 = int8_t;
using i16 = int16_t;
using i32 = int32_t;
using i64 = int64_t;
const int NUM_PARTICLES = 10;
const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT = 600;
const int PARTICLE_SIZE = 32;
const float PARTICLE_MIN_VEL = 0.001f;
const float PARTICLE_MAX_VEL = 0.5f;
// use for game loop 4 (the one actually in use)
// all these constants are in milliseconds (ms)
// this is due to SDL using ms too
const i32 MIN_FRAME_TIME = 3;
const float ELAPSED_MAX = 1000.0f/30.0f;
const float TICK_DURATION = 1000.0f/60.0f;
// used by other game loops
const int TICK_INTERVAL = 30;
/* vector class */
template <typename T, unsigned Dim> struct VecData;
#define VECDATA(dim, ...) \
template <typename T> struct VecData<T, dim> { \
union { \
T d[2]; \
struct { __VA_ARGS__ }; \
}; \
\
constexpr VecData(auto... args) : d(args...) {} \
};
VECDATA(2, T x; T y;)
VECDATA(3, T x; T y; T z;)
#undef VECDATA
template <typename T, unsigned Dim>
struct Vec : VecData<T, Dim> {
constexpr Vec() = default;
constexpr Vec(auto... args) : VecData<T, Dim>(args...) {}
constexpr const T & operator[](std::size_t pos) const { return this->d[pos]; }
constexpr T & operator[](std::size_t pos) { return this->d[pos]; }
constexpr T *data() { return this->d; }
constexpr const T *data() const { return this->d; }
constexpr std::size_t size() const { return Dim; }
constexpr T *begin() { return this->d; }
constexpr T *end() { return this->d + Dim; }
constexpr const T *begin() const { return this->d; }
constexpr const T *end() const { return this->d + Dim; }
constexpr T length_squared() const
{
T res = 0;
for (auto i = 0u; i < Dim; i++)
res += this->d[i] * this->d[i];
return res;
}
constexpr T length() const
{
if constexpr(std::is_same_v<T, float>) return sqrtf(length_squared());
return std::sqrt(length_squared());
}
Vec<T, Dim> unit() { return *this / length(); }
#define VEC_OP(op) \
constexpr Vec<T, Dim> & operator op(const Vec<T, Dim> &v) \
{ \
for (auto i = 0u; i < Dim; i++) \
this->d[i] op v.d[i]; \
return *this; \
}
VEC_OP(+=) VEC_OP(-=) VEC_OP(%=)
#undef VEC_OP
};
#define VEC_OP(op) \
template <typename T, unsigned Dim> \
constexpr Vec<T, Dim> operator op(const Vec<T, Dim> &v, T scalar) \
{ \
Vec<T, Dim> res; \
for (auto i = 0u; i < Dim; i++) \
res[i] = v[i] op scalar; \
return res; \
}
VEC_OP(+) VEC_OP(-) VEC_OP(*) VEC_OP(/)
#undef VEC_OP
#define VEC_OP(op) \
template <typename T, unsigned Dim> \
constexpr Vec<T, Dim> operator op(const Vec<T, Dim> &v1, const Vec<T, Dim> &v2) \
{ \
Vec<T, Dim> res; \
for (auto i = 0u; i < Dim; i++) \
res[i] = v1[i] op v2[i]; \
return res; \
}
VEC_OP(+) VEC_OP(-)
#undef VEC_OP
template <typename T, unsigned Dim>
T vec_dot(Vec<T, Dim> a, Vec<T, Dim> b)
{
float res = 0.0f;
for (auto i = 0u; i < Dim; i++)
res += a[i] * b[i];
return res;
}
template <typename T, unsigned Dim>
Vec<T, Dim> vec_lerp(Vec<T, Dim> a, Vec<T, Dim> b, float t)
{
Vec<T, Dim> res;
for (auto i = 0u; i < Dim; i++)
res[i] = std::lerp(a[i], b[i], t);
return res;
}
template <typename T, unsigned Dim>
auto vec_cross(Vec<T, Dim> a, Vec<T, Dim> b)
{
if constexpr(Dim == 2) { return a[0]*b[1] - a[1]*b[0]; }
if constexpr(Dim == 3) { return Vec<T, Dim>{ a[1]*b[2] - a[2]*b[1],
a[2]*b[0] - a[0]*b[2],
a[0]*b[1] - a[1]*b[0] }; }
return Vec<T, Dim>{};
}
using vec2 = Vec<float, 2>;
/* geometry */
struct Rect {
vec2 pos;
vec2 size;
Rect() = default;
Rect(vec2 p, vec2 s) : pos{p}, size{s} { }
Rect(float x, float y, float w, float h) : pos{x, y}, size{w, h} { }
SDL_Rect to_sdl() { return (SDL_Rect) { int(pos.x), int(pos.y), int(size.x), int(size.y) }; }
};
struct Circle {
vec2 center;
float radius;
Circle() = default;
Circle(vec2 c, float r) : center{c}, radius{r} { }
Circle(float x, float y, float r) : center{x, y}, radius{r} { }
vec2 top_left() const { return center - radius; }
vec2 bottom_right() const { return center + radius; }
vec2 left() const { return vec2{center.x - radius, center.y}; }
vec2 right() const { return vec2{center.x + radius, center.y}; }
vec2 up() const { return vec2{center.x, center.y - radius}; }
vec2 down() const { return vec2{center.x, center.y + radius}; }
};
bool circle_point_intersecting(Circle c, vec2 p)
{
return (c.center - p).length_squared() <= c.radius;
}
bool circle_circle_intersecting(Circle c1, Circle c2)
{
return (c1.center - c2.center).length_squared() <= powf(c1.radius + c2.radius, 2);
}
bool rect_point_intersecting(Rect r, vec2 p)
{
return p.x > r.pos.x && p.x < r.pos.x + r.size.x
&& p.y > r.pos.y && p.y < r.pos.y + r.size.y;
}
bool rect_rect_intersecting(Rect r1, Rect r2)
{
return r1.pos.x < r2.pos.x + r2.size.x
&& r2.pos.x < r1.pos.x + r1.size.x
&& r1.pos.y < r2.pos.y + r2.size.y
&& r2.pos.y < r1.pos.y + r1.size.y;
}
/* rng */
// returns a float between 0 and 1
float random_unit()
{
return float(rand()) / (u64(RAND_MAX) + 1);
}
float random_between(float min, float max)
{
assert(max - min > 0);
return std::lerp(min, max, random_unit());
}
// (m, n]
int random_integer_between(int m, int n)
{
assert(n - m > 0);
return (rand() % int(n - m)) + m;
}
bool random_bool()
{
return rand() % 2;
}
float random_no_zero(float min, float max)
{
float nums[2];
nums[0] = random_between(-max, 0);
nums[1] = random_between(min, max);
int which = int(random_bool());
return nums[which];
}
/* collision */
std::optional<float> ccd_circle_line(float p0, float p1, float r, float b)
{
float tc1 = (b + r - p0) / (p1 - p0);
float tc2 = (b - r - p0) / (p1 - p0);
float tc = std::min(tc1, tc2);
if (tc < 0.0f || tc > 1.0f)
return std::nullopt;
float pc = std::lerp(p0, p1, tc);
return pc*2 - p1;
}
float pow2f(float n) { return n*n; }
std::pair<vec2, vec2> elastic_collision_2d(vec2 v1, vec2 v2, float m1, float m2, vec2 c1, vec2 c2)
{
auto f = [](vec2 v1, vec2 v2, float m1, float m2, vec2 c1, vec2 c2) {
return v1 - (c1 - c2) * (2.0f * m2 / (m1 + m2)) * vec_dot(v1 - v2, c1 - c2) / pow2f((c1 - c2).length());
};
vec2 v1p = f(v1, v2, m1, m2, c1, c2);
vec2 v2p = f(v2, v1, m2, m1, c2, c1);
return std::make_pair(v1p, v2p);
}
/* particle and engine classes */
struct Graphics {
SDL_Texture *tex;
vec2 size;
};
struct {
std::vector<Graphics> loaded_gfx;
int add(Graphics &&gfx)
{
loaded_gfx.emplace_back(gfx);
return loaded_gfx.size() - 1;
}
Graphics & operator[](int id) { return loaded_gfx[id]; }
vec2 gfx_size(int id) { return loaded_gfx[id].size; }
} gfx_handler;
struct Particle {
Circle hitbox;
vec2 vel = {0,0};
vec2 accel = {0,0};
int gfx_id; // which Graphics to use
float mass = 1.0f;
int frame = 0;
Particle(vec2 p, float r, vec2 v, int id, int f)
: hitbox{p, r}, vel{v}, gfx_id{id}, frame{f}
{ }
void update(float dt);
vec2 adjust_pos(vec2 p0, vec2 p1, float r);
const vec2 & pos() const { return hitbox.center; }
};
std::pair<vec2, vec2> particle_collision(const Particle &p, const Particle &q)
{
return elastic_collision_2d(p.vel, q.vel, p.mass, q.mass, p.hitbox.center, q.hitbox.center);
}
struct Engine {
SDL_Window *window;
SDL_Renderer *rd;
std::vector<Particle> particles;
int wnd_width = SCREEN_WIDTH, wnd_height = SCREEN_HEIGHT;
void init(int width, int height);
void deinit();
bool poll();
void draw_one(float dt, vec2 pos, vec2 vel, int gfx_id, int frame);
void draw(float dt);
int load_gfx(std::string_view pathname);
void tick(float dt);
void add_sprite(Particle particle);
void draw_uniform_grid_lines(int grid_size);
int screen_width() const { return wnd_width; }
int screen_height() const { return wnd_height; }
} engine;
/* collisions (broad phase) */
using Collision = std::pair<Particle *, Particle *>;
std::vector<Collision> broad_phase_brute(std::span<Particle> particles)
{
std::vector<Collision> collisions;
for (auto i = 0u; i < particles.size()-1; i++)
for (auto j = i+1; j < particles.size(); j++)
if (circle_circle_intersecting(particles[i].hitbox, particles[j].hitbox))
collisions.push_back(std::make_pair(&particles[i], &particles[j]));
return collisions;
}
std::vector<Collision> sweep_and_prune(std::span<Particle> particles)
{
std::vector<Particle *> axis_list{particles.size()};
for (auto i = 0u; i < particles.size(); i++)
axis_list[i] = &particles[i];
std::sort(axis_list.begin(), axis_list.end(), [](const auto &p, const auto &q) {
return p->hitbox.center.x < q->hitbox.center.x;
});
std::vector<Particle *> active;
std::vector<Collision> collisions;
for (auto *p : axis_list) {
std::erase_if(active, [&](const auto *q) {
return p->hitbox.left().x > q->hitbox.right().x;
});
for (auto *q : active)
collisions.push_back(std::make_pair(p, q));
active.push_back(p);
}
return collisions;
}
void test_sap()
{
std::vector<Particle> ps = {
Particle{ vec2{10.0f, 40.0f}, 5.0f, vec2{}, 0, 0 },
Particle{ vec2{15.0f, 100.0f}, 5.0f, vec2{}, 0, 0 },
Particle{ vec2{40.0f, 15.0f}, 5.0f, vec2{}, 0, 0 },
Particle{ vec2{60.0f, 40.0f}, 5.0f, vec2{}, 0, 0 },
Particle{ vec2{65.0f, 35.0f}, 5.0f, vec2{}, 0, 0 },
Particle{ vec2{76.0f, 90.0f}, 5.0f, vec2{}, 0, 0 },
};
auto collisions = sweep_and_prune(ps);
for (auto &c : collisions) {
auto &p = c.first;
auto &q = c.second;
fmt::print("collision between {} ({}, {}) and {} ({}, {})\n",
uintptr_t(p), p->hitbox.center.x, p->hitbox.center.y,
uintptr_t(q), q->hitbox.center.x, q->hitbox.center.y);
}
}
template <typename T, u32 N>
struct Grid {
struct PairHash {
std::size_t operator()(const std::pair<u32, u32> &p) const
{
return p.first * N + p.second;
}
};
std::unordered_map<std::pair<u32, u32>,
std::vector<T>,
PairHash> data;
void put_in_cell(u32 x, u32 y, T t)
{
// fmt::print("adding at {},{}\n", x, y);
assert(x < N && y < N);
auto &v = data[{x, y}];
v.push_back(t);
}
void put(vec2 tl, vec2 br, T t)
{
int start_row = std::max(0, (int) tl.x / (engine.screen_width() / 3));
int start_col = std::max(0, (int) tl.y / (engine.screen_width() / 3));
int end_row = std::min(2, (int) br.x / (engine.screen_height() / 3));
int end_col = std::min(2, (int) br.y / (engine.screen_height() / 3));
for (int row = start_row; row <= end_row; row++)
for (int col = start_col; col <= end_col; col++)
put_in_cell(row, col, t);
}
auto begin() { return data.begin(); }
auto end() { return data.end(); }
};
std::vector<Collision> uniform_grid(std::span<Particle> particles)
{
Grid<Particle *, 8> grid;
for (auto &p : particles)
grid.put(p.hitbox.top_left(), p.hitbox.bottom_right(), &p);
std::vector<Collision> collisions;
for (auto [pos, cell] : grid)
for (auto i = 0u; i < cell.size()-1; i++)
for (auto j = i+1; j < cell.size(); j++)
collisions.push_back(std::make_pair(cell[i], cell[j]));
return collisions;
}
std::vector<Collision> broad_phase(std::span<Particle> particles)
{
auto possible = sweep_and_prune(particles);
std::erase_if(possible, [&](const auto &c) {
auto &p = *c.first;
auto &q = *c.second;
return !circle_circle_intersecting(p.hitbox, q.hitbox);
});
return possible;
}
/*
* note that the k-d tree algorithm, as implemented like this, won't take count
* of the fact that some particles might be positioned right where the split
* occurs, making these particles part of both splitted areas.
* (this means it doesn't do shit and thus should only be taken as a
* demonstration on how to start implementing it. i've spent enough time with it
* already, i don't feel like finishing it).
*/
void kdtree(std::span<Particle *> particles, int depth, auto &&fn)
{
if (particles.size() <= 1)
return;
if (depth > 10) {
fn(particles);
return;
}
auto axis = depth % 2;
auto median = particles.size() / 2;
std::sort(particles.begin(), particles.end(), [&](const auto *p, const auto *q) {
return p->pos()[axis] < q->pos()[axis];
});
kdtree(particles.subspan(0, median), depth + 1, fn);
kdtree(particles.subspan(median), depth + 1, fn);
}
std::vector<Collision> broad_phase_kdtree(std::span<Particle> particles)
{
std::vector<Particle *> pointers;
std::vector<Collision> collisions;
for (auto &p : particles)
pointers.push_back(&p);
kdtree(pointers, 0, [&](std::span<Particle *> ps) {
for (auto i = 0u; i < ps.size(); i++) {
for (auto j = i+1; j < ps.size(); j++) {
auto &p = ps[i];
auto &q = ps[j];
if (circle_circle_intersecting(p->hitbox, q->hitbox)) {
collisions.push_back(std::make_pair(p, q));
}
}
}
});
return collisions;
}
/*
* particle and engine implementations
* (put here because one particle function depends on engine class
* and engine class depends on particle class)
*/
void Particle::update(float dt)
{
vel += accel * dt;
vec2 p1 = hitbox.center;
vec2 p2 = hitbox.center + vel * dt;
vec2 new_center = adjust_pos(p1, p2, hitbox.radius);
hitbox.center = new_center;
}
vec2 Particle::adjust_pos(vec2 p0, vec2 p1, float r)
{
vec2 res = p1;
if (auto wall = ccd_circle_line(p0.x, p1.x, r, 0); wall) { res.x = wall.value(); vel.x = -vel.x; }
if (auto wall = ccd_circle_line(p0.x, p1.x, r, engine.screen_width()); wall) { res.x = wall.value(); vel.x = -vel.x; }
if (auto wall = ccd_circle_line(p0.y, p1.y, r, 0); wall) { res.y = wall.value(); vel.y = -vel.y; }
if (auto wall = ccd_circle_line(p0.y, p1.y, r, engine.screen_height()); wall) { res.y = wall.value(); vel.y = -vel.y; }
return res;
}
void Engine::init(int width, int height)
{
SDL_Init(SDL_INIT_VIDEO);
window = SDL_CreateWindow("Particle sim", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, SDL_WINDOW_SHOWN);
rd = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
wnd_width = width;
wnd_height = height;
}
void Engine::deinit()
{
SDL_DestroyRenderer(rd);
SDL_DestroyWindow(window);
}
bool Engine::poll()
{
for (SDL_Event ev; SDL_PollEvent(&ev); ) {
switch (ev.type) {
case SDL_QUIT:
return false;
break;
}
}
return true;
}
void Engine::draw_one(float dt, vec2 pos, vec2 vel, int gfx_id, int particle_frame)
{
auto &gfx = gfx_handler[gfx_id];
// interpolate between frames
vec2 p = pos + vel * dt;
SDL_Rect src = { particle_frame * PARTICLE_SIZE, 0, PARTICLE_SIZE, PARTICLE_SIZE };
SDL_Rect dst = { int(p.x), int(p.y), PARTICLE_SIZE, PARTICLE_SIZE };
SDL_RenderCopy(rd, gfx.tex, &src, &dst);
}
void Engine::draw(float dt)
{
SDL_SetRenderDrawColor(rd, 0, 0, 0, 0xff);
SDL_RenderClear(rd);
for (auto &p : particles)
draw_one(dt, p.hitbox.top_left(), p.vel, p.gfx_id, p.frame);
SDL_SetRenderDrawColor(rd, 0xff, 0, 0, 0xff);
// draw_uniform_grid_lines(8);
SDL_RenderPresent(rd);
}
void Engine::draw_uniform_grid_lines(int grid_size)
{
for (int i = 1; i < grid_size; i++) {
vec2 start = { screen_width() / grid_size * i, 0 };
vec2 end = { screen_width() / grid_size * i, screen_height() };
SDL_RenderDrawLine(rd, int(start.x), int(start.y), int(end.x), int(end.y));
}
for (int i = 1; i < grid_size; i++) {
vec2 start = { 0, screen_height() / grid_size * i };
vec2 end = { screen_width(), screen_height() / grid_size * i };
SDL_RenderDrawLine(rd, int(start.x), int(start.y), int(end.x), int(end.y));
}
}
int Engine::load_gfx(std::string_view pathname)
{
auto *bmp = SDL_LoadBMP(pathname.data());
assert(bmp && "load of bmp image failed");
auto *tex = SDL_CreateTextureFromSurface(rd, bmp);
SDL_FreeSurface(bmp);
return gfx_handler.add({ .tex = tex, .size = {bmp->w, bmp->h} });
}
// note that dt may or may not be used depending on which game loop we use
// (look at the bottom for the 3 possible game loops)
void Engine::tick(float dt)
{
// fmt::print("tick\n");
for (auto &particle : particles)
particle.update(dt);
auto collisions = broad_phase(particles);
for (auto [p, q] : collisions) {
auto [v1, v2] = particle_collision(*p, *q);
p->vel = v1;
q->vel = v2;
}
}
void Engine::add_sprite(Particle particle)
{
particles.push_back(particle);
}
/* main stuff */
auto generate_particle(int screen_width, int screen_height, int id)
{
float radius = PARTICLE_SIZE/2;
vec2 pos{ random_between(0 + radius, screen_width - radius),
random_between(0 + radius, screen_height - radius), };
vec2 vel{ random_no_zero(PARTICLE_MIN_VEL, PARTICLE_MAX_VEL),
random_no_zero(PARTICLE_MIN_VEL, PARTICLE_MAX_VEL) };
return Particle{pos, radius, vel, id, int(random_integer_between(0, 5))};
}
void init(int width, int height, int num_particles)
{
std::srand(time(nullptr));
engine.init(width, height);
int gfx = engine.load_gfx("ball.bmp");
for (int i = 0; i < num_particles; i++)
engine.add_sprite(generate_particle(width, height, gfx));
}
void deinit()
{
engine.deinit();
}
// found somewhere on stack overflow
// it's a fixed time step loop that will play bad if a frame
// consistently takes more than TICK_INTERVAL.
void game_loop1()
{
u32 next = SDL_GetTicks() + TICK_INTERVAL;
for (bool running = true; running; ) {
next += TICK_INTERVAL;
running = engine.poll();
engine.tick(1);
engine.draw(0);
u32 now = SDL_GetTicks();
SDL_Delay(next <= now ? 0 : next - now);
}
}
// http://gameprogrammingpatterns.com/game-loop.html
// variable step game loop
void game_loop2()
{
auto last_time = SDL_GetTicks();
for (bool running = true; running; ) {
auto current = SDL_GetTicks();
auto elapsed = current - last_time;
running = engine.poll();
engine.tick(elapsed);
engine.draw(0);
last_time = current;
}
}
void game_loop3()
{
auto prev = SDL_GetTicks();
u32 lag = 0;
for (bool running = true; running; ) {
auto curr = SDL_GetTicks();
auto elapsed = curr - prev;
prev = curr;
lag += elapsed;
running = engine.poll();
while (lag >= TICK_INTERVAL) {
engine.tick(1);
lag -= TICK_INTERVAL;
}
engine.draw(lag);
}
}
void game_loop4()
{
u32 last = SDL_GetTicks();
float lag = 0.0f;
for (bool running = true; running; ) {
running = engine.poll();
u32 time = SDL_GetTicks();
u32 elapsed = time - last;
// Sleep if at least 1ms less than frame min
if (MIN_FRAME_TIME - i32(elapsed) > 1) {
SDL_Delay(MIN_FRAME_TIME - elapsed);
time = SDL_GetTicks();
elapsed = time - last;
}
float elapsed_f = float(elapsed);
if (elapsed_f > ELAPSED_MAX)
elapsed_f = ELAPSED_MAX;
lag += elapsed_f;
if (lag > TICK_DURATION) {
while (lag > TICK_DURATION) {
engine.tick(TICK_DURATION);
lag -= TICK_DURATION;
}
}
engine.draw(lag / TICK_DURATION);
last = time;
}
}
void game_loop()
{
game_loop4();
}
template <typename T>
std::optional<int> to_int(const T &str, unsigned base = 10)
{
int value = 0;
auto res = std::from_chars(str.data(), str.data() + str.size(), value, base);
if (res.ec != std::errc() || res.ptr != str.data() + str.size())
return std::nullopt;
return value;
}
int main(int argc, char *argv[])
{
static const cmdline::Argument args[] = {
{ 'h', "help", "print this help text" },
{ 'n', "num-particles", "set number of particles", cmdline::ParamType::Single },
{ 'w', "width", "set screen width", cmdline::ParamType::Single, "800" },
{ 'i', "height", "set screen height", cmdline::ParamType::Single, "600" },
};
auto result = cmdline::parse(argc, argv, args);
if (result.has['h']) {
cmdline::print_args(args);
return 0;
}
int width = SCREEN_WIDTH, height = SCREEN_HEIGHT, num = NUM_PARTICLES;
auto check_flag = [&](char flag, int &var) {
if (result.has[flag]) {
auto o = to_int(result.params[flag]);
if (!o) {
fmt::print(stderr, "invalid number {}\n", result.params[flag]);
exit(1);
}
var = o.value();
}
};
check_flag('w', width);
check_flag('i', height);
check_flag('n', num);
init(width, height, num);
game_loop();
deinit();
return 0;
}