examples/bassteroids/source/physics.cpp

   1 #include "physics.h"
   2 #include <msp/core/algorithm.h>
   3 #include <msp/game/transform.h>
   4 #include "physicalentity.h"
   5
   6 using namespace std;
   7 using namespace Msp;
   8
   9 Physics::Physics(Game::Stage &s):
  10         System(s),
  11         event_source(stage.get_event_bus()),
  12         observer(stage.get_event_bus())
  13 {
  14         observer.observe<Game::Events::EntityCreated>([this](auto &e){ entity_added(e); });
  15         observer.observe<Game::Events::EntityDestroyed>([this](auto &e){ entity_removed(e); });
  16
  17         stage.synthesize_initial_events(observer);
  18 }
  19
  20 void Physics::entity_added(const Game::Events::EntityCreated &e)
  21 {
  22         if(Game::Handle<PhysicalEntity> physical = dynamic_handle_cast<PhysicalEntity>(e.entity))
  23         {
  24                 for(Game::Handle<Game::Entity> p=e.entity->get_parent(); p; p=p->get_parent())
  25                         if(p->get_transform())
  26                                 return;
  27
  28                 SimulatedEntity sim_body;
  29                 sim_body.entity = physical;
  30                 if(physical->is_fixture())
  31                 {
  32                         entities.insert(entities.begin()+fixture_count, sim_body);
  33                         ++fixture_count;
  34                 }
  35                 else
  36                         entities.push_back(sim_body);
  37         }
  38 }
  39
  40 void Physics::entity_removed(const Game::Events::EntityDestroyed &e)
  41 {
  42         if(Game::Handle<PhysicalEntity> physical = dynamic_handle_cast<PhysicalEntity>(e.entity))
  43         {
  44                 auto i = find_member(entities, physical, &SimulatedEntity::entity);
  45                 if(i!=entities.end())
  46                 {
  47                         size_t index = distance(entities.begin(), i);
  48                         if(index<fixture_count)
  49                         {
  50                                 if(index+1!=fixture_count)
  51                                         *i = std::move(entities[fixture_count-1]);
  52                                 entities[fixture_count-1] = std::move(entities.back());
  53                         }
  54                         else
  55                                 *i = std::move(entities.back());
  56                         entities.pop_back();
  57                 }
  58         }
  59 }
  60
  61 void Physics::tick(Time::TimeDelta dt)
  62 {
  63         float dt_secs = dt/Time::sec;
  64
  65         for(unsigned i=0; i<fixture_count; ++i)
  66                 copy_in<true>(entities[i]);
  67         for(unsigned i=fixture_count; i<entities.size(); ++i)
  68                 copy_in<false>(entities[i]);
  69
  70         step(dt_secs);
  71
  72         collisions.clear();
  73         for(unsigned i=0; i<10; ++i)
  74         {
  75                 detect_collisions();
  76                 solve_collisions();
  77         }
  78
  79         apply_impulses();
  80
  81         for(unsigned i=0; i<fixture_count; ++i)
  82                 copy_out<true>(entities[i]);
  83         for(unsigned i=fixture_count; i<entities.size(); ++i)
  84                 copy_out<false>(entities[i]);
  85
  86         for(const Collision &c: collisions)
  87                 event_source.emit<Events::Collision>(entities[c.body1].entity->get_collider(), entities[c.body2].entity->get_collider());
  88 }
  89
  90 template<bool is_fixture>
  91 void Physics::copy_in(SimulatedEntity &entity)
  92 {
  93         Game::Handle<Game::Transform> transform = entity.entity->get_transform();
  94         entity.position = transform->get_position().slice<2>(0);
  95         const Geometry::Quaternion<float> &r = transform->get_rotation();
  96         entity.rotation = Geometry::atan2<float>(2*(r.a*r.d+r.b*r.c), 1-2*(r.c*r.c+r.d*r.d));
  97
  98         if constexpr(is_fixture)
  99         {
 100                 entity.inverse_mass = 0.0f;
 101                 entity.inverse_momi = 0.0f;
 102         }
 103         else
 104         {
 105                 Game::Handle<RigidBody> body = entity.entity->get_body();
 106                 entity.inverse_mass = 1.0f/body->get_mass();
 107                 entity.inverse_momi = 1.0f/body->get_moment_of_inertia();
 108                 entity.external_force = body->get_force();
 109                 entity.external_torque = body->get_torque();
 110                 entity.velocity = body->get_velocity();
 111                 entity.angular_velocity = body->get_angular_velocity();
 112         }
 113 }
 114
 115 template<bool is_fixture>
 116 void Physics::copy_out(SimulatedEntity &entity)
 117 {
 118         Game::Handle<Game::Transform> transform = entity.entity->get_transform();
 119         transform->set_position(compose(entity.position, 0.0f));
 120         transform->set_rotation(Geometry::Quaternion<float>::rotation(entity.rotation, LinAl::Vector<float, 3>(0, 0, 1)));
 121
 122         if constexpr(!is_fixture)
 123         {
 124                 Game::Handle<RigidBody> body = entity.entity->get_body();
 125                 body->set_velocity(entity.velocity);
 126                 body->set_angular_velocity(entity.angular_velocity);
 127                 body->clear_forces();
 128         }
 129 }
 130
 131 void Physics::step(float dt_secs)
 132 {
 133         for(unsigned i=fixture_count; i<entities.size(); ++i)
 134         {
 135                 SimulatedEntity &entity = entities[i];
 136
 137                 LinAl::Vector<float, 2> new_velocity = entity.velocity+entity.external_force*(dt_secs*entity.inverse_mass);
 138                 entity.position += (entity.velocity+new_velocity)*(dt_secs/2);
 139                 entity.velocity = new_velocity;
 140
 141                 Geometry::Angle<float> new_angular_velocity = entity.angular_velocity+Geometry::Angle<float>::from_radians(entity.external_torque*dt_secs*entity.inverse_momi);
 142                 entity.rotation = wrap_positive(entity.rotation+(entity.angular_velocity+new_angular_velocity)*(dt_secs/2));
 143                 entity.angular_velocity = new_angular_velocity;
 144         }
 145 }
 146
 147 void Physics::detect_collisions()
 148 {
 149         for(auto &c: collisions)
 150                 c.depth = 0.0f;
 151
 152         for(unsigned i=fixture_count; i<entities.size(); ++i)
 153         {
 154                 Game::Handle<PhysicalEntity> entity1 = entities[i].entity;
 155                 ColliderType type1 = entity1->get_collider()->get_type();
 156                 for(unsigned j=0; j<i; ++j)
 157                 {
 158                         Game::Handle<PhysicalEntity> entity2 = entities[j].entity;
 159                         ColliderType type2 = entity2->get_collider()->get_type();
 160                         if(type1==ColliderType::CIRCLE && type2==ColliderType::CIRCLE)
 161                                 collide_circle_circle(i, j);
 162                         else if(type1==ColliderType::CIRCLE && type2==ColliderType::BOX)
 163                                 collide_circle_box(i, j);
 164                         else if(type1==ColliderType::BOX && type2==ColliderType::CIRCLE)
 165                                 collide_circle_box(j, i);
 166                 }
 167         }
 168 }
 169
 170 void Physics::solve_collisions()
 171 {
 172         for(auto &e: entities)
 173         {
 174                 e.position_adjust = LinAl::Vector<float, 2>();
 175                 e.collision_count = 0;
 176         }
 177
 178         for(const auto &c: collisions)
 179         {
 180                 if(!c.depth)
 181                         continue;
 182
 183                 SimulatedEntity &entity1 = entities[c.body1];
 184                 SimulatedEntity &entity2 = entities[c.body2];
 185                 float inv_mass_sum = 1.0f/(entity1.inverse_mass+entity2.inverse_mass);
 186                 LinAl::Vector<float, 2> delta = c.normal*c.depth*inv_mass_sum;
 187                 if(c.body1>=fixture_count)
 188                 {
 189                         entity1.position_adjust += delta*entity1.inverse_mass;
 190                         ++entity1.collision_count;
 191                 }
 192                 if(c.body2>=fixture_count)
 193                 {
 194                         entity2.position_adjust -= delta*entity1.inverse_mass;
 195                         ++entity2.collision_count;
 196                 }
 197         }
 198
 199         for(auto &e: entities)
 200                 if(e.collision_count)
 201                         e.position += e.position_adjust/static_cast<float>(e.collision_count);
 202 }
 203
 204 void Physics::apply_impulses()
 205 {
 206         for(const auto &c: collisions)
 207         {
 208                 SimulatedEntity &entity1 = entities[c.body1];
 209                 SimulatedEntity &entity2 = entities[c.body2];
 210                 LinAl::Vector<float, 2> r1 = c.point-entity1.position;
 211                 LinAl::Vector<float, 2> r2 = c.point-entity2.position;
 212                 LinAl::Vector<float, 2> v_p1 = entity1.velocity+LinAl::Vector<float, 2>(-r1.y, r1.x)*entity1.angular_velocity.radians();
 213                 LinAl::Vector<float, 2> v_p2 = entity2.velocity+LinAl::Vector<float, 2>(-r2.y, r2.x)*entity2.angular_velocity.radians();
 214                 LinAl::Vector<float, 2> v_rel = v_p2-v_p1;
 215                 LinAl::Vector<float, 2> tangent = v_rel-c.normal*inner_product(v_rel, c.normal);
 216                 float v_tan = tangent.norm();
 217                 tangent = (v_tan>1e-5 ? normalize(tangent) : LinAl::Vector<float, 2>(-c.normal.y, c.normal.x));
 218                 float restitution = 1.0f;
 219                 float friction_coeff = 0.1f;
 220                 float inv_mass_sum = entity1.inverse_mass+entity2.inverse_mass;
 221                 float reaction = (1+restitution)*inner_product(v_rel, c.normal)/inv_mass_sum;
 222                 float friction = min(reaction*friction_coeff, v_tan/inv_mass_sum);
 223                 LinAl::Vector<float, 2> impulse = c.normal*reaction+tangent*friction;
 224                 entity1.velocity += impulse*entity1.inverse_mass;
 225                 entity2.velocity -= impulse*entity2.inverse_mass;
 226                 entity1.angular_velocity += Geometry::Angle<float>::from_radians(entity1.inverse_momi*(r1.x*impulse.y-r1.y*impulse.x));
 227                 entity2.angular_velocity -= Geometry::Angle<float>::from_radians(entity2.inverse_momi*(r2.x*impulse.y-r2.y*impulse.x));
 228         }
 229 }
 230
 231 Physics::Collision &Physics::get_collision(unsigned i, unsigned j)
 232 {
 233         for(auto &c: collisions)
 234                 if((c.body1==i && c.body2==j) || (c.body1==j && c.body2==i))
 235                         return c;
 236
 237         Collision &c = collisions.emplace_back();
 238         c.body1 = i;
 239         c.body2 = j;
 240         return c;
 241 }
 242
 243 void Physics::collide_circle_circle(unsigned i, unsigned j)
 244 {
 245         const LinAl::Vector<float, 2> &pos1 = entities[i].position;
 246         const LinAl::Vector<float, 2> &pos2 = entities[j].position;
 247         float r1 = entities[i].entity->get_collider()->get_radius();
 248         float r2 = entities[j].entity->get_collider()->get_radius();
 249
 250         /* Points in the direction the first body needs to move in to clear the
 251         penetration */
 252         LinAl::Vector<float, 2> delta = pos1-pos2;
 253         float d_sq = inner_product(delta, delta);
 254         float r_sum = r1+r2;
 255         if(d_sq<r_sum*r_sum)
 256         {
 257                 Collision &collision = get_collision(i, j);
 258                 collision.normal = normalize(delta);
 259                 collision.depth = r1+r2-sqrt(d_sq);
 260                 collision.point = pos1-collision.normal*(r1-collision.depth/2);
 261                 if(collision.body1!=i)
 262                         collision.normal = -collision.normal;
 263         }
 264 }
 265
 266 void Physics::collide_circle_box(unsigned i, unsigned j)
 267 {
 268         const LinAl::Vector<float, 2> &pos1 = entities[i].position;
 269         const LinAl::Vector<float, 2> &pos2 = entities[j].position;
 270         float radius = entities[i].entity->get_collider()->get_radius();
 271         LinAl::Vector<float, 2> half_size = entities[j].entity->get_collider()->get_size()/2.0f;
 272
 273         LinAl::Vector<float, 2> delta = pos1-pos2;
 274         float c = cos(entities[j].rotation);
 275         float s = sin(entities[j].rotation);
 276         LinAl::Vector<float, 2> local_delta(c*delta.x+s*delta.y, c*delta.y-s*delta.x);
 277         LinAl::Vector<float, 2> local_closest(clamp(local_delta.x, -half_size.x, half_size.x), clamp(local_delta.y, -half_size.y, half_size.y));
 278         LinAl::Vector<float, 2> local_cdelta = local_delta-local_closest;
 279         float d_sq = inner_product(local_cdelta, local_cdelta);
 280
 281         if(d_sq<radius*radius)
 282         {
 283                 Collision &collision = get_collision(i, j);
 284                 if(d_sq>1e-10)
 285                 {
 286                         collision.normal = normalize(LinAl::Vector<float, 2>(c*local_cdelta.x-s*local_cdelta.y, c*local_cdelta.y+s*local_cdelta.x));
 287                         collision.depth = radius-sqrt(d_sq);
 288                 }
 289                 else
 290                 {
 291                         LinAl::Vector<float, 2> inside_dist(half_size.x-abs(local_delta.x), half_size.y-abs(local_delta.y));
 292                         if(inside_dist.x<inside_dist.y)
 293                         {
 294                                 collision.normal = LinAl::Vector<float, 2>(c, s) * (local_delta.x<0 ? -1.0f : 1.0f);
 295                                 collision.depth = radius+inside_dist.x;
 296                         }
 297                         else
 298                         {
 299                                 collision.normal = LinAl::Vector<float, 2>(-s, c) * (local_delta.y<0 ? -1.0f : 1.0f);
 300                                 collision.depth = radius+inside_dist.y;
 301                         }
 302                 }
 303                 collision.point = pos1-collision.normal*(radius-collision.depth/2);
 304                 if(collision.body1!=i)
 305                         collision.normal = -collision.normal;
 306         }
 307 }