examples/bassteroids/source/physics.cpp

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