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         observer(stage.get_event_bus())
  12 {
  13         observer.observe<Game::Events::EntityCreated>([this](auto &e){ entity_added(e); });
  14
  15         stage.synthesize_initial_events(observer);
  16 }
  17
  18 void Physics::entity_added(const Game::Events::EntityCreated &e)
  19 {
  20         if(Game::Handle<PhysicalEntity> physical = dynamic_handle_cast<PhysicalEntity>(e.entity))
  21         {
  22                 for(Game::Handle<Game::Entity> p=e.entity->get_parent(); p; p=p->get_parent())
  23                         if(p->get_transform())
  24                                 return;
  25
  26                 SimulatedEntity sim_body;
  27                 sim_body.entity = physical;
  28                 if(physical->is_fixture())
  29                 {
  30                         entities.insert(entities.begin()+fixture_count, sim_body);
  31                         ++fixture_count;
  32                 }
  33                 else
  34                         entities.push_back(sim_body);
  35         }
  36 }
  37
  38 void Physics::tick(Time::TimeDelta dt)
  39 {
  40         float dt_secs = dt/Time::sec;
  41
  42         for(unsigned i=0; i<fixture_count; ++i)
  43                 copy_in<true>(entities[i]);
  44         for(unsigned i=fixture_count; i<entities.size(); ++i)
  45                 copy_in<false>(entities[i]);
  46
  47         step(dt_secs);
  48
  49         collisions.clear();
  50         for(unsigned i=0; i<10; ++i)
  51         {
  52                 detect_collisions();
  53                 solve_collisions();
  54         }
  55
  56         apply_impulses();
  57
  58         for(unsigned i=0; i<fixture_count; ++i)
  59                 copy_out<true>(entities[i]);
  60         for(unsigned i=fixture_count; i<entities.size(); ++i)
  61                 copy_out<false>(entities[i]);
  62 }
  63
  64 template<bool is_fixture>
  65 void Physics::copy_in(SimulatedEntity &entity)
  66 {
  67         Game::Handle<Game::Transform> transform = entity.entity->get_transform();
  68         entity.position = transform->get_position().slice<2>(0);
  69         const Geometry::Quaternion<float> &r = transform->get_rotation();
  70         entity.rotation = Geometry::atan2<float>(2*(r.a*r.d+r.b*r.c), 1-2*(r.c*r.c+r.d*r.d));
  71
  72         if constexpr(is_fixture)
  73                 entity.inverse_mass = 0.0f;
  74         else
  75         {
  76                 Game::Handle<RigidBody> body = entity.entity->get_body();
  77                 entity.inverse_mass = 1.0f/body->get_mass();
  78                 entity.moment_of_inertia = body->get_moment_of_inertia();
  79                 entity.external_force = body->get_force();
  80                 entity.external_torque = body->get_torque();
  81                 entity.velocity = body->get_velocity();
  82                 entity.angular_velocity = body->get_angular_velocity();
  83         }
  84 }
  85
  86 template<bool is_fixture>
  87 void Physics::copy_out(SimulatedEntity &entity)
  88 {
  89         Game::Handle<Game::Transform> transform = entity.entity->get_transform();
  90         transform->set_position(compose(entity.position, 0.0f));
  91         transform->set_rotation(Geometry::Quaternion<float>::rotation(entity.rotation, LinAl::Vector<float, 3>(0, 0, 1)));
  92
  93         if constexpr(!is_fixture)
  94         {
  95                 Game::Handle<RigidBody> body = entity.entity->get_body();
  96                 body->set_velocity(entity.velocity);
  97                 body->set_angular_velocity(entity.angular_velocity);
  98                 body->clear_forces();
  99         }
 100 }
 101
 102 void Physics::step(float dt_secs)
 103 {
 104         for(unsigned i=fixture_count; i<entities.size(); ++i)
 105         {
 106                 SimulatedEntity &entity = entities[i];
 107
 108                 LinAl::Vector<float, 2> new_velocity = entity.velocity+entity.external_force*dt_secs*entity.inverse_mass;
 109                 entity.position += (entity.velocity+new_velocity)*(dt_secs/2);
 110                 entity.velocity = new_velocity;
 111
 112                 Geometry::Angle<float> new_angular_velocity = entity.angular_velocity+Geometry::Angle<float>::from_radians(entity.external_torque*(dt_secs/entity.moment_of_inertia));
 113                 entity.rotation = wrap_positive(entity.rotation+(entity.angular_velocity+new_angular_velocity)*(dt_secs/2));
 114                 entity.angular_velocity = new_angular_velocity;
 115         }
 116 }
 117
 118 void Physics::detect_collisions()
 119 {
 120         for(auto &c: collisions)
 121                 c.depth = 0.0f;
 122
 123         for(unsigned i=fixture_count; i<entities.size(); ++i)
 124         {
 125                 Game::Handle<PhysicalEntity> entity1 = entities[i].entity;
 126                 ColliderType type1 = entity1->get_collider()->get_type();
 127                 for(unsigned j=0; j<i; ++j)
 128                 {
 129                         Game::Handle<PhysicalEntity> entity2 = entities[j].entity;
 130                         ColliderType type2 = entity2->get_collider()->get_type();
 131                         if(type1==ColliderType::CIRCLE && type2==ColliderType::CIRCLE)
 132                                 collide_circle_circle(i, j);
 133                         else if(type1==ColliderType::CIRCLE && type2==ColliderType::BOX)
 134                                 collide_circle_box(i, j);
 135                         else if(type1==ColliderType::BOX && type2==ColliderType::CIRCLE)
 136                                 collide_circle_box(j, i);
 137                 }
 138         }
 139 }
 140
 141 void Physics::solve_collisions()
 142 {
 143         for(auto &e: entities)
 144         {
 145                 e.position_adjust = LinAl::Vector<float, 2>();
 146                 e.collision_count = 0;
 147         }
 148
 149         for(const auto &c: collisions)
 150         {
 151                 if(!c.depth)
 152                         continue;
 153
 154                 SimulatedEntity &entity1 = entities[c.body1];
 155                 SimulatedEntity &entity2 = entities[c.body2];
 156                 float inv_mass_sum = 1.0f/(entity1.inverse_mass+entity2.inverse_mass);
 157                 LinAl::Vector<float, 2> delta = c.normal*c.depth*inv_mass_sum;
 158                 if(c.body1>=fixture_count)
 159                 {
 160                         entity1.position_adjust += delta*entity1.inverse_mass;
 161                         ++entity1.collision_count;
 162                 }
 163                 if(c.body2>=fixture_count)
 164                 {
 165                         entity2.position_adjust -= delta*entity1.inverse_mass;
 166                         ++entity2.collision_count;
 167                 }
 168         }
 169
 170         for(auto &e: entities)
 171                 if(e.collision_count)
 172                         e.position += e.position_adjust/static_cast<float>(e.collision_count);
 173 }
 174
 175 void Physics::apply_impulses()
 176 {
 177         for(const auto &c: collisions)
 178         {
 179                 SimulatedEntity &entity1 = entities[c.body1];
 180                 SimulatedEntity &entity2 = entities[c.body2];
 181                 LinAl::Vector<float, 2> v_rel = entity2.velocity-entity1.velocity;
 182                 float restitution = 1.0f;
 183                 float inv_mass_sum = entity1.inverse_mass+entity2.inverse_mass;
 184                 float impulse = (1+restitution)*inner_product(v_rel, c.normal)/inv_mass_sum;
 185                 entity1.velocity += c.normal*(impulse*entity1.inverse_mass);
 186                 entity2.velocity -= c.normal*(impulse*entity2.inverse_mass);
 187         }
 188 }
 189
 190 Physics::Collision &Physics::get_collision(unsigned i, unsigned j)
 191 {
 192         for(auto &c: collisions)
 193                 if((c.body1==i && c.body2==j) || (c.body1==j && c.body2==i))
 194                         return c;
 195
 196         Collision &c = collisions.emplace_back();
 197         c.body1 = i;
 198         c.body2 = j;
 199         return c;
 200 }
 201
 202 void Physics::collide_circle_circle(unsigned i, unsigned j)
 203 {
 204         const LinAl::Vector<float, 2> &pos1 = entities[i].position;
 205         const LinAl::Vector<float, 2> &pos2 = entities[j].position;
 206         float r1 = entities[i].entity->get_collider()->get_radius();
 207         float r2 = entities[j].entity->get_collider()->get_radius();
 208
 209         /* Points in the direction the first body needs to move in to clear the
 210         penetration */
 211         LinAl::Vector<float, 2> delta = pos1-pos2;
 212         float d_sq = inner_product(delta, delta);
 213         float r_sum = r1+r2;
 214         if(d_sq<r_sum*r_sum)
 215         {
 216                 Collision &collision = get_collision(i, j);
 217                 collision.normal = normalize(delta);
 218                 collision.depth = r1+r2-sqrt(d_sq);
 219                 collision.point = pos1-collision.normal*(r1-collision.depth/2);
 220                 if(collision.body1!=i)
 221                         collision.normal = -collision.normal;
 222         }
 223 }
 224
 225 void Physics::collide_circle_box(unsigned i, unsigned j)
 226 {
 227         const LinAl::Vector<float, 2> &pos1 = entities[i].position;
 228         const LinAl::Vector<float, 2> &pos2 = entities[j].position;
 229         float radius = entities[i].entity->get_collider()->get_radius();
 230         LinAl::Vector<float, 2> half_size = entities[j].entity->get_collider()->get_size()/2.0f;
 231
 232         LinAl::Vector<float, 2> delta = pos1-pos2;
 233         float c = cos(entities[j].rotation);
 234         float s = sin(entities[j].rotation);
 235         LinAl::Vector<float, 2> local_delta(c*delta.x+s*delta.y, c*delta.y-s*delta.x);
 236         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));
 237         LinAl::Vector<float, 2> local_cdelta = local_delta-local_closest;
 238         float d_sq = inner_product(local_cdelta, local_cdelta);
 239         if(d_sq<radius*radius)
 240         {
 241                 Collision &collision = get_collision(i, j);
 242                 collision.normal = normalize(LinAl::Vector<float, 2>(c*local_cdelta.x-s*local_cdelta.y, c*local_cdelta.y+s*local_cdelta.x));
 243                 collision.depth = radius-sqrt(d_sq);
 244                 collision.point = pos1-collision.normal*(radius-collision.depth/2);
 245                 if(collision.body1!=i)
 246                         collision.normal = -collision.normal;
 247         }
 248 }