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.velocity = body->get_velocity();
  79         }
  80 }
  81
  82 template<bool is_fixture>
  83 void Physics::copy_out(SimulatedEntity &entity)
  84 {
  85         Game::Handle<Game::Transform> transform = entity.entity->get_transform();
  86         transform->set_position(compose(entity.position, 0.0f));
  87         transform->set_rotation(Geometry::Quaternion<float>::rotation(entity.rotation, LinAl::Vector<float, 3>(0, 0, 1)));
  88
  89         if constexpr(!is_fixture)
  90         {
  91                 Game::Handle<RigidBody> body = entity.entity->get_body();
  92                 body->set_velocity(entity.velocity);
  93         }
  94 }
  95
  96 void Physics::step(float dt_secs)
  97 {
  98         for(unsigned i=fixture_count; i<entities.size(); ++i)
  99         {
 100                 SimulatedEntity &entity = entities[i];
 101
 102                 LinAl::Vector<float, 2> new_velocity = entity.velocity+entity.external_force*dt_secs*entity.inverse_mass;
 103                 entity.position += (entity.velocity+new_velocity)*(dt_secs/2);
 104                 entity.velocity = new_velocity;
 105         }
 106 }
 107
 108 void Physics::detect_collisions()
 109 {
 110         for(auto &c: collisions)
 111                 c.depth = 0.0f;
 112
 113         for(unsigned i=fixture_count; i<entities.size(); ++i)
 114         {
 115                 Game::Handle<PhysicalEntity> entity1 = entities[i].entity;
 116                 ColliderType type1 = entity1->get_collider()->get_type();
 117                 for(unsigned j=0; j<i; ++j)
 118                 {
 119                         Game::Handle<PhysicalEntity> entity2 = entities[j].entity;
 120                         ColliderType type2 = entity2->get_collider()->get_type();
 121                         if(type1==ColliderType::CIRCLE && type2==ColliderType::CIRCLE)
 122                                 collide_circle_circle(i, j);
 123                         else if(type1==ColliderType::CIRCLE && type2==ColliderType::BOX)
 124                                 collide_circle_box(i, j);
 125                         else if(type1==ColliderType::BOX && type2==ColliderType::CIRCLE)
 126                                 collide_circle_box(j, i);
 127                 }
 128         }
 129 }
 130
 131 void Physics::solve_collisions()
 132 {
 133         for(auto &e: entities)
 134         {
 135                 e.position_adjust = LinAl::Vector<float, 2>();
 136                 e.collision_count = 0;
 137         }
 138
 139         for(const auto &c: collisions)
 140         {
 141                 if(!c.depth)
 142                         continue;
 143
 144                 SimulatedEntity &entity1 = entities[c.body1];
 145                 SimulatedEntity &entity2 = entities[c.body2];
 146                 float inv_mass_sum = 1.0f/(entity1.inverse_mass+entity2.inverse_mass);
 147                 LinAl::Vector<float, 2> delta = c.normal*c.depth*inv_mass_sum;
 148                 if(c.body1>=fixture_count)
 149                 {
 150                         entity1.position_adjust += delta*entity1.inverse_mass;
 151                         ++entity1.collision_count;
 152                 }
 153                 if(c.body2>=fixture_count)
 154                 {
 155                         entity2.position_adjust -= delta*entity1.inverse_mass;
 156                         ++entity2.collision_count;
 157                 }
 158         }
 159
 160         for(auto &e: entities)
 161                 if(e.collision_count)
 162                         e.position += e.position_adjust/static_cast<float>(e.collision_count);
 163 }
 164
 165 void Physics::apply_impulses()
 166 {
 167         for(const auto &c: collisions)
 168         {
 169                 SimulatedEntity &entity1 = entities[c.body1];
 170                 SimulatedEntity &entity2 = entities[c.body2];
 171                 LinAl::Vector<float, 2> v_rel = entity2.velocity-entity1.velocity;
 172                 float restitution = 1.0f;
 173                 float inv_mass_sum = entity1.inverse_mass+entity2.inverse_mass;
 174                 float impulse = (1+restitution)*inner_product(v_rel, c.normal)/inv_mass_sum;
 175                 entity1.velocity += c.normal*(impulse*entity1.inverse_mass);
 176                 entity2.velocity -= c.normal*(impulse*entity2.inverse_mass);
 177         }
 178 }
 179
 180 Physics::Collision &Physics::get_collision(unsigned i, unsigned j)
 181 {
 182         for(auto &c: collisions)
 183                 if((c.body1==i && c.body2==j) || (c.body1==j && c.body2==i))
 184                         return c;
 185
 186         Collision &c = collisions.emplace_back();
 187         c.body1 = i;
 188         c.body2 = j;
 189         return c;
 190 }
 191
 192 void Physics::collide_circle_circle(unsigned i, unsigned j)
 193 {
 194         const LinAl::Vector<float, 2> &pos1 = entities[i].position;
 195         const LinAl::Vector<float, 2> &pos2 = entities[j].position;
 196         float r1 = entities[i].entity->get_collider()->get_radius();
 197         float r2 = entities[j].entity->get_collider()->get_radius();
 198
 199         /* Points in the direction the first body needs to move in to clear the
 200         penetration */
 201         LinAl::Vector<float, 2> delta = pos1-pos2;
 202         float d_sq = inner_product(delta, delta);
 203         float r_sum = r1+r2;
 204         if(d_sq<r_sum*r_sum)
 205         {
 206                 Collision &collision = get_collision(i, j);
 207                 collision.normal = normalize(delta);
 208                 collision.depth = r1+r2-sqrt(d_sq);
 209                 collision.point = pos1-collision.normal*(r1-collision.depth/2);
 210                 if(collision.body1!=i)
 211                         collision.normal = -collision.normal;
 212         }
 213 }
 214
 215 void Physics::collide_circle_box(unsigned i, unsigned j)
 216 {
 217         const LinAl::Vector<float, 2> &pos1 = entities[i].position;
 218         const LinAl::Vector<float, 2> &pos2 = entities[j].position;
 219         float radius = entities[i].entity->get_collider()->get_radius();
 220         LinAl::Vector<float, 2> half_size = entities[j].entity->get_collider()->get_size()/2.0f;
 221
 222         LinAl::Vector<float, 2> delta = pos1-pos2;
 223         float c = cos(entities[j].rotation);
 224         float s = sin(entities[j].rotation);
 225         LinAl::Vector<float, 2> local_delta(c*delta.x+s*delta.y, c*delta.y-s*delta.x);
 226         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));
 227         LinAl::Vector<float, 2> local_cdelta = local_delta-local_closest;
 228         float d_sq = inner_product(local_cdelta, local_cdelta);
 229         if(d_sq<radius*radius)
 230         {
 231                 Collision &collision = get_collision(i, j);
 232                 collision.normal = normalize(LinAl::Vector<float, 2>(c*local_cdelta.x-s*local_cdelta.y, c*local_cdelta.y+s*local_cdelta.x));
 233                 collision.depth = radius-sqrt(d_sq);
 234                 collision.point = pos1-collision.normal*(radius-collision.depth/2);
 235                 if(collision.body1!=i)
 236                         collision.normal = -collision.normal;
 237         }
 238 }