ref: 55c02ff080dfe0abd113a2d930c39f2da6e9316b
dir: /include-demo/chadphys.h/
#ifndef CHAD_PHYS_H
#define CHAD_PHYS_H
#include "3dMath.h"
typedef struct {
aabb shape; //c.d[3] is sphere radius.
//if it's zero or less, it's not a sphere, it's a box
mat4 localt; //Local Transform.
vec3 v; //velocity
vec3 a; //Body specific acceleration, combined with gravity
f_ mass; //0 means kinematic, or static. Defaults to zero.
f_ bounciness; //default 0, put portion of displacement into velocity.
f_ airfriction; //default 1, multiplied by velocity every time timestep.
f_ friction; //default 0.1
} phys_body;
typedef struct{
vec3 g; //gravity
phys_body** bodies;
f_ ms; //max speed
int nbodies; //number of bodies
} phys_world;
static inline void initPhysBody(phys_body* body){
body->shape = (aabb){
.c=(vec4){.d[0] = 0,.d[1] = 0,.d[2] = 0,.d[3] = 0},
.e=(vec3){.d[0] = 0,.d[1] = 0,.d[2] = 0}
};
body->mass = 0;
body->bounciness = 0;
body->friction = 0.99; //The amount of coplanar velocity preserved in collisions.
body->airfriction = 1.0;
body->a = (vec3){.d[0] = 0,.d[1] = 0,.d[2] = 0};
body->localt = identitymat4();
}
static inline mat4 getPhysBodyRenderTransform(phys_body* body){
return multm4(
translate(downv4(body->shape.c)),
body->localt
);
}
//Check for and, if necessary, resolve colliding bodies.
static inline void resolveBodies(phys_body* a, phys_body* b){
if(a->mass > 0 || b->mass > 0){ //Perform a preliminary check. Do we even have to do anything?
/*We must do shit*/
} else {return;}
/*Optimized for branch prediction.*/
vec4 penvec = (vec4){
.d[0]=0,
.d[1]=0,
.d[2]=0,
.d[3]=0
};
/*Check if the two bodies are colliding.*/
if(a->shape.c.d[3] > 0 && b->shape.c.d[3] > 0) //Both Spheres!
{
penvec = spherevsphere(a->shape.c, b->shape.c);
} else if(a->shape.c.d[3] <= 0 && b->shape.c.d[3] <= 0) //Both boxes!
{
penvec = boxvbox(a->shape,b->shape);
} else if (a->shape.c.d[3] > 0 && b->shape.c.d[3] <= 0) //a is a sphere, b is a box
{
penvec = spherevaabb(a->shape.c,b->shape);
} else if (a->shape.c.d[3] <= 0 && b->shape.c.d[3] > 0){ //a is a box, b is a sphere
penvec = spherevaabb(b->shape.c,a->shape);
penvec.d[0] *= -1;
penvec.d[1] *= -1;
penvec.d[2] *= -1;
}
#ifdef CHADPHYS_DEBUG
else {
puts("\nInvalid configuration. Error.\n");
}
#endif
if(penvec.d[3] <= 0) return; //No penetration detected, or invalid configuration.
vec3 penvecnormalized = scalev3(1.0/penvec.d[3], downv4(penvec)); //the penetration vector points into B...
f_ friction = a->friction * b->friction;
//We now have the penetration vector. There is a penetration.
//determine how much each should be displaced by.
//The penvec points INTO A and is of length penvec.d[3]
f_ bdisplacefactor = a->mass / (a->mass + b->mass);
f_ adisplacefactor = b->mass / (a->mass + b->mass);
vec3 comvel;
if(!(a->mass > 0)) {
adisplacefactor = 0; bdisplacefactor = 1;
}else if(!(b->mass > 0)) {
bdisplacefactor = 0; adisplacefactor = 1;
}
comvel = addv3( scalev3(bdisplacefactor, a->v), scalev3(adisplacefactor, b->v));
if(a->mass > 0){
vec4 displacea = scalev4(-adisplacefactor, penvec);
vec3 a_relvel = subv3(a->v, comvel);
vec3 a_planarvel = subv3(a_relvel,
scalev3(
dotv3(a_relvel, penvecnormalized),
penvecnormalized
)
);
a->shape.c.d[0] += displacea.d[0];
a->shape.c.d[1] += displacea.d[1];
a->shape.c.d[2] += displacea.d[2];
a->v = addv3( comvel, scalev3(1-friction, a_planarvel) ); //The center of mass velocity, plus a portion of coplanar velocity.
a->v = addv3(a->v, scalev3( a->bounciness, downv4(displacea) ) );
}
if(b->mass > 0){
vec4 displaceb = scalev4(bdisplacefactor, penvec);
vec3 b_relvel = subv3(b->v, comvel);
vec3 b_planarvel = subv3(b_relvel, //brelvel - portion of brelvel in the direction of penvecnormalized
scalev3(
dotv3(b_relvel, penvecnormalized), //the component in that direction
penvecnormalized //that direction
)
);
#pragma omp simd
for(int i = 0; i < 3; i++)
b->shape.c.d[i] += displaceb.d[i];
b->v = addv3(comvel, scalev3(1-friction, b_planarvel) ); //The center of mass velocity, plus a portion of coplanar velocity.
b->v = addv3(b->v, scalev3( b->bounciness, downv4(displaceb) ) );
}
}
static inline void stepPhysWorld(phys_world* world, const int collisioniter){
for(int i = 0; i < world->nbodies; i++)
if(world->bodies[i] && world->bodies[i]->mass > 0){
phys_body* body = world->bodies[i];
vec3 bodypos = addv3(downv4(body->shape.c),body->v);
body->shape.c.d[0] = bodypos.d[0];
body->shape.c.d[1] = bodypos.d[1];
body->shape.c.d[2] = bodypos.d[2];
body->v = addv3(body->v, body->a);
body->v = addv3(body->v, world->g);
while(dotv3(body->v, body->v) > world->ms) {
body->v = scalev3(0.9, body->v);
}
}
//Resolve collisions (if any)
for(int iter = 0; iter < collisioniter; iter++)
for(int i = 0; i < (int)(world->nbodies-1); i++)
if(world->bodies[i])
for(int j = i+1; j < (int)world->nbodies; j++)
if(world->bodies[j])
resolveBodies(world->bodies[i], world->bodies[j]);
}
#endif