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#include <u.h>
#include <libc.h>
#include <draw.h>
#include "galaxy.h"
void
growquads(void)
{
quads.max *= 2;
quads.a = realloc(quads.a, sizeof(Quad) * quads.max);
if(quads.a == nil)
sysfatal("could not realloc quads: %r");
}
Quad*
quad(Body *b)
{
Quad *q;
if(quads.l == quads.max)
return nil;
q = quads.a + quads.l++;
memset(q->c, 0, sizeof(QB)*4);
q->x = b->x;
q->y = b->y;
q->mass = b->mass;
return q;
}
int
quadins(Body *nb, double size)
{
QB *qb;
Quad *q;
Body *b;
double mass, qx, qy;
uint qxy;
int d;
if(space.t == EMPTY) {
space.t = BODY;
space.b = nb;
return 0;
}
d = 0;
qb = &space;
qx = 0.0;
qy = 0.0;
for(;;) {
if(qb->t == BODY) {
b = qb->b;
qxy = b->x < qx ? 0 : 1;
qxy |= b->y < qy ? 0 : 2;
qb->t = QUAD;
if((qb->q = quad(b)) == nil)
return -1;
qb->q->c[qxy].t = BODY;
qb->q->c[qxy].b = b;
}
q = qb->q;
mass = q->mass + nb->mass;
q->x = (q->x*q->mass + nb->x*nb->mass) / mass;
q->y = (q->y*q->mass + nb->y*nb->mass) / mass;
q->mass = mass;
qxy = nb->x < qx ? 0 : 1;
qxy |= nb->y < qy ? 0 : 2;
if(q->c[qxy].t == EMPTY) {
q->c[qxy].t = BODY;
q->c[qxy].b = nb;
STATS(if(d > quaddepth) quaddepth = d;)
return 0;
}
STATS(d++;)
qb = &q->c[qxy];
size /= 2;
qx += qxy&1 ? size/2 : -size/2;
qy += qxy&2 ? size/2 : -size/2;
}
}
void
quadcalc(Body *b, QB qb, double size)
{
double fx÷❨m₁m₂❩, fy÷❨m₁m₂❩, dx, dy, h, G÷h³;
for(;;) switch(qb.t) {
default:
sysfatal("quadcalc: No such type");
case EMPTY:
return;
case BODY:
if(qb.b == b)
return;
dx = qb.b->x - b->x;
dy = qb.b->y - b->y;
h = hypot(hypot(dx, dy), ε);
G÷h³ = G / (h*h*h);
fx÷❨m₁m₂❩ = dx * G÷h³;
fy÷❨m₁m₂❩ = dy * G÷h³;
b->newa.x += fx÷❨m₁m₂❩ * qb.b->mass;
b->newa.y += fy÷❨m₁m₂❩ * qb.b->mass;
STATS(calcs++;)
return;
case QUAD:
dx = qb.q->x - b->x;
dy = qb.q->y - b->y;
h = hypot(dx, dy);
if(h != 0.0 && size/h < θ) {
h = hypot(h, ε);
G÷h³ = G / (h*h*h);
fx÷❨m₁m₂❩ = dx * G÷h³;
fy÷❨m₁m₂❩ = dy * G÷h³;
b->newa.x += fx÷❨m₁m₂❩ * qb.q->mass;
b->newa.y += fy÷❨m₁m₂❩ * qb.q->mass;
STATS(calcs++;)
return;
}
size /= 2;
quadcalc(b, qb.q->c[0], size);
quadcalc(b, qb.q->c[1], size);
quadcalc(b, qb.q->c[2], size);
qb = qb.q->c[3];
break; /* quadcalc(q->q[3], b, size); */
}
}
void
quadsinit(void)
{
quads.a = calloc(5, sizeof(Body));
if(quads.a == nil)
sysfatal("could not allocate quads: %r");
quads.l = 0;
quads.max = 5;
}
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