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#include <math.h>
#include <stdbool.h>
#include <stddef.h>
#include "dat.h"
static void mink(Body *a, Body *b, float *minx, float *miny, float *maxx, float *maxy);
static int checkcollision(Body *a, Body *b);
static void resolvecoll(Body *a, Body *b, float p[2]);
static EntityCollision ecoll[2048];
static int ecollstart, ecollend, ecollsi;
void
entphysics(float delta)
{
for(int i = 0; i < ebufi; i++) {
Entity *e = entitybuffer + i;
if(!e->active)
continue;
for(int y = 0; y < map_height; y++)
for(int x = 0; x < map_width; x++) {
if(!map_data[x + y * map_width])
continue;
Body b = {
.pos = {
x * ENTITY_SIZE * 2.0,
y * ENTITY_SIZE * 2.0,
},
.size = { ENTITY_SIZE, ENTITY_SIZE },
};
if(checkcollision(&e->body, &b)) {
float p[2];
resolvecoll(&e->body, &b, p);
for(int i = 0; i < 2; i++)
e->body.pos[i] -= p[i];
if(p[0] != 0.0) {
e->body.vel[0] = 0;
} else {
e->body.vel[1] = 0;
}
}
}
for(int j = i; j >= 0; j--) {
Entity *f = entitybuffer + j;
if(!f->active || f == e)
continue;
if(checkcollision(&e->body, &f->body)) {
EntityCollision cl;
cl.self = e;
cl.target = f;
enqcoll(&cl);
}
}
}
for(int i = 0; i < ebufi; i++) {
Entity *e = entitybuffer + i;
if(!e->active)
continue;
for(int j = 0; j < 2; j++)
e->body.pos[j] += e->body.vel[j] * delta;
}
}
int
checkcollision(Body *a, Body *b)
{
float minx, miny, maxx, maxy;
mink(a, b, &minx, &miny, &maxx, &maxy);
return minx < 0 && maxx > 0 && miny < 0 && maxy > 0;
}
void
resolvecoll(Body *a, Body *b, float p[2])
{
float minx, miny, maxx, maxy;
mink(a, b, &minx, &miny, &maxx, &maxy);
float hx = fabsf(minx) < fabsf(maxx) ? fabsf(minx) : fabsf(maxx);
float hy = fabsf(miny) < fabsf(maxy) ? fabsf(miny) : fabsf(maxy);
if(hx < hy) {
p[1] = 0;
p[0] = hx * (fabsf(minx) < fabsf(maxx) ? -1.0 : 1.0);
} else {
p[0] = 0;
p[1] = hy * (fabsf(miny) < fabsf(maxy) ? -1.0 : 1.0);
}
}
void
mink(Body *a, Body *b, float *minx, float *miny, float *maxx, float *maxy)
{
float p[2], s[2];
for(int i = 0; i < 2; i++) {
s[i] = a->size[i] + b->size[i];
p[i] = a->pos[i] - b->pos[i];
}
*minx = p[0] - s[0];
*maxx = p[0] + s[0];
*miny = p[1] - s[1];
*maxy = p[1] + s[1];
}
void
enqcoll(EntityCollision *c)
{
if(ecollsi >= 2048)
return;
ecollsi++;
ecoll[ecollend++] = *c;
if(ecollend >= 2048)
ecollend = 0;
}
EntityCollision *
deqcoll(void)
{
EntityCollision *c;
if(ecollsi <= 0)
return NULL;
ecollsi--;
c = ecoll + ecollstart++;
if(ecollstart >= 2048)
ecollstart = 0;
return c;
}
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