ref: d1a80cdf7a322e572a024bf3f902eab34d51d7e7
dir: /path.c/
#include <u.h>
#include <libc.h>
#include <draw.h>
#include "dat.h"
#include "fns.h"
/* jump point search with block-based symmetry breaking (JPS(B): 2014, harabor and
* grastien), using pairing heaps for priority queues and a bitmap representing the
* entire map.
* no preprocessing since we'd have to repair the database each time anything moves,
* which is a pain.
* no pruning of intermediate nodes (JPS(B+P)) as of yet, until other options are
* assessed.
* the pruning rules adhere to (2012, harabor and grastien) to disallow corner cutting
* in diagonal movement, and movement code elsewhere reflects that.
* if there is no path to the target, the unit still has to move to the nearest
* accessible node. if there is such a node, we first attempt to find a nearer
* non-jump point in a cardinal direction, and if successful, the point is added at
* the end of the path. unlike plain a∗, we cannot rely on the path backtracked from
* the nearest node, since it is no longer guaranteed to be optimal, and will in fact
* go all over the place. unless jump points can be connected to all other visible
* jump points so as to perform a search on this reduced graph without rediscovering
* the map, we're forced to re-do pathfinding to this nearest node. the search should
* be much quicker since this new node is accessible.
* pathfinding is not limited to an area, so entire map may be scanned, which is too
* slow. simple approaches don't seem to work well, it would perhaps be better to
* only consider a sub-grid of the map, but the data structures currently used do not
* allow it. since the pathfinding algorithm will probably change, the current
* implementation disregards the issue.
* pathfinding is limited by number of moves (the cost function). this prevents the
* search to look at the entire map, but also means potentially non-optimal paths and
* more pathfinding when crossing the boundaries.
* since units are bigger than the pathfinding grid, the grid is "compressed" when
* scanned by using a sliding window the size of the unit, so the rest of the algorithm
* still operates on 3x3 neighbor grids, with each bit checking as many nodes as needed
* for impassibility. such an approach has apparently not been discussed in regards
* to JPS(B), possibly since JPS(B) is a particular optimization of the original
* algorithm and this snag may rarely be hit in practice.
* map dimensions are assumed to be multiples of 16 tiles.
* the code is currently horrendously ugly, though short, and ultimately wrong.
* movement should occur at any angle (rather than in 8 directions) and unit sizes
* do not have a common denominator higher than 1 pixel. */
enum{
θ∅ = 0,
θN,
θE,
θS,
θW,
θNE,
θSE,
θSW,
θNW,
};
#define SQRT2 1.4142135623730951
static Pairheap *queue;
static Node *nearest;
static void
clearpath(void)
{
nukequeue(&queue);
memset(nodemap, 0, nodemapwidth * nodemapheight * sizeof *nodemap);
nearest = nil;
}
int
isblocked(int x, int y, Obj *o)
{
u64int *row;
row = bload(x, y, o->w, o->h, 0, 0, 0, 0);
return (*row & 1ULL << 63) != 0;
}
void
markmobj(Mobj *mo, int set)
{
int w, h;
w = mo->o->w;
if((mo->subpx & Subpxmask) != 0 && mo->x != (mo->px + 1) / Nodewidth)
w++;
h = mo->o->h;
if((mo->subpy & Subpxmask) != 0 && mo->y != (mo->py + 1) / Nodewidth)
h++;
bset(mo->x, mo->y, w, h, set);
}
static double
octdist(Node *a, Node *b)
{
int dx, dy;
dx = abs(a->x - b->x);
dy = abs(a->y - b->y);
return 1 * (dx + dy) + (SQRT2 - 2 * 1) * min(dx, dy);
}
/* FIXME: horrendous. use fucking tables you moron */
static Node *
jumpeast(int x, int y, int w, int h, Node *b, int *ofs, int left, int rot)
{
int nbits, steps, stop, end, *u, *v, ss, Δu, Δug, Δug2, Δvg;
u64int bs, *row;
Node *n;
if(rot){
u = &y;
v = &x;
Δug = b->y - y;
Δvg = b->x - x;
}else{
u = &x;
v = &y;
Δug = b->x - x;
Δvg = b->y - y;
}
steps = 0;
nbits = 64 - w + 1;
ss = left ? -1 : 1;
(*v)--;
for(;;){
row = bload(x, y, w, h, 0, 2, left, rot);
bs = row[1];
if(left){
bs |= row[0] << 1 & ~row[0];
bs |= row[2] << 1 & ~row[2];
}else{
bs |= row[0] >> 1 & ~row[0];
bs |= row[2] >> 1 & ~row[2];
}
if(bs)
break;
(*u) += ss * nbits;
steps += nbits;
}
if(left){
stop = lsb(bs);
Δu = stop;
}else{
stop = msb(bs);
Δu = 63 - stop;
}
end = (row[1] & 1ULL << stop) != 0;
(*u) += ss * Δu;
(*v)++;
steps += Δu;
Δug2 = rot ? b->y - y : b->x - x;
if(ofs != nil)
*ofs = steps;
if(end && Δug2 == 0)
return nil;
if(Δvg == 0 && (Δug == 0 || (Δug < 0) ^ (Δug2 < 0))){
b->Δg = steps - abs(Δug2);
b->Δlen = b->Δg;
return b;
}
if(end)
return nil;
assert(x < nodemapwidth && y < nodemapheight);
n = nodemap + y * nodemapwidth + x;
n->x = x;
n->y = y;
n->Δg = steps;
n->Δlen = steps;
return n;
}
static Node *
jumpdiag(int x, int y, int w, int h, Node *b, int dir)
{
int left1, ofs1, left2, ofs2, Δx, Δy, steps;
Node *n;
steps = 0;
left1 = left2 = Δx = Δy = 0;
switch(dir){
case θNE: left1 = 1; left2 = 0; Δx = 1; Δy = -1; break;
case θSW: left1 = 0; left2 = 1; Δx = -1; Δy = 1; break;
case θNW: left1 = 1; left2 = 1; Δx = -1; Δy = -1; break;
case θSE: left1 = 0; left2 = 0; Δx = 1; Δy = 1; break;
}
for(;;){
steps++;
x += Δx;
y += Δy;
if(*bload(x, y, w, h, 0, 0, 0, 0) & 1ULL << 63)
return nil;
if(jumpeast(x, y, w, h, b, &ofs1, left1, 1) != nil
|| jumpeast(x, y, w, h, b, &ofs2, left2, 0) != nil)
break;
if(ofs1 == 0 || ofs2 == 0)
return nil;
}
assert(x < nodemapwidth && y < nodemapheight);
n = nodemap + y * nodemapwidth + x;
n->x = x;
n->y = y;
n->Δg = steps;
n->Δlen = steps * SQRT2;
return n;
}
static Node *
jump(int x, int y, int w, int h, Node *b, int dir)
{
Node *n;
switch(dir){
case θE: n = jumpeast(x, y, w, h, b, nil, 0, 0); break;
case θW: n = jumpeast(x, y, w, h, b, nil, 1, 0); break;
case θS: n = jumpeast(x, y, w, h, b, nil, 0, 1); break;
case θN: n = jumpeast(x, y, w, h, b, nil, 1, 1); break;
default: n = jumpdiag(x, y, w, h, b, dir); break;
}
return n;
}
/* 2012, harabor and grastien: disabling corner cutting implies that only moves in
* a cardinal direction may produce forced neighbors */
static int
forced(int n, int dir)
{
int m;
m = 0;
switch(dir){
case θN:
if((n & (1<<8 | 1<<5)) == 1<<8) m |= 1<<5 | 1<<2;
if((n & (1<<6 | 1<<3)) == 1<<6) m |= 1<<3 | 1<<0;
break;
case θE:
if((n & (1<<2 | 1<<1)) == 1<<2) m |= 1<<1 | 1<<0;
if((n & (1<<8 | 1<<7)) == 1<<8) m |= 1<<7 | 1<<6;
break;
case θS:
if((n & (1<<2 | 1<<5)) == 1<<2) m |= 1<<5 | 1<<8;
if((n & (1<<0 | 1<<3)) == 1<<0) m |= 1<<3 | 1<<6;
break;
case θW:
if((n & (1<<0 | 1<<1)) == 1<<0) m |= 1<<1 | 1<<2;
if((n & (1<<6 | 1<<7)) == 1<<6) m |= 1<<7 | 1<<8;
break;
}
return m;
}
static int
natural(int n, int dir)
{
int m;
switch(dir){
/* disallow corner coasting on the very first move */
default:
if((n & (1<<1 | 1<<3)) != 0)
n |= 1<<0;
if((n & (1<<7 | 1<<3)) != 0)
n |= 1<<6;
if((n & (1<<7 | 1<<5)) != 0)
n |= 1<<8;
if((n & (1<<1 | 1<<5)) != 0)
n |= 1<<2;
return n;
case θN: return n | ~(1<<1);
case θE: return n | ~(1<<3);
case θS: return n | ~(1<<7);
case θW: return n | ~(1<<5);
case θNE: m = 1<<1 | 1<<3; return (n & m) == 0 ? n | ~(1<<0 | m) : n | 1<<0;
case θSE: m = 1<<7 | 1<<3; return (n & m) == 0 ? n | ~(1<<6 | m) : n | 1<<6;
case θSW: m = 1<<7 | 1<<5; return (n & m) == 0 ? n | ~(1<<8 | m) : n | 1<<8;
case θNW: m = 1<<1 | 1<<5; return (n & m) == 0 ? n | ~(1<<2 | m) : n | 1<<2;
}
}
static int
prune(int n, int dir)
{
return natural(n, dir) & ~forced(n, dir);
}
static int
neighbors(int x, int y, int w, int h)
{
u64int *row;
row = bload(x-1, y-1, w, h, 2, 2, 1, 0);
return (row[2] & 7) << 6 | (row[1] & 7) << 3 | row[0] & 7;
}
static Node **
successors(Node *n, int w, int h, Node *b)
{
static Node *dir[8+1];
static dtab[2*(nelem(dir)-1)]={
1<<1, θN, 1<<3, θE, 1<<7, θS, 1<<5, θW,
1<<0, θNE, 1<<6, θSE, 1<<8, θSW, 1<<2, θNW
};
int i, ns;
Node *s, **p;
ns = neighbors(n->x, n->y, w, h);
ns = prune(ns, n->dir);
memset(dir, 0, sizeof dir);
for(i=0, p=dir; i<nelem(dtab); i+=2){
if(ns & dtab[i])
continue;
if((s = jump(n->x, n->y, w, h, b, dtab[i+1])) != nil){
s->dir = dtab[i+1];
*p++ = s;
}
}
return dir;
}
static Node *
a∗(Node *a, Node *b, Mobj *mo)
{
double g, Δg;
Node *x, *n, **dp;
Pairheap *pn;
if(a == b){
werrstr("a∗: moving in place");
return nil;
}
x = a;
a->h = octdist(a, b);
pushqueue(a, &queue);
while((pn = popqueue(&queue)) != nil){
x = pn->n;
free(pn);
if(x == b)
break;
x->closed = 1;
dp = successors(x, mo->o->w, mo->o->h, b);
for(n=*dp++; n!=nil; n=*dp++){
if(n->closed)
continue;
g = x->g + n->Δg;
Δg = n->g - g;
if(!n->open){
n->from = x;
n->g = g;
n->h = octdist(n, b);
n->len = x->len + n->Δlen;
n->open = 1;
n->step = x->step + 1;
pushqueue(n, &queue);
}else if(Δg > 0){
n->from = x;
n->step = x->step + 1;
n->len = x->len + n->Δlen;
n->g -= Δg;
decreasekey(n->p, Δg, &queue);
}
if(nearest == nil || n->h < nearest->h)
nearest = n;
}
}
return x;
}
static void
backtrack(Node *n, Node *a, Mobj *mo)
{
int x, y;
Point *p;
assert(n != a && n->step > 0);
if(mo->npathbuf < n->step){
mo->paths = erealloc(mo->paths,
n->step * sizeof mo->paths,
mo->npathbuf * sizeof mo->paths);
mo->npathbuf = n->step;
}
mo->pathlen = n->len;
p = mo->paths + n->step;
mo->pathe = p--;
for(; n!=a; n=n->from){
x = n->x * Nodewidth;
y = n->y * Nodeheight;
*p-- = (Point){x, y};
}
assert(p == mo->paths - 1);
}
static Node *
nearestnonjump(Node *n, Node *b, Mobj *mo)
{
static Point dirtab[] = {
{0,-1},
{1,0},
{0,1},
{-1,0},
};
int i, x, y;
Node *m, *min;
min = n;
for(i=0; i<nelem(dirtab); i++){
x = n->x + dirtab[i].x;
y = n->y + dirtab[i].y;
while(!isblocked(x, y, mo->o)){
m = nodemap + y * nodemapwidth + x;
m->x = x;
m->y = y;
m->h = octdist(m, b);
if(min->h < m->h)
break;
min = m;
x += dirtab[i].x;
y += dirtab[i].y;
}
}
if(min != n){
min->from = n;
min->open = 1;
min->step = n->step + 1;
}
return min;
}
void
setgoal(Point *p, Mobj *mo, Mobj *block)
{
int x, y, e;
double Δ, Δ´;
Node *n1, *n2, *pm;
if(block == nil){
mo->goalblocked = 0;
return;
}
mo->goalblocked = 1;
dprint("setgoal: moving goal %d,%d in block %#p ", p->x, p->y, block);
pm = nodemap + p->y * nodemapwidth + p->x;
pm->x = p->x;
pm->y = p->y;
Δ = 0x7ffffff;
x = block->x;
y = block->y;
n1 = nodemap + y * nodemapwidth + x;
n2 = n1 + (block->o->h - 1) * nodemapwidth;
for(e=x+block->o->w; x<e; x++, n1++, n2++){
n1->x = x;
n1->y = y;
Δ´ = octdist(pm, n1);
if(Δ´ < Δ){
Δ = Δ´;
p->x = x;
p->y = y;
}
n2->x = x;
n2->y = y + block->o->h - 1;
Δ´ = octdist(pm, n2);
if(Δ´ < Δ){
Δ = Δ´;
p->x = x;
p->y = y + block->o->h - 1;
}
}
x = block->x;
y = block->y + 1;
n1 = nodemap + y * nodemapwidth + x;
n2 = n1 + block->o->w - 1;
for(e=y+block->o->h-2; y<e; y++, n1+=nodemapwidth, n2+=nodemapwidth){
n1->x = x;
n1->y = y;
Δ´ = octdist(pm, n1);
if(Δ´ < Δ){
Δ = Δ´;
p->x = x;
p->y = y;
}
n2->x = x + block->o->w - 1;
n2->y = y;
Δ´ = octdist(pm, n2);
if(Δ´ < Δ){
Δ = Δ´;
p->x = x + block->o->w - 1;
p->y = y;
}
}
dprint("to %d,%d\n", p->x, p->y);
}
int
findpath(Point p, Mobj *mo)
{
Node *a, *b, *n;
dprint("findpath %d,%d → %d,%d\n", mo->x, mo->y, p.x, p.y);
clearpath();
a = nodemap + mo->y * nodemapwidth + mo->x;
a->x = mo->x;
a->y = mo->y;
b = nodemap + p.y * nodemapwidth + p.x;
b->x = p.x;
b->y = p.y;
markmobj(mo, 0);
n = a∗(a, b, mo);
if(n != b){
dprint("findpath: goal unreachable\n");
if((n = nearest) == a || n == nil || a->h < n->h){
werrstr("a∗: can't move");
markmobj(mo, 1);
return -1;
}
dprint("nearest: %#p %d,%d dist %f\n", n, n->x, n->y, n->h);
b = nearestnonjump(n, b, mo);
if(b == a){
werrstr("a∗: really can't move");
markmobj(mo, 1);
return -1;
}
clearpath();
a->x = mo->x;
a->y = mo->y;
b->x = (b - nodemap) % nodemapwidth;
b->y = (b - nodemap) / nodemapwidth;
if((n = a∗(a, b, mo)) == nil)
sysfatal("findpath: phase error");
}
markmobj(mo, 1);
backtrack(n, a, mo);
return 0;
}