250 lines
5.2 KiB
C
250 lines
5.2 KiB
C
#include <u.h>
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#include <libc.h>
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#include <draw.h>
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#include <event.h>
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enum {
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Kdel = 0x7f
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};
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int N = 49,
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pathlen = 1000,
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nosnake;
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double dt = 0.01,
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xmin = -40,
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xmax = 40,
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ymin = -40,
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ymax = 40,
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v0 = 0.1;
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#define mini(a,b) (((a)<(b))?(a):(b))
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typedef struct Particle Particle;
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struct Particle {
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double x, y;
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double vx, vy;
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double ax, ay;
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double prevx, prevy;
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Image* col;
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};
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typedef struct Path Path;
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struct Path {
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int *x, *y;
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};
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int colors[] = {
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DBlack,
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DRed,
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DGreen,
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DBlue,
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DCyan,
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DMagenta,
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DDarkyellow,
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DDarkgreen,
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DPalegreen,
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DMedgreen,
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DDarkblue,
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DPalebluegreen,
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DPaleblue,
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DBluegreen,
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DGreygreen,
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DPalegreygreen,
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DYellowgreen,
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DMedblue,
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DGreyblue,
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DPalegreyblue,
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DPurpleblue
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};
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Particle *A, *B;
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Particle *prev, *cur;
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Path *paths;
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void
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reset(void)
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{
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int j, grid = sqrt(N)+0.5;
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Particle *p;
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draw(screen, screen->r, display->white, 0, ZP);
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for(j=0;j<N;j++) {
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p = prev+j;
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p->x = 2*(j%grid)+frand()/2;
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p->y = 2*(j/grid)+frand()/2;
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p->vx = 1.*v0*frand();
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p->vy = 1.*v0*frand();
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p->prevx = p->x - p->vx * dt;
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p->prevy = p->y - p->vy * dt;
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p->col = allocimage(display, Rect(0,0,1,1), screen->chan, 1, colors[rand()%(sizeof(colors)/sizeof(int))]);
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if(!p->col) sysfatal("allocimage");
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}
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}
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void
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reverse(void)
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{
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Particle *p, *q;
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Path *pa;
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int i;
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draw(screen, screen->r, display->white, 0, ZP);
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for(i=0;i<N;i++){
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pa=paths+i;
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memset(pa->x, 0, sizeof(int) * pathlen);
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memset(pa->y, 0, sizeof(int) * pathlen);
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p=prev+i;
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q=cur+i;
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p->vx = -q->vx;
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p->vy = -q->vy;
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p->prevx = p->x;
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p->prevy = p->y;
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p->x = q->x;
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p->y = q->y;
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}
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}
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void
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drawpath(Path *p, Image *col, int i)
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{
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int j;
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if((j = i+1) == pathlen)
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j = 0;
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draw(screen, Rect(p->x[i], p->y[i], p->x[i]+1, p->y[i]+1), col, 0, ZP);
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if(nosnake)
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return;
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draw(screen, Rect(p->x[j], p->y[j], p->x[j]+1, p->y[j]+1), display->white, 0, ZP);
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}
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void
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usage(void)
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{
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print("USAGE: mole options\n");
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print(" -N number of particles [49]\n");
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print(" -x left boundary [-40]\n");
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print(" -X right boundary [40]\n");
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print(" -y top boundary [-40]\n");
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print(" -Y bottom boundary [40]\n");
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print(" -t time step [0.01]\n");
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print(" -v maximum start velocity [0.1]\n");
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print(" -P path length [1000]\n");
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exits("usage");
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}
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void
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main(int argc, char** argv)
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{
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int i, j;
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Particle *p, *q;
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Path *pa;
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double dx, dx1, dx2, dy, dy1, dy2, R, F;
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char* f;
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#define FARG(c, v) case c: if(!(f=ARGF())) usage(); v = atof(f); break;
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ARGBEGIN {
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case 'N': if(!(f=ARGF())) usage(); N = atoi(f); break;
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case 'P': if(!(f=ARGF())) usage(); pathlen = atoi(f); break;
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FARG('v', v0);
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FARG('x', xmin);
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FARG('X', xmax);
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FARG('y', ymin);
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FARG('Y', ymax);
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FARG('t', dt);
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default: usage();
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} ARGEND;
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if(pathlen == 0) {
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nosnake = 1;
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pathlen = 1000;
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}
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A = calloc(sizeof(Particle), N);
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B = calloc(sizeof(Particle), N);
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paths = calloc(sizeof(Path), N);
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for(pa=paths;pa<paths+N;pa++){
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pa->x = calloc(sizeof(int), pathlen);
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pa->y = calloc(sizeof(int), pathlen);
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}
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prev = A;
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cur = B;
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srand(time(0));
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initdraw(0, 0, "Molecular Dynamics");
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einit(Emouse | Ekeyboard);
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reset();
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for(i=0;; i++) {
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if(i == pathlen)
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i = 0;
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memset(cur, 0, sizeof(Particle) * N);
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for(p=prev;p<prev+N;p++) {
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for(q=prev;q<p;q++) {
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dx1 = fabs(p->x - q->x);
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dx2 = xmax - xmin - dx1;
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dx = mini(dx1, dx2);
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dy1 = fabs(p->y - q->y);
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dy2 = ymax - ymin - dy1;
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dy = mini(dy1, dy2);
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R = dx*dx + dy*dy;
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if(R >= 9) continue;
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R = 1/sqrt(R);
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double R2, R4, R6, R12;
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R2 = R * R;
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R4 = R2 * R2;
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R6 = R4 * R2;
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R12 = R6 * R6;
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F = 24*(2*R12 - R6);
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if(p->x < q->x) dx = -dx;
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if(p->y < q->y) dy = -dy;
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if(dx1 > dx2) dx = -dx;
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if(dy1 > dy2) dy = -dy;
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dx *= F;
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dy *= F;
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(p-prev+cur)->ax += dx;
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(p-prev+cur)->ay += dy;
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(q-prev+cur)->ax -= dx;
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(q-prev+cur)->ay -= dy;
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}
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}
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for(j=0;j<N;j++) {
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pa = paths+j;
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p = prev+j;
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q = cur+j;
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q->x = 2*p->x - p->prevx + q->ax * dt*dt;
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q->y = 2*p->y - p->prevy + q->ay * dt*dt;
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q->vx = (q->x - p->prevx) / (2*dt);
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q->vy = (q->y - p->prevy) / (2*dt);
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q->prevx = p->x;
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q->prevy = p->y;
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if(q->x > xmax) {q->x -= xmax - xmin; q->prevx -= xmax - xmin;}
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if(q->x < xmin) {q->x += xmax - xmin; q->prevx += xmax - xmin;}
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if(q->y > ymax) {q->y -= ymax - ymin; q->prevy -= ymax - ymin;}
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if(q->y < ymin) {q->y += ymax - ymin; q->prevy += ymax - ymin;}
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q->col = p->col;
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pa->x[i] = (screen->r.max.x - screen->r.min.x) * (q->x - xmin) / (xmax - xmin) + screen->r.min.x;
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pa->y[i] = (screen->r.max.y - screen->r.min.y) * (q->y - ymin) / (ymax - ymin) + screen->r.min.y;
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drawpath(pa, p->col, i);
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}
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Particle* tmp = prev;
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prev = cur;
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cur = tmp;
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flushimage(display, 1);
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if(ecankbd()) {
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switch(ekbd()) {
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case 'q': case Kdel: exits(0); break;
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case 'r': reset(); break;
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case 'R': reverse(); break;
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case 'f': draw(screen, screen->r, display->white, 0, ZP); break;
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}
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}
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}
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}
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void
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eresized(int new)
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{
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if(new) getwindow(display, Refnone);
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}
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