diff options
| -rw-r--r-- | dat.h | 6 | ||||
| -rw-r--r-- | main.c | 38 |
2 files changed, 31 insertions, 13 deletions
@@ -1,4 +1,6 @@ -#define Eg 9.81 +#define Eg 9.81 /* earth's gravity (m·s⁻²) */ +#define Cd 0.45 /* drag coefficient for a sphere */ +#define ρ 1.293 /* air density (kg·m⁻³) */ #define PIX2M 0.001 #define M2PIX (1.0/PIX2M) @@ -6,6 +8,7 @@ enum { Stheta = 0, Spos, Svel, + Sdrag, Sdeltax, Seta, SLEN, @@ -17,4 +20,5 @@ struct Projectile { Point2 p, v; double mass; + double r; }; @@ -15,6 +15,7 @@ RFrame worldrf; Projectile ball; double t0, Δt; double v0; +double A; /* area of the projectile that meets the air */ Point2 target; char stats[SLEN][64]; @@ -47,11 +48,27 @@ fromscreen(Point p) } void +∫(double Δt) +{ + Point2 Fd; /* drag force */ + + Fd = mulpt2(mulpt2(ball.v, -vec2len(ball.v)), 0.5 * Cd*ρ*A); /* ½CdρAv² */ + ball.v = addpt2(ball.v, mulpt2(addpt2(Vec2(0,-Eg), divpt2(Fd, ball.mass)), Δt)); + ball.p = addpt2(ball.p, mulpt2(ball.v, Δt)); + snprint(stats[Spos], sizeof(stats[Spos]), "p: %v", ball.p); + snprint(stats[Sdrag], sizeof(stats[Sdrag]), "Fd: %v", Fd); + if(ball.p.y <= (2+1)*M2PIX){ + ball.p.y = (2+1)*M2PIX; + ball.v = Vec2(0,0); + } +} + +void drawstats(void) { int i; - snprint(stats[Svel], sizeof(stats[Svel]), "v: %gm/s", vec2len(ball.v)); + snprint(stats[Svel], sizeof(stats[Svel]), "|v|: %gm/s", vec2len(ball.v)); snprint(stats[Sdeltax], sizeof(stats[Sdeltax]), "Δx: %gm", target.x-ball.p.x); for(i = 0; i < nelem(stats); i++) stringn(screen, addpt(screen->r.min, Pt(10, font->height*i+1)), statc, ZP, font, stats[i], sizeof(stats[i])); @@ -86,7 +103,8 @@ mmb(void) switch(menuhit(2, mc, &menu, nil)){ case SETV0: enter("v0(m/s):", buf, sizeof(buf), mc, kc, nil); - v0 = strtod(buf, 0); + if(buf[0] != 0) + v0 = strtod(buf, nil); break; } } @@ -124,7 +142,7 @@ mouse(void) if(ball.p.y <= (2+1)*M2PIX){ p = subpt2(fromscreen(mc->xy), ball.p); θ = atan2(p.y, p.x); - snprint(stats[Stheta], sizeof(stats[Stheta]), "θ: %g°", θ*180/PI); + snprint(stats[Stheta], sizeof(stats[Stheta]), "θ: %g°", θ/DEG); dist = v0*v0*sin(2*θ)/Eg; target = Pt2(ball.p.x+dist, 0, 1); eta = 2*v0*sin(θ)/Eg; @@ -204,6 +222,8 @@ threadmain(int argc, char *argv[]) ball.p = Pt2((2+1)*M2PIX,(2+1)*M2PIX,1); ball.v = Vec2(0, 0); ball.mass = 106000; + ball.r = 0.1; /* 10cm */ + A = 2*PI*ball.r*ball.r; /* ½(4πr²) */ v0 = 1640; /* Paris Gun's specs */ scrsync = chancreate(1, 0); @@ -227,14 +247,8 @@ threadmain(int argc, char *argv[]) case 2: key(r); break; case 3: redraw(); break; } - Δt = (nsec()-t0)/1e9; - ball.v = addpt2(ball.v, mulpt2(Vec2(0,-Eg), Δt)); - ball.p = addpt2(ball.p, mulpt2(ball.v, Δt)); - snprint(stats[Spos], sizeof(stats[Spos]), "p: %v", ball.p); - if(ball.p.y <= (2+1)*M2PIX){ - ball.p.y = (2+1)*M2PIX; - ball.v = Vec2(0,0); - } - t0 += Δt*1e9; + Δt = (nsec()-t0); + ∫(Δt/1e9); + t0 += Δt; } } |