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authorrodri <rgl@antares-labs.eu>2021-03-06 17:11:47 +0000
committerrodri <rgl@antares-labs.eu>2021-03-06 17:11:47 +0000
commit5ecc14e07c5dcc40e418f450f0c34dceb7f7e326 (patch)
treed916d6934cc119c192cae31d6b791d8b94e14421
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implemented three integrators and a simple time stepping model.
-rw-r--r--alloc.c44
-rw-r--r--dat.h14
-rw-r--r--fns.h3
-rw-r--r--main.c285
-rw-r--r--mkfile27
-rw-r--r--readme.md3
6 files changed, 376 insertions, 0 deletions
diff --git a/alloc.c b/alloc.c
new file mode 100644
index 0000000..2589e89
--- /dev/null
+++ b/alloc.c
@@ -0,0 +1,44 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+
+void*
+emalloc(ulong n)
+{
+ void *p;
+
+ p = malloc(n);
+ if(p == nil)
+ sysfatal("malloc: %r");
+ setmalloctag(p, getcallerpc(&n));
+ return p;
+}
+
+void*
+erealloc(void *p, ulong n)
+{
+ void *np;
+
+ np = realloc(p, n);
+ if(np == nil){
+ if(n == 0)
+ return nil;
+ sysfatal("realloc: %r");
+ }
+ if(p == nil)
+ setmalloctag(np, getcallerpc(&p));
+ else
+ setrealloctag(np, getcallerpc(&p));
+ return np;
+}
+
+Image*
+eallocimage(Display *d, Rectangle r, ulong chan, int repl, ulong col)
+{
+ Image *i;
+
+ i = allocimage(d, r, chan, repl, col);
+ if(i == nil)
+ sysfatal("allocimage: %r");
+ return i;
+}
diff --git a/dat.h b/dat.h
new file mode 100644
index 0000000..6503042
--- /dev/null
+++ b/dat.h
@@ -0,0 +1,14 @@
+typedef struct State State;
+typedef struct Derivative Derivative;
+
+struct State
+{
+ double x, v;
+ double acc, min, max, avg;
+ int nsteps;
+};
+
+struct Derivative
+{
+ double dx, dv;
+};
diff --git a/fns.h b/fns.h
new file mode 100644
index 0000000..ece9b68
--- /dev/null
+++ b/fns.h
@@ -0,0 +1,3 @@
+void *emalloc(ulong);
+void *erealloc(void*, ulong);
+Image *eallocimage(Display*, Rectangle, ulong, int, ulong);
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..420bc72
--- /dev/null
+++ b/main.c
@@ -0,0 +1,285 @@
+#include <u.h>
+#include <libc.h>
+#include <thread.h>
+#include <draw.h>
+#include <mouse.h>
+#include <keyboard.h>
+#include <geometry.h>
+#include "dat.h"
+#include "fns.h"
+
+RFrame screenrf;
+State state;
+double timestep;
+
+
+double min(double a, double b) { return a < b? a: b; }
+double max(double a, double b) { return a > b? a: b; }
+
+/*
+ * Dynamics stepper
+ *
+ * Currently set to a basic spring-damper system.
+ */
+double
+accel(State *s, double t)
+{
+ static double k = 15, b = 0.1;
+
+ USED(t);
+ return -k*s->x - b*s->v;
+}
+
+Derivative
+eval(State *s0, double t, double Δt, Derivative *d)
+{
+ State s;
+ Derivative res;
+
+ s.x = s0->x + d->dx*Δt;
+ s.v = s0->v + d->dv*Δt;
+
+ res.dx = s.v;
+ res.dv = accel(&s, t+Δt);
+ return res;
+}
+
+/*
+ * Explicit Euler Integrator
+ */
+void
+euler0(State *s, double t, double Δt)
+{
+ static Derivative ZD = {0,0};
+ Derivative d;
+
+ d = eval(s, t, Δt, &ZD);
+
+ s->x += d.dx*Δt;
+ s->v += d.dv*Δt;
+}
+
+/*
+ * Semi-implicit Euler Integrator
+ */
+void
+euler1(State *s, double t, double Δt)
+{
+ static Derivative ZD = {0,0};
+ Derivative d;
+
+ d = eval(s, t, Δt, &ZD);
+
+ s->v += d.dv*Δt;
+ s->x += s->v*Δt;
+}
+
+/*
+ * RK4 Integrator
+ */
+void
+rk4(State *s, double t, double Δt)
+{
+ static Derivative ZD = {0,0};
+ Derivative a, b, c, d;
+ double dxdt, dvdt;
+
+ a = eval(s, t, 0, &ZD);
+ b = eval(s, t, Δt/2, &a);
+ c = eval(s, t, Δt/2, &b);
+ d = eval(s, t, Δt, &c);
+
+ dxdt = 1.0/6 * (a.dx + 2*(b.dx + c.dx) + d.dx);
+ dvdt = 1.0/6 * (a.dv + 2*(b.dv + c.dv) + d.dv);
+
+ s->x += dxdt*Δt;
+ s->v += dvdt*Δt;
+}
+
+/*
+ * The Integrator
+ */
+void
+integrate(State *s, double t, double Δt)
+{
+ //euler0(s, t, Δt);
+ //euler1(s, t, Δt);
+ rk4(s, t, Δt);
+}
+
+Point
+toscreen(Point2 p)
+{
+ p = invrframexform(p, screenrf);
+ return Pt(p.x,p.y);
+}
+
+Point2
+fromscreen(Point p)
+{
+ return rframexform(Pt2(p.x,p.y,1), screenrf);
+}
+
+void
+drawtimestep(double t)
+{
+ char buf[32];
+
+ snprint(buf, sizeof buf, "t=%gs", t);
+ string(screen, addpt(screen->r.min, Pt(10,10)), display->white, ZP, font, buf);
+}
+
+void
+drawbar(double v)
+{
+ struct {
+ Point2 p0, p1;
+ } l = {
+ Pt2(-2,v,1),
+ Pt2(2,v,1)
+ };
+ char buf[32];
+
+ line(screen, toscreen(l.p0), toscreen(l.p1), 0, 0, 0, display->white, ZP);
+ snprint(buf, sizeof buf, "%.3f", v);
+ l.p1.x += 10;
+ string(screen, toscreen(l.p1), display->white, ZP, font, buf);
+}
+
+void
+redraw(void)
+{
+ lockdisplay(display);
+
+ draw(screen, screen->r, display->black, nil, ZP);
+ drawtimestep(timestep);
+ drawbar(state.min); drawbar(state.max); drawbar(state.avg);
+ fillellipse(screen, toscreen(Pt2(0,state.x,1)), 2, 2, display->white, ZP);
+
+ flushimage(display, 1);
+ unlockdisplay(display);
+}
+
+void
+resized(void)
+{
+ lockdisplay(display);
+ if(getwindow(display, Refnone) < 0)
+ sysfatal("resize failed");
+ unlockdisplay(display);
+ screenrf.p = Pt2(screen->r.min.x+Dx(screen->r)/2,screen->r.max.y-Dy(screen->r)/2,1);
+ redraw();
+}
+
+void
+rmb(Mousectl *mc)
+{
+ enum {
+ RESET,
+ };
+ static char *items[] = {
+ [RESET] "reset",
+ nil
+ };
+ static Menu menu = { .item = items };
+
+ switch(menuhit(3, mc, &menu, _screen)){
+ case RESET:
+ //resetsim();
+ break;
+ }
+}
+
+void
+mouse(Mousectl *mc, Keyboardctl *)
+{
+ if((mc->buttons & 4) != 0)
+ rmb(mc);
+}
+
+void
+key(Rune r)
+{
+ switch(r){
+ case Kdel:
+ case 'q':
+ threadexitsall(nil);
+ }
+}
+
+void
+usage(void)
+{
+ fprint(2, "usage: %s\n", argv0);
+ exits("usage");
+}
+
+void
+threadmain(int argc, char *argv[])
+{
+ Mousectl *mc;
+ Keyboardctl *kc;
+ Rune r;
+ double t, Δt;
+
+ ARGBEGIN{
+ default: usage();
+ }ARGEND;
+ if(argc > 0)
+ usage();
+
+ if(initdraw(nil, nil, nil) < 0)
+ sysfatal("initdraw: %r");
+ if((mc = initmouse(nil, screen)) == nil)
+ sysfatal("initmouse: %r");
+ if((kc = initkeyboard(nil)) == nil)
+ sysfatal("initkeyboard: %r");
+ screenrf.p = Pt2(screen->r.min.x+Dx(screen->r)/2,screen->r.max.y-Dy(screen->r)/2,1);
+ screenrf.bx = Vec2(1, 0);
+ screenrf.by = Vec2(0,-1);
+
+ t = 0;
+ Δt = 0.01;
+ state.x = 100;
+ state.v = 0;
+
+ display->locking = 1;
+ unlockdisplay(display);
+ redraw();
+
+ for(;;){
+ enum { MOUSE, RESIZE, KEYBOARD };
+ Alt a[] = {
+ {mc->c, &mc->Mouse, CHANRCV},
+ {mc->resizec, nil, CHANRCV},
+ {kc->c, &r, CHANRCV},
+ {nil, nil, CHANNOBLK}
+ };
+
+ switch(alt(a)){
+ case MOUSE:
+ mouse(mc, kc);
+ break;
+ case RESIZE:
+ resized();
+ break;
+ case KEYBOARD:
+ key(r);
+ break;
+ }
+
+ integrate(&state, t, Δt);
+
+ state.acc += state.x;
+ state.avg = state.acc/++state.nsteps;
+ state.min = min(state.min, state.x);
+ state.max = max(state.max, state.x);
+
+ redraw();
+
+ t += Δt;
+ timestep = t;
+
+ sleep(66);
+ }
+}
diff --git a/mkfile b/mkfile
new file mode 100644
index 0000000..5c8fdf6
--- /dev/null
+++ b/mkfile
@@ -0,0 +1,27 @@
+</$objtype/mkfile
+
+BIN=/$objtype/bin/games
+TARG=physics
+OFILES=\
+ alloc.$O\
+ main.$O\
+
+HFILES=\
+ dat.h\
+ fns.h\
+ libgeometry/geometry.h\
+
+LIB=\
+ libgeometry/libgeometry.a$O\
+
+CFLAGS=$CFLAGS -Ilibgeometry
+
+</sys/src/cmd/mkone
+
+libgeometry/libgeometry.a$O:
+ cd libgeometry
+ mk install
+
+clean nuke:V:
+ rm -f *.[$OS] [$OS].??* $TARG
+ @{cd libgeometry; mk $target}
diff --git a/readme.md b/readme.md
new file mode 100644
index 0000000..2e6f38a
--- /dev/null
+++ b/readme.md
@@ -0,0 +1,3 @@
+# Game Physics
+
+Applied concepts from the awesome [Gaffer On Games](https://gafferongames.com/).