aboutsummaryrefslogtreecommitdiff
path: root/physics.c
diff options
context:
space:
mode:
Diffstat (limited to 'physics.c')
-rw-r--r--physics.c100
1 files changed, 100 insertions, 0 deletions
diff --git a/physics.c b/physics.c
new file mode 100644
index 0000000..5f45fd9
--- /dev/null
+++ b/physics.c
@@ -0,0 +1,100 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+#include "dat.h"
+#include "fns.h"
+
+//enum { DYNTIME, RENTIME, NSTATS };
+//Stats simstats[NSTATS];
+
+
+/*
+ * Dynamics stepper
+ *
+ * Currently set to a basic spring-damper system.
+ */
+static double
+accel(GameState *s, double t)
+{
+ static double k = 15, b = 0.1;
+
+ USED(t);
+ return -k*s->x - b*s->v;
+}
+
+static Derivative
+eval(GameState *s0, double t, double Δt, Derivative *d)
+{
+ GameState 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
+ */
+static void
+euler0(GameState *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
+ */
+static void
+euler1(GameState *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
+ */
+static void
+rk4(GameState *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(GameState *s, double t, double Δt)
+{
+ //euler0(s, t, Δt);
+ //euler1(s, t, Δt);
+ rk4(s, t, Δt);
+}