verlet integrator now respects node mass

Author: samizdatco

src/physics/physics.js

@@ -293,7 +293,7 @@
           if (that.integrator=='euler'){
             point.v = point.v.add(point.f.multiply(timestep)).multiply(1-that.friction);
           }else{
-            point.v = point.v.add(point.f.add(point._F).multiply(timestep*0.5)).multiply(1-that.friction);
+            point.v = point.v.add(point.f.add(point._F.divide(point._m)).multiply(timestep*0.5)).multiply(1-that.friction);
           }
           point.f.x = point.f.y = 0
 
@@ -323,8 +323,8 @@
           }else{
             //this should follow the equation
             //x(t+1) = x(t) + v(t) * timestep + 1/2 * timestep^2 * a(t)
-            var accelPart = point.f.multiply(0.5 * timestep * timestep);
-            point.p = point.p.add(point.v.multiply(timestep)).add(accelPart);
+            var accel = point.f.multiply(0.5 * timestep * timestep).divide(point.m);
+            point.p = point.p.add(point.v.multiply(timestep)).add(accel);
           }
 
           if (!bottomright){