/// <summary>
/// Initialize the simulation with the provided enclosing simulation. After
/// this call has been made, the simulation can be queried for the
/// n-body force acting on a given item.
/// </summary>
/// <param name="fsim">the encompassing ForceSimulator</param>
public override void Init(ForceSimulator fsim)
{
clear(); // clear internal state
// compute and squarify bounds of quadtree
float x1 = float.MaxValue, y1 = float.MaxValue;
float x2 = float.MinValue, y2 = float.MinValue;
foreach (ForceItem item in fsim.Items)
{
float x = item.Location[0];
float y = item.Location[1];
if (x < x1)
{
x1 = x;
}
if (y < y1)
{
y1 = y;
}
if (x > x2)
{
x2 = x;
}
if (y > y2)
{
y2 = y;
}
}
float dx = x2 - x1, dy = y2 - y1;
if (dx > dy)
{
y2 = y1 + dx;
}
else
{
x2 = x1 + dy;
}
setBounds(x1, y1, x2, y2);
// Insert items into quadtree
foreach (ForceItem item in fsim.Items)
{
Insert(item);
}
// calculate magnitudes and centers of mass
CalculateMass(root);
}
/// <summary>
/// Initialize this force function. This default implementation does nothing.
/// Subclasses should override this method with any needed initialization.
/// </summary>
/// <param name="fsim">the encompassing ForceSimulator</param>
public virtual void Init(ForceSimulator fsim)
{
// do nothing.
}
/// <summary>
/// Integrates the specified simulation.
/// </summary>
/// <param name="sim">The sim.</param>
/// <param name="timestep">The timestep.</param>
public void Integrate(ForceSimulator sim, long timestep)
{
float speedLimit = sim.SpeedLimit;
float vx, vy, v, coeff;
float[,] k, l;
foreach (ForceItem item in sim.Items)
{
coeff = timestep / item.Mass;
k = item.RungeKuttaTemp1;
l = item.RungeKuttaTemp2;
item.PreviousLocation[0] = item.Location[0];
item.PreviousLocation[1] = item.Location[1];
k[0, 0] = timestep * item.Velocity[0];
k[0, 1] = timestep * item.Velocity[1];
l[0, 0] = coeff * item.Force[0];
l[0, 1] = coeff * item.Force[1];
// Set the position to the new predicted position
item.Location[0] += 0.5f * k[0, 0];
item.Location[1] += 0.5f * k[0, 1];
}
// recalculate forces
sim.Accumulate();
foreach (ForceItem item in sim.Items)
{
coeff = timestep / item.Mass;
k = item.RungeKuttaTemp1;
l = item.RungeKuttaTemp2;
vx = item.Velocity[0] + .5f * l[0, 0];
vy = item.Velocity[1] + .5f * l[0, 1];
v = (float)Math.Sqrt(vx * vx + vy * vy);
if (v > speedLimit)
{
vx = speedLimit * vx / v;
vy = speedLimit * vy / v;
}
k[1, 0] = timestep * vx;
k[1, 1] = timestep * vy;
l[1, 0] = coeff * item.Force[0];
l[1, 1] = coeff * item.Force[1];
// Set the position to the new predicted position
item.Location[0] = item.PreviousLocation[0] + 0.5f * k[1, 0];
item.Location[1] = item.PreviousLocation[1] + 0.5f * k[1, 1];
}
// recalculate forces
sim.Accumulate();
foreach (ForceItem item in sim.Items)
{
coeff = timestep / item.Mass;
k = item.RungeKuttaTemp1;
l = item.RungeKuttaTemp2;
vx = item.Velocity[0] + .5f * l[1, 0];
vy = item.Velocity[1] + .5f * l[1, 1];
v = (float)Math.Sqrt(vx * vx + vy * vy);
if (v > speedLimit)
{
vx = speedLimit * vx / v;
vy = speedLimit * vy / v;
}
k[2, 0] = timestep * vx;
k[2, 1] = timestep * vy;
l[2, 0] = coeff * item.Force[0];
l[2, 1] = coeff * item.Force[1];
// Set the position to the new predicted position
item.Location[0] = item.PreviousLocation[0] + 0.5f * k[2, 0];
item.Location[1] = item.PreviousLocation[1] + 0.5f * k[2, 1];
}
// recalculate forces
sim.Accumulate();
foreach (ForceItem item in sim.Items)
{
coeff = timestep / item.Mass;
k = item.RungeKuttaTemp1;
l = item.RungeKuttaTemp2;
float[] p = item.PreviousLocation;
vx = item.Velocity[0] + l[2, 0];
vy = item.Velocity[1] + l[2, 1];
v = (float)Math.Sqrt(vx * vx + vy * vy);
if (v > speedLimit)
{
vx = speedLimit * vx / v;
vy = speedLimit * vy / v;
}
k[3, 0] = timestep * vx;
k[3, 1] = timestep * vy;
l[3, 0] = coeff * item.Force[0];
l[3, 1] = coeff * item.Force[1];
item.Location[0] = p[0] + (k[0, 0] + k[3, 0]) / 6.0f + (k[1, 0] + k[2, 0]) / 3.0f;
item.Location[1] = p[1] + (k[0, 1] + k[3, 1]) / 6.0f + (k[1, 1] + k[2, 1]) / 3.0f;
vx = (l[0, 0] + l[3, 0]) / 6.0f + (l[1, 0] + l[2, 0]) / 3.0f;
vy = (l[0, 1] + l[3, 1]) / 6.0f + (l[1, 1] + l[2, 1]) / 3.0f;
v = (float)Math.Sqrt(vx * vx + vy * vy);
if (v > speedLimit)
{
vx = speedLimit * vx / v;
vy = speedLimit * vy / v;
}
item.Velocity[0] += vx;
item.Velocity[1] += vy;
}
}
