internal override float ComputeTOI(ref Sweep sweepA, ref Sweep sweepB)
{
TOIInput input;
input.sweepA = sweepA;
input.sweepB = sweepB;
input.tolerance = Settings.b2_linearSlop;
return(TimeOfImpact.CalculateTimeOfImpact(ref input, (PolygonShape)_fixtureA.GetShape(), (CircleShape)_fixtureB.GetShape()));
}
/// Compute the time when two shapes begin to touch or touch at a closer distance.
/// TOI considers the shape radii. It attempts to have the radii overlap by the tolerance.
/// Iterations terminate with the overlap is within 0.5 * tolerance. The tolerance should be
/// smaller than sum of the shape radii.
/// @warning the sweeps must have the same time interval.
/// @return the fraction between [0,1] in which the shapes first touch.
/// fraction=0 means the shapes begin touching/overlapped, and fraction=1 means the shapes don't touch.
public static float CalculateTimeOfImpact(ref TOIInput input, Shape shapeA, Shape shapeB)
{
++b2_toiCalls;
Sweep sweepA = input.sweepA;
Sweep sweepB = input.sweepB;
Debug.Assert(sweepA.t0 == sweepB.t0);
Debug.Assert(1.0f - sweepA.t0 > Settings.b2_FLT_EPSILON);
float radius = shapeA._radius + shapeB._radius;
float tolerance = input.tolerance;
float alpha = 0.0f;
int k_maxIterations = 1000; // TODO_ERIN b2Settings
int iter = 0;
float target = 0.0f;
// Prepare input for distance query.
SimplexCache cache;
DistanceInput distanceInput;
distanceInput.useRadii = false;
for (;;)
{
XForm xfA, xfB;
sweepA.GetTransform(out xfA, alpha);
sweepB.GetTransform(out xfB, alpha);
// Get the distance between shapes.
distanceInput.transformA = xfA;
distanceInput.transformB = xfB;
DistanceOutput distanceOutput;
Distance.ComputeDistance(out distanceOutput, out cache, ref distanceInput, shapeA, shapeB);
if (distanceOutput.distance <= 0.0f)
{
alpha = 1.0f;
break;
}
SeparationFunction fcn = new SeparationFunction(ref cache, shapeA, ref xfA, shapeB, ref xfB);
float separation = fcn.Evaluate(ref xfA, ref xfB);
if (separation <= 0.0f)
{
alpha = 1.0f;
break;
}
if (iter == 0)
{
// Compute a reasonable target distance to give some breathing room
// for conservative advancement. We take advantage of the shape radii
// to create additional clearance.
if (separation > radius)
{
target = Math.Max(radius - tolerance, 0.75f * radius);
}
else
{
target = Math.Max(separation - tolerance, 0.02f * radius);
}
}
if (separation - target < 0.5f * tolerance)
{
if (iter == 0)
{
alpha = 1.0f;
break;
}
break;
}
#if false
// Dump the curve seen by the root finder
{
int N = 100;
float dx = 1.0f / N;
float xs[N + 1];
internal abstract float ComputeTOI(ref Sweep sweepA, ref Sweep sweepB);
