private void InitializeHelpers()
{
this.computedInputPose = new ComputedValue <SlingShotPose>(() => this.ComputeInputPose());
this.computedTangentPositionR = new ComputedValue <SCNVector3>(() => this.TangentPosition(this.FixturePositionR));
this.computedTangentPositionL = new ComputedValue <SCNVector3>(() => this.TangentPosition(this.FixturePositionL));
this.computedBetaAngle = new ComputedValue <float>(() =>
{
var d = SCNVector3.Normalize(this.ballPosition - this.CenterPosition);
var t = SCNVector3.Normalize(this.TangentPositionL - this.ballPosition);
var quaternion = SimdExtensions.CreateQuaternion(d, t);
quaternion.ToAxisAngle(out SCNVector3 _, out float angle);
return(2f * angle);
});
this.computedCenterPosition = new ComputedValue <SCNVector3>(() =>
{
var direction = SCNVector3.Cross(this.UpVector, this.TangentPositionR - this.TangentPositionL);
return(this.ballPosition - SCNVector3.Normalize(direction) * 1.25f * this.ballRadius);
});
this.computedRestPose = new ComputedValue <SlingShotPose>(() =>
{
var data = new SlingShotPose();
for (var i = 0; i < this.restPoseTransforms.Count; i++)
{
var transform = this.restPoseSpace * this.restPoseTransforms[i];
var p = new SCNVector3(transform.Column3.X, transform.Column3.Y, transform.Column3.Z);
var t = SimdExtensions.CreateQuaternion(transform).Act(new SCNVector3(1f, 0f, 0f));
var l = 0f;
if (i > 0)
{
l = data.Lengths[i - 1] + (p - data.Positions[i - 1]).Length;
}
data.Positions.Add(p);
data.Tangents.Add(t);
data.Lengths.Add(l);
}
return(data);
});
}
public SlingShotPose ComputeInputPose()
{
// note the -1 here differs from other usage
var data = new SlingShotPose {
UpVector = -this.UpVector /* negated because the strap Y-axis points down */
};
var startBend = this.CurrentLengthL / this.CurrentTotalLength;
var endBend = 1f - this.CurrentLengthR / this.CurrentTotalLength;
var leatherOnStraights = this.OriginalLeatherLength - this.CurrentLengthOnBall;
var segmentAStart = 0f;
var segmentAEnd = this.CurrentLengthL - leatherOnStraights * 0.5f;
var segmentCStart = segmentAEnd + this.OriginalLeatherLength;
var segmentCEnd = this.CurrentTotalLength;
var originalLeatherRange = this.OriginalLeatherLength / this.OriginalTotalLength;
var currentLeatherRange = this.OriginalLeatherLength / this.CurrentTotalLength;
for (var i = 0; i < this.SimulatedTransformCount; i++)
{
var l = this.OriginalTotalLength * (float)i / (float)(this.SimulatedTransformCount - 1f);
var u = l / this.OriginalTotalLength;
// remap the u value depending on the material (rubber vs leather)
var isRubber = Math.Abs(0.5f - u) > originalLeatherRange * 0.5f;
if (isRubber)
{
if (u < 0.5f)
{
u = u / (0.5f - originalLeatherRange * 0.5f);
u = (segmentAStart + (segmentAEnd - segmentAStart) * u) / this.CurrentTotalLength;
}
else
{
u = 1f - (1f - u) / (0.5f - originalLeatherRange * 0.5f);
u = (segmentCStart + (segmentCEnd - segmentCStart) * u) / this.CurrentTotalLength;
}
}
else
{
u = (startBend + endBend) * 0.5f - (0.5f - u) * (currentLeatherRange / originalLeatherRange);
}
var p = SCNVector3.Zero;
var t = SCNVector3.UnitX;
if (u < startBend)
{
// left straight
var value = u / startBend;
p = SimdExtensions.Mix(this.FixturePositionL,
this.TangentPositionL,
new SCNVector3(value, value, value)); // left rubber band
t = SCNVector3.Normalize(this.TangentPositionL - this.FixturePositionL);
}
else if (u > endBend)
{
// right straight
var value = (1f - u) / (1f - endBend);
p = SimdExtensions.Mix(this.FixturePositionR,
this.TangentPositionR,
new SCNVector3(value, value, value)); // right rubber band
t = SCNVector3.Normalize(this.FixturePositionR - this.TangentPositionR);
}
else
{
// on the ball
var upv = this.UpVector;
var rot = SCNQuaternion.FromAxisAngle(upv, -this.BetaAngle * (u - startBend) / (endBend - startBend));
p = this.ballPosition + rot.Act(this.TangentPositionL - this.ballPosition);
t = SCNVector3.Cross(upv, SCNVector3.Normalize(this.ballPosition - p));
}
data.Positions.Add(p);
data.Tangents.Add(t);
data.Lengths.Add(l);
}
return(data);
}