It looks like speed changes between control point path segment. See gif below.
I set the speed of each node to be the same. But it changes between control points.
On short segment node move slower.
Possible SplinePath Speed Bug
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What you mean?
If I have a linear line to travel. With a constant speed ( same for each characters), Shouldn’t I get a constant gap between the characters.
I’m not sure if the interpolate position GetPoint return the correct position. The following calculation is done similar to a single node Move method.
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I do think this is intended behaviour for a spline path.
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This is the calculation.
float newDistance = lstPed_[i]->relativePosInQueue_ + dt * lstPed_[i]->speed_;
float traveled_ = newDistance / queuePath_->GetLength();
lstPed_[i]->GetNode()->SetWorldPosition(queuePath_->GetPoint(traveled_));
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If you divide the speed by the length of the current segment it should be constant.
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I don’t believe this is correct.
If it is a linear. It is easy to get the correct position.
The behaviour is wrong. Theoretically.
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For your use case, yes.
The interpolation logic is consistent along different interpolation modes.
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The current logic return incorrect position as you can see in the gif.
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What if you were to move the knots during runtime? Which behaviour would you expect?
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I recalculate the length using the built in SplinePath function when I move the knots.
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Anyway maybe leave it here.
I’m only trying to report a possible bug/behaviour.
I will fix the interpolation.
The math should be easy.
Best regards
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“There are a few ways to move along at a constant speed along a path whose “segments” are not a constant length - and it’s not trivial to make them that way.” - ClickerMonkey
This supports my not-a-bug theory.
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Thanks I have done this a number of years ago in Irrlicht.
Best regards
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Are you talking about linear interpolation between control points or more complex cases too?
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Yes! Navigate through multi control points.
For linear polyline.
It is easier to fix the behaviour. E.g.
I speed up my simulation clock to reduce the file size of the gif.
For catmul-rom I can use this multi linear line segment method or the calculus method via simson’s rule.
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A simple piecewise linear over existing interpolation.
I first linearized the spline.
void LinearisedPath()
{
if (queuePath_->GetControlPoints().Size() > 2)
{
Spline spline = queuePath_->GetSpline();
int size = queuePath_->GetControlPoints().Size();
double rate = 0.001f;
splinePath_.Clear();
for (float f = 0.f; f <= 1.0f; f += rate)
{
Vector3 b = spline.GetPoint(f).GetVector3();
splinePath_.AddKnot(b);
}
}
else if (queuePath_->GetControlPoints().Size() == 2)
{
splinePath_ = queuePath_->GetSpline();
}
}
Then loop through like below.
Vector<Variant> knots_ = splinePath_.GetKnots();
int size = knots_.Size();
int segment = 1;
float sumLength = 0.0f;
for (; segment < size; segment++)
{
float segmentLength = (knots_[segment].GetVector3() - knots_[segment - 1].GetVector3()).Length();
sumLength += segmentLength;
if (sumLength >= relativeDistance)
break;
}
if (segment == size)
{
segment--;
}
Vector3 dir = knots_[segment].GetVector3() - knots_[segment - 1].GetVector3();
dir.y_ = 0;
dir.Normalize();
Vector3 pos = knots_[segment].GetVector3() - dir * (sumLength - character->relativePosInQueue_);
Quaternion Q;
Q.FromLookRotation(dir);
Q.Normalize();
character->GetNode()->SetRotation(Quaternion());
character->GetNode()->SetWorldRotation(Q);
character->GetNode()->SetWorldPosition(pos);
I recommend we have dynamic number of interpolate segment increases with number of control points. This will remove the debug line drawn bug.