Hi,
how would I go ahead to align a row-of-connected-boxes to a spline that the left and right extent of each box stays on the spline as long as possible ? So when I modify the spline that teh boxes are updated interactively. The rotation axises of the boxes also need to be where the yellow dots are and the rotation is limited to where the orange dots are.
You'll need to find the intersections of a circle with the spline to determine the end point of the rectangle. If there is no such node yet, iterations to determine the length from several U values on the spline should get you where you want to be. In case there are several intersection the one with the lowest U value on the spline is the correct one. Positioning the rectangles themselves should be pretty simple as long as everything is flat, but even a 3d spline shouldn't make it more difficult. The start point for the next rectangle is the end point of the former one as long as the spline is moving in one direction. Otherwise you'll need to switch the end point.
... one problem coming p is that when I animate the curve, then at a certain point the constrained boxes flip over ... is there a solution to avoid the flipping ?
well I think I've mentioned 'rolling'. If entire chain is placed on some imaginary plane, or something close to that, you can enable 2d chain, and set the chain up vector for entire chain - or use something else to adjust up vector. If you want to define rotation by positions in space (like here), you want three positions, two aren't enough.
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