[Closed] Shape Check, or finding self intersections of a spline

Basically right now i’m using the bounding box of each segment and doing an intersection test that way, but its not the most elegant. I didn’t know if people had a better solution.

see sdk -> editspl.cpp -> SplineSelfIntersects

that’s not the most elegant either being like most max code brute force stylee

Hehe…true, after looking at, but it will work. Thanks Denis!

didn’t test it in max, but it should work

(
	g = (dotNetClass "Autodesk.Max.GlobalInterface").Instance
	inode = g.coreinterface7.getinodebyhandle $.inode.handle
	shp = ((inode.EvalWorldState (int currenttime) true).obj).shape_
	splines = for i=0 to shp.SplineCount-1 collect shp.GetSpline i
	
	for i=1 to splines.count do
	(
		format "Spline % is self-intersecting: %\n" i (splines[i].SelfIntersects)
		
		for j=i+1 to splines.count where splines[i].IntersectsSpline splines[j] do
		(
			format "Spline % intersects spline %\n" i j
		)
		
	)

)

I was always interested to know not the fact of intersection, but to get all intersection points.

Sure, but I guess it’s better to know which splines are actually intersecting before attempting to find an exact point.
I remember here was a thread where you and @aandres discussed how to calc the intersection points between bezier splines. But forum search is too advanced to find it

the issue is too advanced for this forum’s search

just today i wrote the ‘two splines intersection’ function for my mxs extension. I found that using linear interpolation gives the best result by performance. the accuracy is OK for most cases.

the one in the .cpp, if i’m reading right, just does 2 dimensional collision. For that one i already found a relatively easy one on line, though won’t work for bezier. So i’ll have to read this bezier curves paper. Thanks!

				fn FindSlope=
				(
					A = pt1.Y - pt0.Y
					B = pt0.X - pt1.X
					C = A * pt0.X + B * pt0.Y
				),

				
				-- https://pastebin.com/iQDhQTFN 
				fn Intersect2D otherLine =
				(
					out = #()
					local determinant = A * otherLine.B - otherLine.A * B;

					if  EqualValues(determinant)(0) == false do -- true they are parallel
					(
						--Cramer's Rule
						local x = (otherLine.B * C - B * otherLine.C) / determinant;
						local y = (A * otherLine.C - otherLine.A * C) / determinant;

						append out [x,y];
					)
					/*return*/ out
				),

the 3 dimensional one has been a little trickier. This one works for simple linear 2d lines.