[Closed] Find intersection point between a vector (2 points) and closed spline

2 points sounds more like segment not vector.
Collect points of your spline using interpCurve3D and then check segmentSegment intersection between your segment and segment defined by spline point n and point n+1

something like this

delete objects

Thetex = text text:"D" size:115
centerpivot thetex
thetex.pos = [0,0,0]
pt1 = point size:.5 cross:on box:off axistripod:off wirecolor:(color 88 144 225)
pthCon = pt1.pos.controller = Path_Constraint Follow:on path:$Text001
deleteKeys pt1.pos.controller #allKeys
pt1.pos.controller.percent = 45.4
pt2 = point pos:[7.3,37.1,0] size:.5 cross:off box:on axistripod:off wirecolor:(color 88 144 225)
NeedPoiont = point pos:[-26.65,36.5,0] size:.5 cross:on box:off axistripod:off wirecolor:Red
pthCon = needPoiont.pos.controller = Path_Constraint Follow:on path:$Text001
deleteKeys needPoiont.pos.controller #allKeys
needPoiont.pos.controller.percent = 46.0



convertToSplineShape Thetex
theTexPts = #()
for i=1 to numsplines Thetex do (
    
    pts = for p=0.0 to 1.0 by 0.01 collect interpCurve3D Thetex i p
    
    append theTexPts pts    
    
)

for splinePts in theTexPts do (
    
    for p in splinePts do point pos:p centermarker:on cross:off wirecolor:yellow
    
)





fn segSegIntersection a1 a2 b1 b2 = (
    
    -- calc whether segment a1a2 intersects segment b1b2
    
)


a1 = Thetex.center
a2 = pt2.center

pointsOfIntesection = #()

for s=1 to theTexPts.count do (
    
    splinePts = theTexPts[s]
    count = splinePts.count
    
    for i=1 to count do (
        
        j = if i == count then 1 else i + 1
            
        result = segSegIntersection a1 a2 splinePts[i] splinePts[j]
        
        if result != undefined do (
            
            append pointsOfIntesection #( s /* spline index */, result /* point of intersection */ )
            
        )
        
    )
    
)

i use this function to find the intersection between to splines or vectors from the sticky page Geometrical calculations : points, lines, planes : intersections,

fn lineLineIntersect pA pB pC pD = 
    (
    local a=pB-pA
    local b=pD-pC
    local c=pC-pA
    local cross1 = cross a b
    local cross2 = cross c b
    pA + ( a*( (dot cross2 cross1)/((length cross1)^2) ) )
    )

if i use this fn instead of fn segSegIntersection a1 a2 b1 b2 still doesnt get the intersection

How are you suppose to have a valid intersection point using lineLine Intersection? lineLine Intersection will return the intersection point that is outside of spline shape most of the time.
google for segmentSegment intersection. There’re plenty of examples on stackoverflow and github available

or…

(
delete objects
txt = text text:"G"
txt.center = [0,0,0]

p1 = [-50,-50,0]
p2 = [ 25, 50,0]

point pos:p1 centermarker:on cross:off wirecolor:yellow
point pos:p2 centermarker:on cross:off wirecolor:yellow
    
redrawViews()

gc()
t1=timestamp()
hf = heapfree

    
with redraw off (
    
    with undo off (
        
        addModifier txt (Extrude amount:666)

        vec = normalize (p1 - p2)
        _ray = ray vec (p1 + [0,0,txt.center.z])
                
        rmgi = RayMeshGridIntersect()
        rmgi.initialize 20
        rmgi.addNode txt
        rmgi.buildGrid()

--         rmgi.intersectray _ray.pos _ray.dir true
        hits = rmgi.intersectSegment p1 p2 true

        if hits > 0 do (
            
            for i=1 to hits do (
                
                point pos:(p1 - (rmgi.getHitDist i) * vec) centermarker:on cross:off wirecolor:orange
                
            )
            
            
        )

        rmgi.free()
        
                
        deleteModifier txt 1
        
    )
    
)


format "Time: %sec. Mem: %
" ((timestamp()-t1)/1000 as float) (hf-heapfree)

)