FitTextToBoundary.py

import rhinoscriptsyntax as rs
import scriptcontext as sc
import Rhino


def FitTextToBoundary():
    """
    Get the BBs and center the text in the curve 
    
    Get the text BB. 
    Line from BB center through each corner - extend by curve BB diagaonal
    intersections of these corner lines to the curve
    set text height to suit 
    Move to center again
    replace object
    """
    
    tol = sc.doc.ModelAbsoluteTolerance
    while True:
        idCrv = rs.GetObject('Select the bounding curve', filter = 4, preselect=True)
        if not idCrv: return
        crv = rs.coercecurve(idCrv)
        rc, crvPlane = crv.TryGetPlane()
        
        crvBB = crv.GetBoundingBox(True)
        crvCen = crvBB.Center
        distance = (crvBB.Diagonal.Length)/2
        
        idText = rs.GetObject('Select the text', filter=rs.filter.annotation)
        if not idText: return
        textObj = rs.coercerhinoobject(idText)
        geo = rs.coercegeometry(idText)
        
        bb = geo.GetBoundingBox(True)
        textCen = crvPlane.ClosestPoint(bb.Center)
        geo.Translate(crvCen-textCen)
    
        bb = geo.GetBoundingBox(True)
        textCen = crvPlane.ClosestPoint(bb.Center)
        pts = bb.GetCorners()
        pts = [crvPlane.ClosestPoint(pt) for pt in pts]
        
        ints = []
        for n in range(0, 4):
            vecDir = textCen-pts[n]
            vecDir *= distance
            lineCrv = Rhino.Geometry.LineCurve(textCen, pts[n]+vecDir )
            info = Rhino.Geometry.Intersect.Intersection.CurveCurve(crv, lineCrv, tol, tol)
            if len(info) ==0: continue
            pt = info[0].PointA
            ints.append(pt)
    
        vec = ints[3]-ints[0]
        h = vec.Length
        h *= .9
        geo.TextHeight = h
        textCen = crvPlane.ClosestPoint(geo.GetBoundingBox(True).Center)
        geo.Translate(crvCen-textCen)
    
        sc.doc.Objects.Replace(idText, geo)
    
        sc.doc.Views.Redraw()

if __name__ == '__main__':FitTextToBoundary()

Note this does not work with multi line text.