// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Incoprea
// Project child onto an authored rail
// Not compiled or tested in-world
// Setup: Set A and B. Put in nonphysical child; owner-touch previews/restores.
// Stop / restore: Owner-touch again to restore the startup snapshot before removal or reset, unless setup describes a different cycle. Do not relink during a preview.
// Notes: Use a spare modifiable build. Saved state lives only in script memory. Centerline alignment, not a moving constraint. Degenerate endpoints rejected.
// License: see LICENSE in this distribution.
// Original Incoprea. MIT. Not compiled or tested in-world.
integer preview;
vector A=<-1.0,0.0,0.0>;
vector B=<1.0,0.0,0.0>;
vector home;
default
{
    state_entry()
    {
        home=llGetLocalPos();
    }
    touch_start(integer n)
    {
        if(llDetectedKey(0)!=llGetOwner())return;
        if(llGetLinkNumber()<2||llGetStatus(STATUS_PHYSICS)||llVecDist(A,B)<0.001)return;
        preview=!preview;
        if(preview)
        {
            vector d=B-A;
            float t=((home-A)*d)/(d*d);
            if(t<0.0)t=0.0;
            if(t>1.0)t=1.0;
            llSetLinkPrimitiveParamsFast(LINK_THIS,[PRIM_POS_LOCAL,A+d*t]);
        }
        else
        {
            llSetLinkPrimitiveParamsFast(LINK_THIS,[PRIM_POS_LOCAL,home]);
        }
    }
}