// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Incoprea
// Check parallelism of two sampled edges
// Not compiled or tested in-world
// Setup: Put in the root of a spare owned object/linkset. Child touch handlers may consume events. Touch endpoints of edgeA, then endpoints of edgeB. Collect 4 owner touches; the next touch starts another measurement.
// Stop / restore: Reset clears collected points; disable/remove to stop. No geometry is changed.
// Notes: The angle is direction-independent; reversing an edge does not turn parallel into180 degrees. Results use actual touch positions in region coordinates, not hidden mesh dimensions.
// License: see LICENSE in this distribution.
// Original Incoprea. MIT. Live touch measurements only.
list points;
default
{
    touch_start(integer detectedCount)
    {
        if(llDetectedKey(0)!=llGetOwner())return;
        if(llDetectedTouchFace(0)<0)
        {
            llOwnerSay("Touch position unavailable.");
            return;
        }
        if(llGetListLength(points)>=4)points=[];
        points+=[llDetectedTouchPos(0)];
        integer collected=llGetListLength(points);
        if(collected<4)
        {
            llOwnerSay("Recorded point "+(string)collected+" of 4.");
            return;
        }
        vector a=llList2Vector(points,0);
        vector b=llList2Vector(points,1);
        vector c=llList2Vector(points,2);
        vector d=llList2Vector(points,3);
        vector u=b-a;
        vector v=d-c;
        if(llVecMag(u)<0.000001||llVecMag(v)<0.000001)
        {
            llOwnerSay("Zero-length edge.");
            return;
        }
        float dot=llFabs(llVecNorm(u)*llVecNorm(v));
        if(dot>1.0)dot=1.0;
        float angle=llAcos(dot)*RAD_TO_DEG;
        float offset=llVecMag((c-a)%u)/llVecMag(u);
        llOwnerSay("Parallelism angle="+(string)angle+" first-start offset="+(string)offset);
    }
    changed(integer flags)
    {
        if(flags&CHANGED_OWNER)llResetScript();
    }
}