// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Incoprea
// Check a two-link display arm reach
// Not compiled or tested in-world
// Setup: Put in a spare owned prim. Set lengths L1/L2 and target X/Y. Owner touch prints calculations only.
// Stop / restore: Disable/remove. No prim motion or appearance is changed.
// Notes: Returns one elbow configuration. Singular and unreachable targets are reported; this does not control a rig or avatar.
// License: see LICENSE in this distribution.
// Original Incoprea. MIT. Motion planning only.
float L1=3.0;
float L2=2.0;
float X=3.0;
float Y=2.0;
default
{
    touch_start(integer detectedCount)
    {
        if(llDetectedKey(0)!=llGetOwner())return;
        if(L1<=0.0||L2<=0.0)
        {
            llOwnerSay("Positive lengths required.");
            return;
        }
        float d2=X*X+Y*Y;
        float c=(d2-L1*L1-L2*L2)/(2.0*L1*L2);
        if(c< -1.0||c>1.0||d2<0.000001)
        {
            llOwnerSay("Unreachable or singular target.");
            return;
        }
        float elbow=llAcos(c);
        float shoulder=llAtan2(Y,X)-llAtan2(L2*llSin(elbow),L1+L2*llCos(elbow));
        llOwnerSay("Shoulder degrees="+(string)(shoulder*RAD_TO_DEG)+" elbow degrees="+(string)(elbow*RAD_TO_DEG));
    }
}