// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Incoprea
// Check a point against a convex boundary
// Not compiled or tested in-world
// Setup: Use a spare owned prim. Set ordered convex polygon VERTICES and test POINT. Touch for owner-only calculation output.
// Stop / restore: Remove/disable. Does not sense, collide with, or modify actual objects.
// Notes: Requires a convex polygon with consistent winding; zero cross products count as boundary and therefore inside.
// License: see LICENSE in this distribution.
// Original Incoprea. MIT. Ideal geometry only.
list VERTICES=[<0.0,0.0,0.0>,<4.0,0.0,0.0>,<5.0,3.0,0.0>,<1.0,5.0,0.0>];
vector POINT=<2.0,2.0,0.0>;
default
{
    touch_start(integer detectedCount)
    {
        if(llDetectedKey(0)!=llGetOwner())return;
        integer n=llGetListLength(VERTICES);
        if(n<3)
        {
            llOwnerSay("Need three vertices.");
            return;
        }
        integer positive;
        integer negative;
        integer i;
        for(i=0;i<n;++i)
        {
            vector a=llList2Vector(VERTICES,i);
            vector b=llList2Vector(VERTICES,(i+1)%n);
            float cross=(b.x-a.x)*(POINT.y-a.y)-(b.y-a.y)*(POINT.x-a.x);
            if(cross>0.000001)positive=TRUE;
            if(cross< -0.000001)negative=TRUE;
        }
        llOwnerSay("Inside/boundary="+(string)(!(positive&&negative)));
    }
}