function filter(p) {    
    /* Random near-zero value used as "zero" to prevent two sequential updates from being
    exactly the same (which would cause them to be ignored) */
    var nearZero = 0.0001 * Math.random() + 0.001;
    
    /* Filter in which you define a zone that no entites can enter */
    /* Default box coordinates correspond to stage area in dev-demo */
    if (p.position) {
        /* Define the points that create the "NO ENTITIES ALLOWED" box */
        var BigStageMin = {x: 90, y: -1, z: 23};
        var BigStageMax = {x: 109, y: 10, z: 30};
        var ProceniumMin = {x: 97.5, y: -1, z: 30};
        var ProceniumMax = {x: 102, y: 5, z: 33.5};
        /* Define the point that you want entites that enter the box to appear */
        var resetPoint = {x: Math.random() * (103.6 - 95.4) + 95.4, y: 2.5 + 0.00001 * Math.random(), z: 38.1557};
        var x = p.position.x;
        var y = p.position.y;
        var z = p.position.z;
        if (((x > BigStageMin.x && x < BigStageMax.x) &&
            (y > BigStageMin.y && y < BigStageMax.y) &&
            (z > BigStageMin.z && z < BigStageMax.z)) ||
            ((x > ProceniumMin.x && x < ProceniumMax.x) &&
            (y > ProceniumMin.y && y < ProceniumMax.y) &&
            (z > ProceniumMin.z && z < ProceniumMax.z))) {
            p.position = resetPoint;
            if (p.velocity) {
                p.velocity = {x: 0, y: nearZero, z: 0};
            }
            if (p.acceleration) {
                p.acceleration = {x: 0, y: nearZero, z: 0};
            }
        }
    }
    
    /* Only apply the filters below if the entity is inside the theater */
    var WholeTheaterMin = {x: 79.0, y: -2.9, z: 14.0};
    var WholeTheaterMax = {x: 119, y: 13.0, z: 56};
    if ((x > WholeTheaterMin.x && x < WholeTheaterMax.x) &&
    (y > WholeTheaterMin.y && y < WholeTheaterMax.y) &&
    (z > WholeTheaterMin.z && z < WholeTheaterMax.z)) {
        /* Clamp velocity to maxVelocity units/second. Zeroing each component of acceleration keeps us from slamming.*/
        if (p.velocity) {
            var maxVelocity = 5;
            function sign(val) {
                if (val > 0) {
                    return 1;
                } else if (val < 0) {
                    return -1;
                } else {
                    return 0;
                }
            }
            if (Math.abs(p.velocity.x) > maxVelocity) {
                p.velocity.x = sign(p.velocity.x) * (maxVelocity + nearZero);
                p.acceleration.x = nearZero;
            }
            if (Math.abs(p.velocity.y) > maxVelocity) {
                p.velocity.y = sign(p.velocity.y) * (maxVelocity + nearZero);
                p.acceleration.y = nearZero;
            }
            if (Math.abs(p.velocity.z) > maxVelocity) {
                p.velocity.z = sign(p.velocity.z) * (maxVelocity + nearZero);
                p.acceleration.z = nearZero;
            }
        }
        
        
        /* Reject if modifications made to Model properties, OR */
        /* Reject if modifications made to source URL (for Web entities) OR */
        /* Reject if modifications made to dimensions */
        if (p.modelURL !== undefined || p.compoundShapeURL || p.shape || p.shapeType || p.url ||
        p.fps || p.currentFrame || p.running || p.loop || p.firstFrame || p.lastFrame || p.hold ||
        p.textures !== undefined || p.xTextureURL !== undefined || p.yTextureURL !== undefined ||
        p.zTextureURL !== undefined ||  p.sourceUrl !== undefined || p.dimensions) {
            return false;
        }
    }

    return p;
}