function filter(p, isAdd) {    
    
    
    /* 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: 31};
        var ProceniumMin = {x: 97.5, y: -1, z: 31};
        var ProceniumMax = {x: 102, y: 10, z: 33.5};
        /* Exclude the two mats underneath the whiteboards on stage, used
        for the demo on Friday, 2017-02-03 */
        var WhiteboardMat1Min = {x: 94.03635, y: -0.9196, z: 27.78185};
        var WhiteboardMat1Max = {x: 98.08725, y: 4, z: 30.59055};
        var WhiteboardMat2Min = {x: 100.83045, y: -0.9196, z: 27.78185};
        var WhiteboardMat2Max = {x: 104.88135, y: 4, z: 30.59055};
        
        var x = p.position.x;
        var y = p.position.y;
        var z = p.position.z;
        
        var isOnStage = (((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)));
        var isOnWhiteboardMat1 = ((x > WhiteboardMat1Min.x && x < WhiteboardMat1Max.x) && 
            (y > WhiteboardMat1Min.y && y < WhiteboardMat1Max.y) &&
            (z > WhiteboardMat1Min.z && z < WhiteboardMat1Max.z));
        var isOnWhiteboardMat2 = ((x > WhiteboardMat2Min.x && x < WhiteboardMat2Max.x) && 
            (y > WhiteboardMat2Min.y && y < WhiteboardMat2Max.y) &&
            (z > WhiteboardMat2Min.z && z < WhiteboardMat2Max.z));
        
        if (isOnStage && !(isOnWhiteboardMat1 || isOnWhiteboardMat2)) {
            /* this basically makes the offending entity go away.  Feels like
             * overkill, but a place to start given changes we've seen recently
             */
            p.collisionless = 1;
            p.lifetime = 1.0;
        }
    }
    
    /* Only apply the filters below if the entity is inside the theater */
    /* AND if this entity wasn't just spawned */
    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) &&
    !isAdd) {
        /* together the density, dimensions and velocity filters cap momentum, which 
         * helps with how griefed you are by someone whacking you with things
         */
        
        var MAX_DENSITY = 1500;
        var MAX_EXTENT = 0.6;
        var MAX_VELOCITY = 4.0;
        /* cap density at standard 1 kg/m^3) */
        if (p.density && p.density > MAX_DENSITY) {
             p.density = MAX_DENSITY;
        }

        /* cap bounding box */
        if (p.dimensions) {
            function capDimension(d) {
                if (d > MAX_EXTENT) {
                    return MAX_EXTENT;
                }
                return d;
            }

            p.dimensions.x = capDimension(p.dimensions.x);
            p.dimensions.y = capDimension(p.dimensions.y);
            p.dimensions.z = capDimension(p.dimensions.z);
        }

        /* Clamp magnitude of the velocity vector 
         * for now, not changing acceleration 
         */
        if (p.velocity) {
            function magnitude(v) {
                return Math.sqrt((v.x * v.x) + (v.y * v.y) + (v.z * v.z));
            }
            var magV = magnitude(p.velocity);
            if (magV > MAX_VELOCITY) {
                var ratio = MAX_VELOCITY/magV;
                // reduce it proportionally
                p.velocity.x = p.velocity.x * ratio;
                p.velocity.y = p.velocity.y * ratio;
                p.velocity.z = p.velocity.z * ratio;
            }
        }
        
        /* 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;
}