/**
     * Unprojects canvas position to a World-space ray.
     */
    var canvasPosToWorldRay = (function () {

        var pvMat = mat4.create();
        var pvMatInverse = mat4.create();
        var screenA = vec4.create();
        var screenB = vec4.create();
        var projA = vec4.create();
        var projB = vec4.create();

        return function (canvasPos, worldRayOrigin, worldRayDir) {

            var canvas = Human.renderer.canvas.canvas[0];
            var viewMat = Human.renderer.getViewMat();
            var projMat = Human.renderer.getProjMat();

            mat4.multiply(pvMat, projMat, viewMat); // Projection-view mat
            mat4.invert(pvMatInverse, pvMat); // Inverse projection-view mat

            var canvasWidth = canvas.width;
            var canvasHeight = canvas.height;

            var clipX = (canvasPos[0] - canvasWidth / 2) / (canvasWidth / 2);  // Calculate clip space coordinates
            var clipY = -(canvasPos[1] - canvasHeight / 2) / (canvasHeight / 2);

            screenA[0] = clipX;
            screenA[1] = clipY;
            screenA[2] = -1;
            screenA[3] = 1;

            vec4.transformMat4(projA, screenA, pvMatInverse);
            vec4.scale(projA, projA, 1 / projA[3]);

            screenB[0] = clipX;
            screenB[1] = clipY;
            screenB[2] = 1;
            screenB[3] = 1;

            vec4.transformMat4(projB, screenB, pvMatInverse);
            vec4.scale(projB, projB, 1 / projB[3]);

            vec3.subtract(worldRayDir, projB, projA);
            vec3.normalize(worldRayDir, worldRayDir);

            worldRayOrigin[0] = projB[0];
            worldRayOrigin[1] = projB[1];
            worldRayOrigin[2] = projB[2];
        };
    })();

    /**
     * Returns array of scene objects whose boundaries intersect the given World-space ray.
     */
    var findIntersectingObjects = (function () {

        /**
         * Tests ray for intersection with AABB.
         */
        function rayAABBIntersect(origin, dir, aabb) {

            var lo = -Infinity;
            var hi = +Infinity;
            var dimLo;
            var dimHi;
            var tmp;

            dimLo = (aabb.xmin - origin[0]) / dir[0];
            dimHi = (aabb.xmax - origin[0]) / dir[0];

            if (dimLo > dimHi) {
                tmp = dimLo;
                dimLo = dimHi;
                dimHi = tmp;
            }

            if (dimHi < lo || dimLo > hi) {
                return false
            }

            if (dimLo > lo) {
                lo = dimLo;
            }

            if (dimHi < hi) {
                hi = dimHi;
            }

            dimLo = (aabb.ymin - origin[1]) / dir[1];
            dimHi = (aabb.ymax - origin[1]) / dir[1];

            if (dimLo > dimHi) {
                tmp = dimLo;
                dimLo = dimHi;
                dimHi = tmp;
            }

            if (dimHi < lo || dimLo > hi) {
                return false
            }

            if (dimLo > lo) {
                lo = dimLo;
            }
            if (dimHi < hi) {
                hi = dimHi;
            }

            dimLo = (aabb.zmin - origin[2]) / dir[2];
            dimHi = (aabb.zmax - origin[2]) / dir[2];

            if (dimLo > dimHi) {
                tmp = dimLo;
                dimLo = dimHi;
                dimHi = tmp;
            }

            if (dimHi < lo || dimLo > hi) {
                return false
            }

            if (dimLo > lo) {
                lo = dimLo;
            }

            if (dimHi < hi) {
                hi = dimHi;
            }

            return (lo <= hi);
        }

        return function (origin, dir) {

            var objects = Human.scene.objects;
            var object;
            var boundary;
            var pickId;
            var objectIds;

            for (var objectId in objects) {
                if (objects.hasOwnProperty(objectId)) {

                    object = objects[objectId];

                    boundary = object.getBoundary();

                    if (rayAABBIntersect(origin, dir, boundary)) {

                        pickId = object.pickId;

                        if (pickId !== null && pickId !== undefined) {

                            if (!objectIds) {
                                objectIds = [];
                            }

                            objectIds.push(pickId);

                            //object.setHighlight(true);
                        }
                    } else {
                        //  object.setHighlight(false);
                    }
                }
            }

            return objectIds;
        };
    })();