How to use the babylonjs-procedural-textures.GrassProceduralTexture function in babylonjs-procedural-textures

scene.enablePhysics(gravityVector, new CannonJSPlugin);

    scene.clearColor = BABYLON.Color4.FromColor3(BABYLON.Color3.Black());

    var camera = new BABYLON.FreeCamera("Camera", new BABYLON.Vector3(0, 0, -10), scene);
    //var camera = new BABYLON.UniversalCamera("UniversalCamera", new BABYLON.Vector3(0, 0, -10), scene);
    camera.checkCollisions = true;
    camera.applyGravity = true;
    // Targets the camera to a particular position. In this case the scene origin
    camera.setTarget(BABYLON.Vector3.Zero());

    // Attach the camera to the canvas
    camera.attachControl(canvas, true);

    var grassMaterial = new BABYLON.StandardMaterial("grass", scene);
    var grassTexture = new GrassProceduralTexture("textgrass", 256, scene);
    grassMaterial.ambientTexture = grassTexture;
    grassMaterial.diffuseTexture= grassTexture;

    // Create Ground
    var ground = BABYLON.Mesh.CreatePlane("ground", 25.0, scene);
    ground.position = new BABYLON.Vector3(0, -5, 0);
    ground.rotation = new BABYLON.Vector3(Math.PI / 2, 0, 0);

    ground.material = grassMaterial;
 
    // Create the 3D UI manager
    var manager = new GUI.GUI3DManager(scene);
    // Create a horizontal stack panel
    var panel = new GUI.StackPanel3D();
    panel.margin = 0.02;
    manager.addControl(panel);