etDuration( 1 ).play();
			mixer.update( rand( 10 ) );
			mixer.timeScale = rand( 0.9, 1.1 );
			birds.push( {
				mixer,
				mesh,
			} );

		}

	} );

	window.s = scene;

	if ( useFog ) {

		const vertexShader = `
    varying vec3 vWorldPosition;
    void main() {
      vec4 worldPosition = modelMatrix * vec4( position, 1.0 );
      vWorldPosition = worldPosition.xyz;
      gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
    }
    `;

		const fragmentShader = `
    uniform vec3 t