解答：修改 SquareGeometry() 中的 uvs.push：

var uvs = [];
uvs.push( new THREE.Vector2( 0.75, 0.25 ) );
uvs.push( new THREE.Vector2( 1.0, 0.25 ) );
uvs.push( new THREE.Vector2( 1.0, 0.5 ) );
uvs.push( new THREE.Vector2( 0.75, 0.5 ) );