enables the smart rendering mode for gantt's tasks and links rendering
gantt.config.smart_rendering = true;
Starting from v6.2, the smart rendering is enabled by default, as it is included in the core dhtmlxgantt.js file. Thus, you don't need to include the dhtmlxgantt_smart_rendering.js file on the page to make smart rendering work.
If you connect the dhtmlxgantt_smart_rendering.js file, which is from the old version, it will override the improvements of the new built-in smart_rendering extension.