Gantt OnDemand utilise JIRA’s built-in features, such as links, time estimates and sub-tasks to render gantt charts. The concept is simple, to illustrate dependency between two issues (order in which tasks should be completed) you need to create a standard "block" or "blocked by" link between them. Width of an issue on the chart and color depends on provided time estimates and logged work.
Click on the list item below to read more about main chart rendering concepts: