FlexGanttFX Gantt Chart Library Goes Open Source Under AGPL License

Dirk Lemmerman has made FlexGanttFX publicly available as open source code after keeping the resource-scheduling library proprietary for over a decade and a half. The shift reflects a growing trend among software vendors to release commercial projects under copyleft licenses that impose stricter terms than permissive alternatives.

What is FlexGanttFX?#

FlexGanttFX is a framework built on JavaFX that enables developers to create and display Gantt charts—visual timelines showing task progress and interdependencies. These diagrams are staples in industries spanning logistics, aviation, healthcare, and software development, helping teams coordinate parallel and sequential work by illustrating how tasks relate and affect one another.

The library's architecture rests on four core building blocks: rows organized as a resource tree, activities representing time-constrained work items, layers that manage visual ordering and visibility, and links that capture task dependencies. Time handling leverages Java's java.time.Instant, supporting rendering granularity from milliseconds to decades while accounting for time zones, daylight-saving shifts, weekends, and business hours as part of the data model rather than visual styling.

Performance Through Canvas Rendering#

FlexGanttFX achieves smooth performance with complex charts by blending Canvas-based rendering alongside standard JavaFX nodes. Rather than creating hundreds or thousands of individual visual objects, the library renders the entire chart to a single Canvas, dramatically improving responsiveness. This hybrid approach allows flexible layout options: a standard layout displays classic bars, a chart layout renders lines or areas suitable for overlay with capacity curves, and a pool layout stacks overlapping activities into horizontal bands.

The JavaFX foundation also allows deployment across desktop and mobile platforms, with runnable demonstrations available on GitHub showcasing rendering and editing capabilities.

The AGPL Strategic Choice#

Lemmerman selected the GNU Affero General Public License (AGPL) for the release—a decision shared by other commercial-yet-open projects. Unlike permissive licenses such as Apache 2.0, AGPL includes a clause requiring companies that modify and deploy modified versions over a network to publish their source code publicly, even if they don't distribute the software itself. This copyleft approach creates licensing friction: many SaaS and cloud vendors sidestep AGPL projects altogether to avoid disclosure obligations.