Rob Fearnside on making Lightworks' code OS independent

Lightworks for Linux: The developer's story

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Lightworks, a high-end non-linear video editor, was approaching its public testing phase for its Linux release. Lead Developer Rob Fearnside answered questions from Red Shark News about how it got to this stage.

Editor's note: The intent for Lightworks to go open source seems to have been abandoned. It remains a no-cost option for cross-platform video editing, but for open source video editing options, read our state of video editing report.

When did you decide to make the majority of Lightworks' code OS independent and what was your approach to doing this?

The Lightworks codebase is quite large—close to a million lines of code altogether—and some of it has been in existence for nearly twenty years. When we started the move to make it cross-platform 18 months ago, we were faced with a number of challenges, including:

  • How do you rewrite that much code in a sensible timeframe
  • How do you keep shipping Windows builds whilst the work is underway?

Our solution was to avoid rewriting the Windows-specific code at all (it was, after all, tried, tested and optimized). Instead, we decided to move it to a new operating system dependent layer which we engineered to have an OS independent interface. Once this was complete, we were then able to begin work on a Linux implementation of that same layer. In essence, the Lightworks code is now split in two—the OS independent code (eg. editing, play-engine, etc) which uses the OS dependent code (eg. file access, threading, etc).

What percentage of the code is now OS independent?

The OS independent code accounts for about 97% of the total codebase. The bulk of the work in porting to Linux was actually in re-engineering the existing code, not in writing the Linux-specific layer.

What was the hardest thing about porting to Linux?

In order to get the very best performance, Lightworks' Windows layer uses Direct3D for all the video scaling, effects, and colour-space conversion. Linux of course doesn't have Direct3D, so we had to reimplement all the Linux GPU specific code using OpenGL. The multi-threaded nature of the Lightworks software made some of the OpenGL support difficult to write. In particular, updating video/playback images from a non-ui thread was a real challenge, and for a while I wasn't sure it was even possible, but after much head scratching, we found a solution that worked.

How happy are you now with the results?

The initial goal with the Linux version was to try to make it as similar to the Windows version as possible. Now, if you run the two versions side by side, it's extremely difficult to tell them apart, so in that sense, I'm very pleased with the results. Additionally, because we went through the process of splitting the code into OS dependent and independent pieces, we've ended up with a cleaner, more maintainable codebase which will benefit all of our future development across all platforms.

Originally posted on Red Shark News. Reposted with permission.

About the author

Rob Fearnside - Rob is a lead programmer for Lightworks. He joined the company in 1993 where he spent over a decade working on a number of areas including the user-interface and video effects. He then moved to Quantel where he helped create their new effects architecture before eventually returning to Lightworks in 2010.