TurboVNC | About / A Brief Introduction to TurboVNC

TurboVNC is a derivative of VNC (Virtual Network Computing) that is tuned to provide peak performance for 3D and video workloads. TurboVNC was originally a fork of TightVNC 1.3.x. However, the current version of TurboVNC contains a modern X server code base (based on X.org) and a variety of other notable features and fixes relative to TightVNC 1.3.x, including a high-performance cross-platform VNC viewer with session management capabilities, as well as some unique features designed specifically for visualization applications. Some of those features are not available in any other open source Linux/Un*x remote display solutions. TurboVNC compresses 3D and video workloads significantly better than the "tightest" compression mode in TightVNC 1.3.x while using only typically 15-20% of the CPU time of the latter. Using non-default settings, TurboVNC can also match the best compression ratios produced by TightVNC 1.3.x for 2D workloads.

All VNC implementations, including TurboVNC, use the RFB (remote framebuffer) protocol to send “framebuffer updates” from the VNC server to any connected "viewers." Each framebuffer update can contain multiple "rectangles" (regions that have changed since the last update.) As with TightVNC, TurboVNC analyzes each rectangle, splits it into multiple "subrectangles", and attempts to encode each subrectangle using the "subencoding type" that will provide the most efficient compression, given the number of unique colors in the subrectangle. The process by which TurboVNC does this is referred to as an "encoding method." A rectangle is first analyzed to determine if any significant portion of it is solid, and if so, that portion is encoded as a bounding box and a fill color ("Solid subencoding.") Of the remaining subrectangles, those with only two colors are encoded as a 1-bit-per-pixel bitmap with a 2-color palette ("Mono subencoding"), those with low numbers of unique colors are encoded as a color palette and an 8-bit-per-pixel bitmap ("Indexed color subencoding"), and subrectangles with high numbers of unique colors are encoded using either JPEG or arrays of RGB pixels ("Raw subencoding"), depending on the encoding method. zlib can optionally be used to compress the indexed color, mono and raw subrectangles.

Part of TurboVNC's speedup comes from the use of libjpeg-turbo, a SIMD-accelerated JPEG codec. However, TurboVNC also eliminates the CPU-hungry smoothness detection routines that TightVNC uses to determine whether a subrectangle is a good candidate for JPEG compression, and TurboVNC's encoding methods tend to favor the use of JPEG more, since it is now generally the fastest subencoding type. Furthermore, TurboVNC eliminates buffer copies, it maximizes network efficiency by splitting framebuffer updates into relatively large subrectangles, and it uses only the zlib compression levels that can be shown to have a measurable performance benefit.

TurboVNC is the product of extensive research, in which many different permutations of the TightVNC encoder were benchmarked at the low level against a variety of RFB session captures that simulate real-world application workloads, both 2D and 3D. TurboVNC's encoding methods have been adopted by TigerVNC, LibVNC, UltraVNC, and other projects.

TurboVNC, when used with VirtualGL, provides a highly performant and robust solution for remotely displaying 3D applications over all types of networks.

On "modern" hardware, TurboVNC is capable of streaming 50+ Megapixels/second over a 100 Megabit/second local area network with perceptually lossless image quality. TurboVNC can stream between 10 and 12 Megapixels/second over a 5 Megabit/second broadband connection at reduced (but usable) image quality.

TurboVNC is compatible with other VNC distributions, particularly those that also support Tight encoding (such as TigerVNC, TightVNC, and UltraVNC.)