Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Replace TightVNC encoder with TurboVNC encoder. This patch is the res…
…ult of further research and discussion that revealed the following: -- TightPng encoding and the rfbTightNoZlib extension need not conflict. Since TightPng is a separate encoding type, not supported by TurboVNC-compatible viewers, then the rfbTightNoZlib extension can be used solely whenever the encoding type is Tight and disabled with the encoding type is TightPng. -- In the TightVNC encoder, compression levels above 5 are basically useless. On the set of 20 low-level datasets that were used to design the TurboVNC encoder (these include the eight 2D application captures that were also used when designing the TightVNC encoder, as well as 12 3D application captures provided by the VirtualGL Project-- see http://www.virtualgl.org/pmwiki/uploads/About/tighttoturbo.pdf), moving from Compression Level (CL) 5 to CL 9 in the TightVNC encoder did not increase the compression ratio of any datasets more than 10%, and the compression ratio only increased by more than 5% on four of them. The compression ratio actually decreased a few percent on five of them. In exchange for this paltry increase in compression ratio, the CPU usage, on average, went up by a factor of 5. Thus, for all intents and purposes, TightVNC CL 5 provides the "best useful compression" for that encoder. -- TurboVNC's best compression level (CL 2) compresses 3D and video workloads significantly more "tightly" than TightVNC CL 5 (~70% better, in the aggregate) but does not quite achieve the same level of compression with 2D workloads (~20% worse, in the aggregate.) This decrease in compression ratio may or may not be noticeable, since many of the datasets it affects are not performance-critical (such as the console output of a compilation, etc.) However, for peace of mind, it was still desirable to have a mode that compressed with equal "tightness" to TightVNC CL 5, since we proposed to replace that encoder entirely. -- A new mode was discovered in the TurboVNC encoder that produces, in the aggregate, similar compression ratios on 2D datasets as TightVNC CL 5. That new mode involves using Zlib level 7 (the same level used by TightVNC CL 5) but setting the "palette threshold" to 256, so that indexed color encoding is used whenever possible. This mode reduces bandwidth only marginally (typically 10-20%) relative to TurboVNC CL 2 on low-color workloads, in exchange for nearly doubling CPU usage, and it does not benefit high-color workloads at all (since those are usually encoded with JPEG.) However, it provides a means of reproducing the same "tightness" as the TightVNC encoder on 2D workloads without sacrificing any compression for 3D/video workloads, and without using any more CPU time than necessary. -- The TurboVNC encoder still performs as well or better than the TightVNC encoder when plain libjpeg is used instead of libjpeg-turbo. Specific notes follow: common/turbojpeg.c common/turbojpeg.h: Added code to emulate the libjpeg-turbo colorspace extensions, so that the TurboJPEG wrapper can be used with plain libjpeg as well. This required updating the TurboJPEG wrapper to the latest code from libjpeg-turbo 1.2.0, mainly because the TurboJPEG 1.2 API handles pixel formats in a much cleaner way, which made the conversion code easier to write. It also eases the maintenance to have the wrapper synced as much as possible with the upstream code base (so I can merge any relevant bug fixes that are discovered upstream.) The libvncserver version of the TurboJPEG wrapper is a "lite" version, containing only the JPEG compression/decompression code and not the lossless transform, YUV encoding/decoding, and dynamic buffer allocation features from TurboJPEG 1.2. configure.ac: Removed the --with-turbovnc option. configure still checks for the presence of libjpeg-turbo, but only for the purposes of printing a performance warning if it isn't available. rfb/rfb.h: Fix a bug introduced with the initial TurboVNC encoder patch. We cannot use tightQualityLevel for the TurboVNC 1-100 quality level, because tightQualityLevel is also used by ZRLE. Thus, a new parameter (turboQualityLevel) was created. rfb/rfbproto.h: Remove TurboVNC-specific #ifdefs and language libvncserver/rfbserver.c: Remove TurboVNC-specific #ifdefs. Fix afore-mentioned tightQualityLevel bug. libvncserver/tight.c: Replaced the TightVNC encoder with the TurboVNC encoder. Relative to the initial TurboVNC encoder patch, this patch also: -- Adds TightPng support to the TurboVNC encoder -- Adds the afore-mentioned low-bandwidth mode, which is mapped externally to Compression Level 9 test/*: Included TJUnitTest (a regression test for the TurboJPEG wrapper) as well as TJBench (a benchmark for same.) These are useful for ensuring that the wrapper still functions correctly and performantly if it needs to be modified for whatever reason. Both of these programs are derived from libjpeg-turbo 1.2.0. As with the TurboJPEG wrapper, they do not contain the more advanced features of TurboJPEG 1.2, such as YUV encoding/decoding and lossless transforms.
- Loading branch information
1 parent
5f2794f
commit 7124b5f