Special K: New "Latent Sync" Limiter [Better than RTSS Scanline Sync]
Posted: 21 Nov 2021, 00:47
Introduction
In 2018, RTSS added a new framerate limiter mode called Scanline Sync to steer the tearline off-screen while VSYNC is off.
RTSS Scanline Sync has a number of limitations that we believe have limited its appeal and adoption, none the least of which RTSS is a closed source product that cannot be studied, improved or integrated directly into other software projects. Further, RTSS lacks important low-level overrides (it cannot actually turn VSYNC off -- a pre-requisite for Scanline Sync to even work...)
Special K takes a different approach. It has been open source since 2015, and was purpose-built to expose and override render settings that Windows and graphics drivers hide from users!
In 2021, Special K released an open source alternative to Scanline Sync.
What is Latent Sync?
Latent Sync is collection of advanced framerate limiting features for VSYNC off rendering.
In its initial implementation (November 2021), Latent Sync offers a complete replacement for Scanline Sync in D3D9/11/12 and OpenGL (Vulkan support planned in 2022). In addition to "lagless VSYNC", the new limiter mode also implements experimental software-based Black Frame Insertion in OpenGL and D3D11.
What is New in Latent Sync?
Solved Limitations of Prior "Lagless VSYNC" Implementations
1. Special K will convert all D3D11 borderless fullscreen modes into the proper optimized substitute for fullscreen exclusive ("Hardware Independent Flip"). This is the same mode that D3D12 games use and is the reason Microsoft was able to completely eliminate Fullscreen Exclusive from D3D12.
2. Special K has a number of multi-monitor features, including per-game monitor assignment. It has no trouble detecting which monitor a game is running on and detects changes to signal timing and display config in real-time.
3. Special K has full control over VSYNC in OpenGL, D3D9, D3D11 and D3D12. It automatically applies the correct VSYNC settings, including the special DWM tearing flag necessary to turn VSYNC off in windowed mode!
Performance Tuning
All configuration is done in-game using SK's overlay, the Latent Sync menu shown is accessed by right-clicking the framerate limit slider.
... PresentMon Integration
A brief word on Presentation Models as they relate to VSYNC and latency since there is a ton of confusion on this topic in these forums.
Latent Sync works with the following modes (these bypass the DWM and VSYNC can be disabled):
Future Development
Special K currently lacks support for Vulkan, a Vulkan layer is planned for 2022 but is not a top priority.
Anti-cheat also prevents using SK in some games and this will be addressed with the release of a standalone library (MIT license) that implements all of SK's framerate limiter (sans render API overrides such as flip model and PresentMon). A few anti-cheat games have committed to adopting this library, and it is also hoped that anti-cheat whitelisted projects (i.e. ReShade 5.0) will offer the limiter to users.
Black Frame Insertion, while not directly related to latency, is also a key development focus moving forward. Perfecting this new limiter will open doors for software-based BFI.
Download and Discuss
The latest version of Special K (SpecialK_21.10.22.exe) including Latent Sync is available on our Discord server, in the #releases channel https://discord.gg/SpecialK.
The Wiki (https://wiki.special-k.info) is currently being updated with a guide for configuring Latent Sync, we expect this should be familiar to anyone who has used RTSS Scanline Sync and are looking for feedback while finishing the documentation.
In 2018, RTSS added a new framerate limiter mode called Scanline Sync to steer the tearline off-screen while VSYNC is off.
RTSS Scanline Sync has a number of limitations that we believe have limited its appeal and adoption, none the least of which RTSS is a closed source product that cannot be studied, improved or integrated directly into other software projects. Further, RTSS lacks important low-level overrides (it cannot actually turn VSYNC off -- a pre-requisite for Scanline Sync to even work...)
Special K takes a different approach. It has been open source since 2015, and was purpose-built to expose and override render settings that Windows and graphics drivers hide from users!
In 2021, Special K released an open source alternative to Scanline Sync.
What is Latent Sync?
Latent Sync is collection of advanced framerate limiting features for VSYNC off rendering.
In its initial implementation (November 2021), Latent Sync offers a complete replacement for Scanline Sync in D3D9/11/12 and OpenGL (Vulkan support planned in 2022). In addition to "lagless VSYNC", the new limiter mode also implements experimental software-based Black Frame Insertion in OpenGL and D3D11.
What is New in Latent Sync?
Solved Limitations of Prior "Lagless VSYNC" Implementations
- Fullscreen Exclusive is Unnecessary (D3D11/12)
- Supports Multi-Monitor Systems
- Does Not Require Driver/Game VSYNC Settings
1. Special K will convert all D3D11 borderless fullscreen modes into the proper optimized substitute for fullscreen exclusive ("Hardware Independent Flip"). This is the same mode that D3D12 games use and is the reason Microsoft was able to completely eliminate Fullscreen Exclusive from D3D12.
2. Special K has a number of multi-monitor features, including per-game monitor assignment. It has no trouble detecting which monitor a game is running on and detects changes to signal timing and display config in real-time.
3. Special K has full control over VSYNC in OpenGL, D3D9, D3D11 and D3D12. It automatically applies the correct VSYNC settings, including the special DWM tearing flag necessary to turn VSYNC off in windowed mode!
Performance Tuning
- Adaptive Tearing (optional visible tearing if framerate is unstable)
- Bias Pre/Post-Sync Delays (fine-tune frame pacing consistency vs. input latency)
- Built-in Tearing Visualization
All configuration is done in-game using SK's overlay, the Latent Sync menu shown is accessed by right-clicking the framerate limit slider.
- LatentSyncConfig.png (1.04 MiB) Viewed 27498 times
... PresentMon Integration
A brief word on Presentation Models as they relate to VSYNC and latency since there is a ton of confusion on this topic in these forums.
Latent Sync works with the following modes (these bypass the DWM and VSYNC can be disabled):
- Hardware: Independent Flip (Borderless Fullscreen (D3D9/11/12) | Fullscreen Optimization)
- Hardware Composed: Independent Flip (Multiplane Overlay)
- Hardware: Legacy Flip (Fullscreen Exclusive)
- Composed: Flip (Windowed D3D11/12)
- Composed: Copy with GPU GDI (Windowed OpenGL/D3D9/D3D11)
Future Development
Special K currently lacks support for Vulkan, a Vulkan layer is planned for 2022 but is not a top priority.
Anti-cheat also prevents using SK in some games and this will be addressed with the release of a standalone library (MIT license) that implements all of SK's framerate limiter (sans render API overrides such as flip model and PresentMon). A few anti-cheat games have committed to adopting this library, and it is also hoped that anti-cheat whitelisted projects (i.e. ReShade 5.0) will offer the limiter to users.
Black Frame Insertion, while not directly related to latency, is also a key development focus moving forward. Perfecting this new limiter will open doors for software-based BFI.
Download and Discuss
The latest version of Special K (SpecialK_21.10.22.exe) including Latent Sync is available on our Discord server, in the #releases channel https://discord.gg/SpecialK.
The Wiki (https://wiki.special-k.info) is currently being updated with a guide for configuring Latent Sync, we expect this should be familiar to anyone who has used RTSS Scanline Sync and are looking for feedback while finishing the documentation.