Minecraft: Bedrock Edition on Windows doesn't opt in for Screen Tearing causing V-Sync Off to not behave correctly.
Examples:
Game FPS capped 2x the refresh rate.
Capped FPS in fullscreen but Uncapped in windowed.
The root issue seems to be how the game is requesting V-Sync to be turned off.
By using PresentMon, a tool that allows us to see performance metrics of a graphical application we can see how IDXGISwapChain::Present() is being called.
Make sure to download their CLI tool & not their installer for PresentMon!
Using the following command in an admin Command Prompt window with gfx_vsync set to 0 disable V-Sync ingame:
presentmon.exe -no_csv -process_name Minecraft.Windows.exeMinecraft: Bedrock Edition internally calls the function as follows:
IDXGISwapChain::Present(0, 0)Technically this does disable V-Sync but as mentioned before it doesn't behave as intended.
[media]My monitor is 75 Hz & as you can see it's capped double the refresh rate.
Microsoft's Documentation for IDXGISwapchain::Present flags specifically mentions DXGI_PRESENT_ALLOW_TEARING must be used in an windowed application to allow for screen tearing as well as the swapchain having screen tearing support via DXGI_SWAP_CHAIN_FLAG_ALLOW_TEARING.
For demonstration purposes, here is the game modded to add screen tearing support.
This is done by:
Hooking IDXGISwapchain::Present(), IDXGISwapchain::ResizeBuffers() & IDXGIFactory2::CreateSwapChainForCoreWindow.
Add screen tearing support via flags as required.
Ā
[media]As you can see as soon as we add screen tearing support, V-Sync works as intended.
Additionally this also fixes MCPE-98861 since V-Sync off works as intended.
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Thank you for your report!
We're tracking this issue in MCPE-110006 and MCPE-166745, so this ticket is being resolved and linked as a duplicate.
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For those you want to try out demonstrated fix, please check out Stonecutter which is available on my GitHub.
I recommend going through the source code for "src/DllMain.c" which contains the V-Sync fix.
I am hopeful Mojang goes out of their way & fixes this V-Sync issue once & for all.