Separating event polling from the render thread

[decce6]

Summary

Move event polling out of the render thread to improve performance.

Goals

• Improve performance by moving event polling out of the render thread, i.e. the glfwPollEvents() call

Non Goals

• It is not a goal to move anything else off-thread, i.e. no off-thread GL command submission, etc.
• It is not a goal to replace the native libraries of GLFW, or introduce any other native library

Motivation

glfwPollEvents() is slow, especially on Windows. By moving this call out of the render thread, we can improve FPS stability when moving the mouse.

Description

Basically incorporates Ixeris, which does the same optimization for modern versions of Minecraft. I think implementing this in Cleanroom may make more sense than just porting the mod to 1.12.2.

• We will have a "main thread", or an event thread, that polls events. To meet the requirement of every operating system, it needs to be the thread that the game is started on, so the render thread will be started by it.
• The main thread will call glfwPollEvents() periodically
  • it will also check if other threads have requested it to run some GLFW methods (Most GLFW methods are required to be called on the main thread)
• The render thread will no longer need to call glfwPollEvents()
  • it still needs to run some GLFW callbacks, which may be recorded into a queue by the main thread
• To ensure thread safety:
  • Most GLFW methods may not be called from non-main threads, based on the documentation for individual functions
  • GLFW callbacks should run on the render thread
  • Needs discussion: should we take care of these (by transforming org.lwjgl.glfw.GLFW), or should we require developers who use GLFW to take note?

Dependencies

No response

References

No response

Guidelines

• I have and will continue to adhere to the guidelines

[tttsaurus]

Cleanroom is going to migrate to SDL tho

[Desoroxxx]

Doesn’t matter whether it’s SDL or GLFW, a dedicated polling thread should be implemented.

Normally this should be the main thread where you have a separate render and logic thread.

[Desoroxxx]

To elaborate, Windows (and other platforms) don’t have a way to pull events in a truly performant manner, see libsdl-org/SDL#12821