how to awake the renderloop when using GLFW.WaitEvents()

[FaresX]

I'm trying to use GLFW.PostEmptyEvent() to trigger the rendering. But when blocked by GLFW.WaitEvents(), it fails to awake the window by other function and only responds to a physical event (mouse or keyboard). For example, this code has no effect

@async while GLFW.WindowShouldClose(CImGui.current_window()) == 0
    GLFW.PostEmptyEvent()
    sleep(0.01)
end

[JamesWrigley]

I would suggest translating this MWE to Julia to verify it works on your system: https://discourse.glfw.org/t/bug-glfwpostemptyevent-does-not-unblock-glfwwaitevents/2079/4
If that works, then you can try figuring out what's wrong in CImGui.

[JamesWrigley]

Possibly dumb question: are you sure the loop is executing at all? By default CImGui will pin itself to thread 1, which is possibly also the thread your loop is running on in which case GLFW.WaitEvents() will block the thread.

[FaresX]

Actually, you're right. When the main thread is blocked by GLFW.WaitEvents(), other threads get blocked as well, so GLFW.PostEmptyEvent() never gets executed. I'm not sure how to work around this issue. One possible solution I can think of is to use GLFW.WaitEvents(timeout) to maintain a minimum framerate.

[FaresX]

I would suggest translating this MWE to Julia to verify it works on your system: https://discourse.glfw.org/t/bug-glfwpostemptyevent-does-not-unblock-glfwwaitevents/2079/4 If that works, then you can try figuring out what's wrong in CImGui.

By the way, this example works.

[JamesWrigley]

If you're on Linux then you can start Julia with multiple threads and run the task with Threads.@spawn instead of @async, the scheduler should then migrate the task to another thread to execute (or you can use StableTasks.jl to pin the task to a specific thread). You'll also want to run ig.render(; spawn=:interactive) or something so that the renderloop isn't pinned to thread 1, see the docs here for the spawn argument: https://juliaimgui.github.io/ImGuiDocs.jl/cimgui/stable/backends/#CImGui.render

[FaresX]

This example works but the window still freezes

import GLFW
import CImGui as ig
import ModernGL as gl

ig.set_backend(:GlfwOpenGL3)

let
    firstframe = true
    Threads.@spawn begin
        sleep(1)
        i = 0
        while !GLFW.WindowShouldClose(ig.current_window())
            @info "post at $(Threads.threadid()) & i = $i"
            GLFW.PostEmptyEvent()
            sleep(0.1)
            i += 1
        end
    end
    ig.render(ig.CreateContext(); window_size=(1280, 760), window_title="ImGui Window", opengl_version=v"3.3", wait_events=true, spawn=2) do
        if firstframe
            @info "run at $(Threads.threadid())"
            firstframe = false
        end
        ig.ShowMetricsWindow(Ref(true))
        yield()
    end
end