Multithreaded GLFW App with multiple Windows Render Problems

main.go

package main

import (
	"fmt"
	"runtime"
	"time"

	"github.com/go-gl/gl/v2.1/gl"
	"github.com/go-gl/glfw/v3.1/glfw"
)

func main() {
	runtime.LockOSThread()
	if err := glfw.Init(); err != nil {
		panic(err)
	}
	glfw.WindowHint(glfw.ContextVersionMajor, 2)
	glfw.WindowHint(glfw.ContextVersionMinor, 1)
	glfw.WindowHint(glfw.Samples, 4)
	if err := gl.Init(); err != nil {
		panic(err)
	}
	// do stuff outside of main goroutine
	go doStuff()

	// run the mainthread loop
	Main()
}

// outside the mainthread goroutine
func doStuff() {
	Window1 := NewWindow("Window 1", 400, 300)
	Window1.Render()

	Window2 := NewWindow("Window 2", 300, 200)
	Window2.Render()

	time.Sleep(time.Second)
	Window3 := NewWindow("Window 3", 200, 100)
	Window3.Render()
}

// ================== main thread ====================
// adapted from: https://github.com/golang/go/wiki/LockOSThread

func Main() {
	// original code:
	// for f := range mainfunc {
	// 	f()
	// }

	// select loop to catch events:
	for {
		select {
		case f := <-mainfunc:
			f()

			//comment out these two lines:
		default:
			glfw.WaitEvents()

		}
	}
}

// buffered channel to make it possible to put a func
// in the chan and then run it with PostEmptyEvent()
var mainfunc = make(chan func(), 1)

func do(f func()) {
	done := make(chan bool, 1)
	mainfunc <- func() {
		f()
		done <- true
	}

	// added to break WaitEvents in Main():
	glfw.PostEmptyEvent()

	<-done
}

// ================= Window functions =================

type Window struct {
	win *glfw.Window
}

func NewWindow(title string, width, height int) *Window {
	var win *glfw.Window
	var err error
	do(func() {
		win, err = glfw.CreateWindow(width, height, title, nil, nil)
		if err != nil {
			panic(err)
		}
		win.MakeContextCurrent()
		win.SetScrollCallback(func(w *glfw.Window, xoff float64, yoff float64) {
			fmt.Printf("Scroll: x: %.1f y: %.1f\n", xoff, yoff)
		})
		gl.ClearColor(0.2, 0.2, 0.2, 1.0)
	})
	return &Window{win}
}

func (w *Window) Render() {
	do(func() {
		w.win.MakeContextCurrent()
		gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
		w.win.SwapBuffers()
	})
}