ui: SwapBuffer is now done on the rendering context thread

internal/graphics/opengl/context.go

@@ -47,12 +47,14 @@ func GetProgramID(p Program) ProgramID {
 	return ProgramID(p.Value)
 }
 
-type context struct{}
-
-// TODO: These variables can be in the context struct.
-var (
-	gl     mgl.Context
+type context struct {
 	worker mgl.Worker
+	funcs  chan func()
+}
+
+// TODO: This variable can be in the context struct.
+var (
+	gl mgl.Context
 )
 
 func NewContext() *Context {
@@ -68,14 +70,19 @@ func NewContext() *Context {
 		Triangles:          mgl.TRIANGLES,
 		Lines:              mgl.LINES,
 	}
-	gl, worker = mgl.NewContext()
+	c.funcs = make(chan func())
+	gl, c.worker = mgl.NewContext()
 	return c
 }
 
-func Loop() {
+func (c *Context) Loop() {
 	for {
-		<-worker.WorkAvailable()
-		worker.DoWork()
+		select {
+		case <-c.worker.WorkAvailable():
+			c.worker.DoWork()
+		case f := <-c.funcs:
+			f()
+		}
 	}
 }
 
@@ -88,6 +95,16 @@ func (c *Context) Init() {
 	gl.BlendFunc(mgl.ONE, mgl.ONE_MINUS_SRC_ALPHA)
 }
 
+func (c *Context) RunOnContextThread(f func()) {
+	ch := make(chan struct{})
+	c.funcs <- func() {
+		f()
+		close(ch)
+	}
+	<-ch
+	return
+}
+
 func (c *Context) Check() {
 	if e := gl.GetError(); e != mgl.NO_ERROR {
 		panic(fmt.Sprintf("check failed: %d", e))

internal/ui/ui_glfw.go

@@ -57,15 +57,15 @@ func Init() *opengl.Context {
 		runtime.LockOSThread()
 		u.window.MakeContextCurrent()
 		glfw.SwapInterval(1)
+		u.context = opengl.NewContext()
 		close(ch)
-		opengl.Loop()
+		u.context.Loop()
 	}()
 	currentUI = u
-	context := opengl.NewContext()
 	<-ch
-	context.Init()
+	u.context.Init()
 
-	return context
+	return u.context
 }
 
 func Start(width, height, scale int, title string) (actualScale int, err error) {
@@ -104,6 +104,7 @@ type userInterface struct {
 	height      int
 	scale       int
 	actualScale int
+	context     *opengl.Context
 }
 
 func (u *userInterface) start(width, height, scale int, title string) (actualScale int, err error) {
@@ -146,7 +147,9 @@ func (u *userInterface) isClosed() bool {
 }
 
 func (u *userInterface) swapBuffers() {
-	u.window.SwapBuffers()
+	u.context.RunOnContextThread(func() {
+		u.window.SwapBuffers()
+	})
 }
 
 func (u *userInterface) setScreenSize(width, height, scale int) bool {