ui: Bug fix: gl* method should be called after looping starts

internal/graphics/opengl/context.go

@@ -49,6 +49,12 @@ func GetProgramID(p Program) ProgramID {
 
 type context struct{}
 
+// TODO: These variables can be in the context struct.
+var (
+	gl     mgl.Context
+	worker mgl.Worker
+)
+
 func NewContext() *Context {
 	c := &Context{
 		Nearest:            mgl.NEAREST,
@@ -62,27 +68,21 @@ func NewContext() *Context {
 		Triangles:          mgl.TRIANGLES,
 		Lines:              mgl.LINES,
 	}
-	c.init()
+	gl, worker = mgl.NewContext()
 	return c
 }
 
-var (
-	gl            mgl.Context
-	worker        mgl.Worker
-	workerCreated = make(chan struct{})
-)
-
 func Loop() {
-	<-workerCreated
 	for {
 		<-worker.WorkAvailable()
 		worker.DoWork()
 	}
 }
 
-func (c *Context) init() {
+func (c *Context) Init() {
-	gl, worker = mgl.NewContext()
+	// This initialization must be done after Loop is called.
-	close(workerCreated)
+	// This is why Init is separated from NewContext.
+
 	// Textures' pixel formats are alpha premultiplied.
 	gl.Enable(mgl.BLEND)
 	gl.BlendFunc(mgl.ONE, mgl.ONE_MINUS_SRC_ALPHA)

internal/ui/ui_glfw.go

@@ -32,7 +32,6 @@ func Now() int64 {
 var currentUI *userInterface
 
 func Init() *opengl.Context {
-	// TODO: Is this OK to lock OS thread only for UI?
 	runtime.LockOSThread()
 
 	err := glfw.Init()
@@ -53,16 +52,20 @@ func Init() *opengl.Context {
 	u := &userInterface{
 		window: window,
 	}
+	ch := make(chan struct{})
 	go func() {
 		runtime.LockOSThread()
 		u.window.MakeContextCurrent()
 		glfw.SwapInterval(1)
+		close(ch)
 		opengl.Loop()
 	}()
-
 	currentUI = u
+	context := opengl.NewContext()
+	<-ch
+	context.Init()
 
-	return opengl.NewContext()
+	return context
 }
 
 func Start(width, height, scale int, title string) (actualScale int, err error) {