reorganized source, added test cases for tuning

src/scene.go

@@ -0,0 +1,27 @@
+package main
+
+import "github.com/hajimehoshi/ebiten/v2"
+
+// Wrapper for  different screens  to be  shown, as  Welcome, Options,
+// About, Menu Level and of course the actual game
+// Scenes are responsible for screen clearing! That way a scene is able
+// to render its content onto the running level, e.g. the options scene
+// etc.
+
+type SceneName int
+
+type Scene interface {
+	SetNext(SceneName)
+	GetNext() SceneName
+	SetPrevious(SceneName)
+	ResetNext()
+	Update() error
+	Draw(screen *ebiten.Image)
+	IsPrimary() bool // if true, this scene will be always drawn
+}
+
+const (
+	Menu = iota // main top level menu
+	Play        // actual playing happens here
+	Options
+)