Added a theme package

theme/theme.go

@@ -0,0 +1,40 @@
+package theme
+
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/event"
+
+// Role describes the role of an object.
+type Role struct {
+	// Package is an optional namespace field. If specified, it should be
+	// the package name or module name the object is from.
+	Package string
+	
+	// Object specifies what type of object it is. For example:
+	//   - textInput
+	//   - table
+	//   - label
+	//   - dial
+	Object string
+}
+
+// Theme is an object that can apply a visual style to different objects.
+type Theme interface {
+	// Apply applies the theme to the given object, according to the given
+	// role. This may register event listeners with the given object;
+	// closing the returned cookie will remove them.
+	Apply (tomo.Object, Role) event.Cookie
+}
+
+var current Theme
+
+// SetTheme sets the theme.
+func SetTheme (theme Theme) {
+	current = theme
+}
+
+// Apply applies the current theme to the given object, according to the given
+// role. This may register event listeners with the given object; closing the
+// returned cookie will remove them.
+func Apply (object tomo.Object, role Role) event.Cookie {
+	return current.Apply(object, role)
+}