Add colors

event/event.go

@@ -45,6 +45,10 @@ func (broadcaster *Broadcaster[L]) ensure () {
 	}
 }
 
+// NoCookie is a cookie that does nothing when closed.
+type NoCookie struct { }
+func (NoCookie) Close () { }
+
 type cookie[L any] struct {
 	id int
 	broadcaster *Broadcaster[L]

theme/theme.go

@@ -23,12 +23,24 @@ func R (pack, object string) Role {
 	return Role { Package: pack, Object: object }
 } 
 
+// Color represents a color ID.
+type Color int; const {
+	ColorBackground Color = iota
+	ColorForeground
+	ColorRaised
+	ColorSunken
+	ColorAccent
+}
+
 // 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
+	
+	// Color returns a color for the corresponding color ID.
+	Color (Color) color.Color
 }
 
 var current Theme
@@ -42,5 +54,12 @@ func SetTheme (theme Theme) {
 // 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 {
+	if current == nil { return event.NoCookie { } }
 	return current.Apply(object, role)
 }
+
+// Color returns a color for the corresponding color ID.
+func Color (id Color) color.Color {
+	if current == nil { return color.Black }
+	return current.Color(id)
+}