ui: Add comments on Touches

input.go

@@ -107,6 +107,8 @@ type Touch interface {
 }
 
 // Touches returns the current touch states.
+//
+// Touches always returns nil on desktops.
 func Touches() []Touch {
 	t := ui.CurrentInput().Touches()
 	tt := make([]Touch, len(t))

internal/ui/input_glfw.go

@@ -32,7 +32,7 @@ type Input struct {
 	cursorX            int
 	cursorY            int
 	gamepads           [16]gamePad
-	touches            []touch
+	touches            []touch // This is not updated until GLFW 3.3 is available (#417)
 	runeBuffer         []rune
 	m                  sync.RWMutex
 }