internal/gamepaddb: allow the standard layout mapping for any platforms

Closes #1957

input.go

@@ -304,6 +304,15 @@ func IsStandardGamepadLayoutAvailable(id GamepadID) bool {
 // When using this facility to support new hardware, please also send a pull request to
 // https://github.com/gabomdq/SDL_GameControllerDB to make your mapping available to everyone else.
 //
+// A platform field in a line corresponds with a GOOS like the following:
+//
+//    "Windows":  GOOS=windows
+//    "Mac OS X": GOOS=darwin (not ios)
+//    "Linux":    GOOS=linux (not android)
+//    "Android":  GOOS=android
+//    "iOS":      GOOS=ios
+//    "":         Any GOOS
+//
 // On platforms where gamepad mappings are not managed by Ebiten, this always returns false and nil.
 //
 // UpdateStandardGamepadLayoutMappings is concurrent-safe.

internal/gamepaddb/gamepaddb.go

@@ -145,6 +145,8 @@ func processLine(line string, platform platform) error {
 			continue
 		}
 		tks := strings.Split(token, ":")
+
+		// Note that the platform part is listed in the definition of SDL_GetPlatform.
 		if tks[0] == "platform" {
 			switch tks[1] {
 			case "Windows":
@@ -167,6 +169,8 @@ func processLine(line string, platform platform) error {
 				if platform != platformIOS {
 					return nil
 				}
+			case "":
+				// Allow any platforms
 			default:
 				return fmt.Errorf("gamepaddb: unexpected platform: %s", tks[1])
 			}
@@ -503,10 +507,6 @@ func IsButtonPressed(id string, button StandardButton, state GamepadState) bool
 // Update adds new gamepad mappings.
 // The string must be in the format of SDL_GameControllerDB.
 func Update(mapping []byte) (bool, error) {
-	if currentPlatform == platformUnknown {
-		return false, nil
-	}
-
 	mappingsM.Lock()
 	defer mappingsM.Unlock()