mobile: Enable to compile in non-mobile environments

This was necessary to show API documents on godoc.org and
pkg.go.dev.

mobile/impl_mobile.go

@@ -0,0 +1,25 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build android ios
+
+package mobile
+
+import (
+	"github.com/hajimehoshi/ebiten/mobile/ebitenmobileview"
+)
+
+func setGame(game Game) {
+	ebitenmobileview.SetGame(game)
+}

mobile/impl_notmobile.go

@@ -0,0 +1,22 @@
+// Copyright 2019 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !android
+// +build !ios
+
+package mobile
+
+func setGame(game Game) {
+	panic("mobile: setGame is not implemented in this environment")
+}

mobile/mobile.go

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build android ios
-
 // Package mobile provides functions for mobile platforms (Android and iOS).
 //
 // This package is used when you use `ebitenmobile bind`.
@@ -23,7 +21,6 @@ package mobile
 
 import (
 	"github.com/hajimehoshi/ebiten"
-	"github.com/hajimehoshi/ebiten/mobile/ebitenmobileview"
 )
 
 // Game defines necessary functions for a mobile game.
@@ -49,5 +46,5 @@ type Game interface {
 //
 // SetGame can be called anytime. Until SetGame is called, the game does not start.
 func SetGame(game Game) {
-	ebitenmobileview.SetGame(game)
+	setGame(game)
 }