Introduce 'monogame' build tag experimentally

Updates #1078

doc.go

@@ -96,4 +96,7 @@
 // number of graphics commands affects the performance of your game.
 //
 // `ebitengl` forces to use OpenGL in any environments.
+//
+// `monogame` changes the build target to MonoGame. This must be used with GOOS=js and GOARCH=wasm. This is
+// experimental.
 package ebiten

internal/uidriver/monogame/ui.go

@@ -0,0 +1,106 @@
+// Copyright 2020 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 js
+
+package monogame
+
+import (
+	"github.com/hajimehoshi/ebiten/internal/driver"
+)
+
+type UI struct {
+}
+
+var theUI = &UI{}
+
+func Get() *UI {
+	return theUI
+}
+
+func (*UI) Run(context driver.UIContext) error {
+	return nil
+}
+
+func (*UI) RunWithoutMainLoop(context driver.UIContext) {
+	panic("monogame: RunWithoutMainLoop is not implemented")
+}
+
+func (*UI) DeviceScaleFactor() float64 {
+	return 1
+}
+
+func (*UI) IsFocused() bool {
+	return true
+}
+
+func (*UI) ScreenSizeInFullscreen() (int, int) {
+	// TODO: Implement this
+	return 0, 0
+}
+
+func (*UI) CursorMode() driver.CursorMode {
+	return driver.CursorModeVisible
+}
+
+func (*UI) SetCursorMode(mode driver.CursorMode) {
+	// TODO: Implement this
+}
+
+func (*UI) IsFullscreen() bool {
+	// TODO: Implement this
+	return false
+}
+
+func (*UI) SetFullscreen(fullscreen bool) {
+	// TODO: Implement this
+}
+
+func (*UI) IsRunnableOnUnfocused() bool {
+	// TODO: Implement this
+	return false
+}
+
+func (*UI) SetRunnableOnUnfocused(runnableOnUnfocused bool) {
+	// TODO: Implement this
+}
+
+func (*UI) IsVsyncEnabled() bool {
+	// TODO: Implement this
+	return true
+}
+
+func (*UI) SetVsyncEnabled(enabled bool) {
+	// TODO: Implement this
+}
+
+func (*UI) IsScreenTransparent() bool {
+	return false
+}
+
+func (*UI) SetScreenTransparent(transparent bool) {
+	panic("monogame: SetScreenTransparent is not implemented")
+}
+
+func (*UI) Input() driver.Input {
+	return nil
+}
+
+func (*UI) Window() driver.Window {
+	return nil
+}
+
+func (*UI) Graphics() driver.Graphics {
+	return nil
+}

uidriver_js.go

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build !monogame
 // +build js
 
 package ebiten

uidriver_monogame.go

@@ -0,0 +1,27 @@
+// 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 monogame
+// +build js
+
+package ebiten
+
+import (
+	"github.com/hajimehoshi/ebiten/internal/driver"
+	"github.com/hajimehoshi/ebiten/internal/uidriver/monogame"
+)
+
+func uiDriver() driver.UI {
+	return monogame.Get()
+}