Make Ebiten buildable on the playground environment

Bug: #871

.travis.yml

@@ -49,6 +49,7 @@ script:
   - gjbt github.com/hajimehoshi/ebiten # TODO: Test the subdirectories
   - GOOS=windows GOARCH=amd64 go build -tags example -v github.com/hajimehoshi/ebiten/examples/...
   - GOOS=windows GOARCH=386 go build -tags example -v github.com/hajimehoshi/ebiten/examples/...
+  - CGO_ENABLED=0 go vet github.com/hajimehoshi/ebiten # This is necessary for the Go playground
 
 # - test -z $(gofmt -s -l $GOPATH/src/github.com/hajimehoshi/ebiten)
 

graphics_opengl.go

@@ -12,7 +12,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build !darwin ios js
+// +build android freebsd ios js linux,cgo windows
+
+// As the Go playground tries to compile this with CGO_ENABLED=0 and GOOS=linux, check Cgo on build tags.
 
 package ebiten
 

graphics_playground.go

@@ -0,0 +1,35 @@
+// 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 !darwin
+// +build !freebsd
+// +build !ios
+// +build !js
+// +build !linux,cgo !cgo
+// +build !windows
+
+package ebiten
+
+import (
+	"github.com/hajimehoshi/ebiten/internal/driver"
+)
+
+func graphicsDriver() driver.Graphics {
+	if !isPlayground {
+		panic("ebiten: a graphics driver is not implemented on this environment")
+	}
+	// TODO: Implement this
+	return nil
+}

run.go

@@ -17,6 +17,7 @@ package ebiten
 import (
 	"image"
 	"sync/atomic"
+	"time"
 
 	"github.com/hajimehoshi/ebiten/internal/clock"
 	"github.com/hajimehoshi/ebiten/internal/driver"
@@ -25,6 +26,10 @@ import (
 
 var _ = __EBITEN_REQUIRES_GO_VERSION_1_12_OR_LATER__
 
+// isPlayground indicates whether the current environment is the Go Playground (play.golang.org) or not.
+// The fixed time is explicitly defined. See "About the Playground" at play.golang.org.
+var isPlayground = time.Now().UnixNano() == 1257894000000000000
+
 // TPS represents a default ticks per second, that represents how many times game updating happens in a second.
 const DefaultTPS = 60
 

ui_glfw.go

@@ -12,10 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build darwin freebsd linux windows
+// +build darwin freebsd linux,cgo windows
-// +build !js
 // +build !android
 // +build !ios
+// +build !js
 
 package ebiten
 

ui_playground.go

@@ -0,0 +1,35 @@
+// 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 !darwin
+// +build !freebsd
+// +build !ios
+// +build !js
+// +build !linux,cgo !cgo
+// +build !windows
+
+package ebiten
+
+import (
+	"github.com/hajimehoshi/ebiten/internal/driver"
+)
+
+func uiDriver() driver.UI {
+	if !isPlayground {
+		panic("ebiten: a UI driver is not implemented on this environment")
+	}
+	// TODO: Implement this
+	return nil
+}