internal/graphicsdriver/opengl: introduce EBITENGINE_OPENGL replacing ebitenginewebgl1

This change inroduces a new environment variable `EBITENGINE_OPENGL`
to replace the build tag `ebitenginewebgl1`.

.github/workflows/test.yml

@@ -129,7 +129,7 @@ jobs:
         if: ${{ !startsWith(matrix.os, 'windows-') && !startsWith(matrix.go, '1.15.') && !startsWith(matrix.go, '1.16.') }}
         run: |
           env GOOS=js GOARCH=wasm go test -tags=example ${{ !startsWith(matrix.go, '1.15.') && !startsWith(matrix.go, '1.16.') && '-shuffle=on' || '' }} -v ./...
-          env GOOS=js GOARCH=wasm go test -tags=example,ebitenginewebgl1 ${{ !startsWith(matrix.go, '1.15.') && !startsWith(matrix.go, '1.16.') && '-shuffle=on' || '' }} -v ./...
+          env GOOS=js GOARCH=wasm EBITENGINE_OPENGL=webgl1 go test -tags=example ${{ !startsWith(matrix.go, '1.15.') && !startsWith(matrix.go, '1.16.') && '-shuffle=on' || '' }} -v ./...
 
       - name: Install ebitenmobile
         run: |

doc.go

@@ -81,13 +81,16 @@
 //	"warp":  Use WARP (i.e. software rendering).
 //	"debug": Use a debug layer.
 //
+// `EBITENGINE_OPENGL` environment variable specifies various parameters for OpenGL.
+// You can specify multiple values separated by a comma. The default value is empty (i.e. no parameters).
+//
+//	"webgl1": Use WebGL 1. This is valid only on browsers.
+//
 // # Build tags
 //
 // `ebitenginedebug` outputs a log of graphics commands. This is useful to know what happens in Ebitengine. In general, the
 // number of graphics commands affects the performance of your game.
 //
-// `ebitenginewebgl1` forces to use WebGL 1 on browsers.
-//
 // `ebitenginesinglethread` disables Ebitengine's thread safety to unlock maximum performance. If you use this you will have
 // to manage threads yourself. Functions like IsKeyPressed will no longer be concurrent-safe with this build tag.
 // They must be called from the main thread or the same goroutine as the given game's callback functions like Update

internal/graphicsdriver/opengl/context_js.go

@@ -17,6 +17,8 @@ package opengl
 import (
 	"errors"
 	"fmt"
+	"os"
+	"strings"
 	"syscall/js"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
@@ -95,9 +97,16 @@ const (
 	webGLVersion2
 )
 
-var (
+func webGL2MightBeAvailable() bool {
-	webGL2MightBeAvailable = !forceWebGL1 && (js.Global().Get("WebGL2RenderingContext").Truthy())
+	env := os.Getenv("EBITENGINE_OPENGL")
-)
+	for _, t := range strings.Split(env, ",") {
+		switch strings.TrimSpace(t) {
+		case "webgl1":
+			return false
+		}
+	}
+	return js.Global().Get("WebGL2RenderingContext").Truthy()
+}
 
 func uint8ArrayToSlice(value js.Value, length int) []byte {
 	if l := value.Get("byteLength").Int(); length > l {
@@ -131,7 +140,7 @@ func (c *context) initGL() error {
 		attr.Set("premultipliedAlpha", true)
 		attr.Set("stencil", true)
 
-		if webGL2MightBeAvailable {
+		if webGL2MightBeAvailable() {
 			gl = canvas.Call("getContext", "webgl2", attr)
 			if gl.Truthy() {
 				c.webGLVersion = webGLVersion2

internal/graphicsdriver/opengl/context_notwebgl1.go

@@ -1,20 +0,0 @@
-// 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.
-
-//go:build !ebitenginewebgl1 && !ebitenwebgl1
-// +build !ebitenginewebgl1,!ebitenwebgl1
-
-package opengl
-
-const forceWebGL1 = false

internal/graphicsdriver/opengl/context_webgl1.go

@@ -1,20 +0,0 @@
-// 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.
-
-//go:build ebitenginewebgl1 || ebitenwebgl1
-// +build ebitenginewebgl1 ebitenwebgl1
-
-package opengl
-
-const forceWebGL1 = true