add new environment variables with the EBITENGINE_ suffix

Updates #2111
Updates #2190

doc.go

@@ -56,16 +56,16 @@
 //
 // Environment variables
 //
-// `EBITEN_SCREENSHOT_KEY` environment variable specifies the key
+// `EBITENGINE_SCREENSHOT_KEY` environment variable specifies the key
 // to take a screenshot. For example, if you run your game with
-// `EBITEN_SCREENSHOT_KEY=q`, you can take a game screen's screenshot
+// `EBITENGINE_SCREENSHOT_KEY=q`, you can take a game screen's screenshot
 // by pressing Q key. This works only on desktops.
 //
-// `EBITEN_INTERNAL_IMAGES_KEY` environment variable specifies the key
+// `EBITENGINE_INTERNAL_IMAGES_KEY` environment variable specifies the key
 // to dump all the internal images. This is valid only when the build tag
 // 'ebitendebug' is specified. This works only on desktops.
 //
-// `EBITEN_GRAPHICS_LIBRARY` environment variable specifies the graphics library.
+// `EBITENGINE_GRAPHICS_LIBRARY` environment variable specifies the graphics library.
 // If the specified graphics library is not available, RunGame returns an error.
 // This can take one of the following value:
 //
@@ -74,7 +74,7 @@
 //     "directx": DirectX. This works only on Windows.
 //     "metal":   Metal. This works only on macOS or iOS.
 //
-// `EBITEN_DIRECTX` environment variable specifies various parameters for DirectX.
+// `EBITENGINE_DIRECTX` environment variable specifies various parameters for DirectX.
 // You can specify multiple values separated by a comma. The default value is empty (i.e. no parameters).
 //
 //     "warp":  Use WARP (i.e. software rendering).

imagedumper_desktop.go

@@ -98,16 +98,27 @@ type imageDumper struct {
 	err error
 }
 
+func envScreenshotKey() string {
+	if env := os.Getenv("EBITENGINE_SCREENSHOT_KEY"); env != "" {
+		return env
+	}
+	// For backward compatibility, read the EBITEN_ version.
+	return os.Getenv("EBITEN_SCREENSHOT_KEY")
+}
+
+func envInternalImagesKey() string {
+	if env := os.Getenv("EBITENGINE_INTERNAL_IMAGES_KEY"); env != "" {
+		return env
+	}
+	// For backward compatibility, read the EBITEN_ version.
+	return os.Getenv("EBITEN_INTERNAL_IMAGES_KEY")
+}
+
 func (i *imageDumper) update() error {
 	if i.err != nil {
 		return i.err
 	}
 
-	const (
-		envScreenshotKey     = "EBITEN_SCREENSHOT_KEY"
-		envInternalImagesKey = "EBITEN_INTERNAL_IMAGES_KEY"
-	)
-
 	if err := i.g.Update(); err != nil {
 		return err
 	}
@@ -116,14 +127,14 @@ func (i *imageDumper) update() error {
 	if i.keyState == nil {
 		i.keyState = map[Key]int{}
 
-		if keyname := os.Getenv(envScreenshotKey); keyname != "" {
+		if keyname := envScreenshotKey(); keyname != "" {
 			if key, ok := keyNameToKeyCode(keyname); ok {
 				i.hasScreenshotKey = true
 				i.screenshotKey = key
 			}
 		}
 
-		if keyname := os.Getenv(envInternalImagesKey); keyname != "" {
+		if keyname := envInternalImagesKey(); keyname != "" {
 			if isDebug {
 				if key, ok := keyNameToKeyCode(keyname); ok {
 					i.hasDumpInternalImagesKey = true

internal/graphicsdriver/directx/graphics_windows.go

@@ -152,7 +152,12 @@ func (g *Graphics) initialize() (ferr error) {
 		useWARP       bool
 		useDebugLayer bool
 	)
-	for _, t := range strings.Split(os.Getenv("EBITEN_DIRECTX"), ",") {
+	env := os.Getenv("EBITENGINE_DIRECTX")
+	if env == "" {
+		// For backward compatibility, read the EBITEN_ version.
+		env = os.Getenv("EBITEN_DIRECTX")
+	}
+	for _, t := range strings.Split(env, ",") {
 		switch strings.TrimSpace(t) {
 		case "warp":
 			// TODO: Is WARP available on Xbox?

internal/ui/graphics.go

@@ -29,9 +29,15 @@ type graphicsDriverCreator interface {
 }
 
 func newGraphicsDriver(creator graphicsDriverCreator) (graphicsdriver.Graphics, error) {
-	const envName = "EBITEN_GRAPHICS_LIBRARY"
+	envName := "EBITENGINE_GRAPHICS_LIBRARY"
+	env := os.Getenv(envName)
+	if env == "" {
+		// For backward compatibility, read the EBITEN_ version.
+		envName = "EBITEN_GRAPHICS_LIBRARY"
+		env = os.Getenv(envName)
+	}
 
-	switch env := os.Getenv(envName); env {
+	switch env {
 	case "", "auto":
 		g, err := creator.newAuto()
 		if err != nil {