ebitenutil: Seal OpenFile on mobiles

ebitenutil/file.go

@@ -12,7 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build darwin linux windows
 // +build !js
+// +build !android
+// +build !ios
 
 package ebitenutil
 
@@ -23,6 +26,7 @@ import (
 // OpenFile opens a file and returns a stream for its data.
 //
 // This function is available both on desktops and browsers.
+// Note that this doesn't work on mobiles.
 func OpenFile(path string) (ReadSeekCloser, error) {
 	return os.Open(path)
 }

ebitenutil/loadimage.go

@@ -12,6 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build darwin,!arm,!arm64 linux windows
+// +build !android
+// +build !ios
+
 package ebitenutil
 
 import (
@@ -23,6 +27,7 @@ import (
 // NewImageFromFile loads the file path and returns ebiten.Image and image.Image.
 //
 // The current directory for path depends on your environment. This will vary on your desktop or web browser.
+// Note that this doesn't work on browsers.
 // It'll be safer to embed your resource, e.g., with github.com/jteeuwen/go-bindata instead of using this function.
 func NewImageFromFile(path string, filter ebiten.Filter) (*ebiten.Image, image.Image, error) {
 	file, err := OpenFile(path)