internal/ui: separate graphics_ios.go to each archtecture

This change removes the support of 32bit iOS. 32bit iOS is no longer
supported by Go 1.15.

internal/ui/graphics_ios_amd64.go

@@ -0,0 +1,28 @@
+// Copyright 2022 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 ios && !ebitengl && !ebitencbackend
+// +build ios,!ebitengl,!ebitencbackend
+
+package ui
+
+import (
+	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
+	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl"
+)
+
+func Graphics() graphicsdriver.Graphics {
+	// Metal might not be supported on emulators on Intel machines.
+	return opengl.Get()
+}

internal/ui/graphics_ios_arm64.go

@@ -18,21 +18,14 @@
 package ui
 
 import (
-	"fmt"
-	"runtime"
-
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal"
-	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl"
 )
 
 func Graphics() graphicsdriver.Graphics {
-	if runtime.GOARCH == "386" || runtime.GOARCH == "amd64" {
+	g := metal.Get()
-		return opengl.Get()
+	if g == nil {
+		panic("ui: Metal is not available on this iOS device")
 	}
-
+	return g
-	if metal.Get() == nil {
-		panic(fmt.Sprintf("ui: Metal is not available on this iOS device"))
-	}
-	return metal.Get()
 }