internal/ui: refactoring: remove dependency on the package mtl

internal/graphicsdriver/metal/graphics_darwin.go

@@ -346,9 +346,24 @@ const (
 	noStencil
 )
 
+// isMetalAvailable reports whether Metal is available or not.
+//
+// On old mac devices like iMac 2011, Metal is not supported (#779).
+var isMetalAvailable bool
+
+func init() {
+	// Initialize isMetalAvailable on the main thread.
+	// TODO: Is there a better way to check whether Metal is available or not?
+	// It seems OK to call MTLCreateSystemDefaultDevice multiple times, so this should be fine.
+	_, isMetalAvailable = mtl.CreateSystemDefaultDevice()
+}
+
 var theGraphics Graphics
 
 func Get() *Graphics {
+	if !isMetalAvailable {
+		return nil
+	}
 	return &theGraphics
 }
 

internal/graphicsdriver/metal/mtl/mtl_darwin.go

@@ -460,10 +460,10 @@ type Device struct {
 // CreateSystemDefaultDevice returns the preferred system default Metal device.
 //
 // Reference: https://developer.apple.com/documentation/metal/1433401-mtlcreatesystemdefaultdevice.
-func CreateSystemDefaultDevice() (Device, error) {
+func CreateSystemDefaultDevice() (Device, bool) {
 	d := C.CreateSystemDefaultDevice()
 	if d.Device == nil {
-		return Device{}, errors.New("Metal is not supported on this system")
+		return Device{}, false
 	}
 
 	return Device{
@@ -471,7 +471,7 @@ func CreateSystemDefaultDevice() (Device, error) {
 		Headless: d.Headless != 0,
 		LowPower: d.LowPower != 0,
 		Name:     C.GoString(d.Name),
-	}, nil
+	}, true
 }
 
 // Device returns the underlying id<MTLDevice> pointer.

internal/graphicsdriver/metal/view_darwin.go

@@ -15,6 +15,7 @@
 package metal
 
 import (
+	"errors"
 	"sync"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal/ca"
@@ -76,10 +77,10 @@ func (v *view) colorPixelFormat() mtl.PixelFormat {
 }
 
 func (v *view) initialize() error {
-	var err error
+	var ok bool
-	v.device, err = mtl.CreateSystemDefaultDevice()
+	v.device, ok = mtl.CreateSystemDefaultDevice()
-	if err != nil {
+	if !ok {
-		return err
+		return errors.New("metal: Metal is not supported")
 	}
 
 	v.ml = ca.MakeMetalLayer()

internal/ui/graphics_darwin.go

@@ -38,24 +38,19 @@ import (
 
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal"
-	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal/mtl"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl"
 )
 
 var graphics graphicsdriver.Graphics
 
 func supportsMetal() bool {
-	// On old mac devices like iMac 2011, Metal is not supported (#779).
-	if _, err := mtl.CreateSystemDefaultDevice(); err != nil {
-		return false
-	}
-
 	// On macOS 10.11 El Capitan, there is a rendering issue on Metal (#781).
 	// Use the OpenGL in macOS 10.11 or older.
 	if C.getMacOSMajorVersion() <= 10 && C.getMacOSMinorVersion() <= 11 {
 		return false
 	}
-	return true
+
+	return metal.Get() != nil
 }
 
 var graphicsOnce sync.Once

internal/ui/graphics_ios.go

@@ -23,7 +23,6 @@ import (
 
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal"
-	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/metal/mtl"
 	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl"
 )
 
@@ -32,8 +31,8 @@ func Graphics() graphicsdriver.Graphics {
 		return opengl.Get()
 	}
 
-	if _, err := mtl.CreateSystemDefaultDevice(); err != nil {
+	if metal.Get() == nil {
-		panic(fmt.Sprintf("mobile: mtl.CreateSystemDefaultDevice failed on iOS: %v", err))
+		panic(fmt.Sprintf("ui: Metal is not available on this iOS device"))
 	}
 	return metal.Get()
 }