graphicsdriver/metal: Use NSAutoreleasePool to release drawable correctly

Fixes #847

internal/driver/graphics.go

@@ -20,6 +20,8 @@ import (
 )
 
 type Graphics interface {
+	Begin()
+	End()
 	SetWindow(window uintptr)
 	SetVertices(vertices []float32, indices []uint16)
 	Flush()

internal/graphicscommand/command.go

@@ -159,6 +159,8 @@ func (q *commandQueue) Flush() {
 	if recordLog() {
 		fmt.Println("--")
 	}
+
+	theGraphicsDriver.Begin()
 	for len(q.commands) > 0 {
 		nv := 0
 		ne := 0
@@ -199,6 +201,7 @@ func (q *commandQueue) Flush() {
 		}
 		q.commands = q.commands[nc:]
 	}
+	theGraphicsDriver.End()
 	q.commands = nil
 	q.nvertices = 0
 	q.nindices = 0

internal/graphicsdriver/metal/driver.go

@@ -30,6 +30,20 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/mainthread"
 )
 
+// #cgo CFLAGS: -x objective-c -mmacosx-version-min=10.11
+// #cgo LDFLAGS: -framework Foundation
+//
+// #import <Foundation/Foundation.h>
+//
+// static void* allocAutoreleasePool() {
+//   return [[NSAutoreleasePool alloc] init];
+// }
+//
+// static void releaseAutoreleasePool(void* pool) {
+//   [(NSAutoreleasePool*)pool release];
+// }
+import "C"
+
 const source = `#include <metal_stdlib>
 
 #define FILTER_NEAREST {{.FilterNearest}}
@@ -287,6 +301,8 @@ type Driver struct {
 	dst *Image
 
 	maxImageSize int
+
+	pool unsafe.Pointer
 }
 
 var theDriver Driver
@@ -295,6 +311,23 @@ func Get() *Driver {
 	return &theDriver
 }
 
+func (d *Driver) Begin() {
+	// NSAutoreleasePool is required to release drawable correctly (#847).
+	// https://developer.apple.com/library/archive/documentation/3DDrawing/Conceptual/MTLBestPracticesGuide/Drawables.html
+	mainthread.Run(func() error {
+		d.pool = C.allocAutoreleasePool()
+		return nil
+	})
+}
+
+func (d *Driver) End() {
+	mainthread.Run(func() error {
+		C.releaseAutoreleasePool(d.pool)
+		d.pool = nil
+		return nil
+	})
+}
+
 func (d *Driver) SetWindow(window uintptr) {
 	mainthread.Run(func() error {
 		// Note that [NSApp mainWindow] returns nil when the window is borderless.

internal/graphicsdriver/opengl/driver.go

@@ -33,6 +33,14 @@ type Driver struct {
 	context context
 }
 
+func (d *Driver) Begin() {
+	// Do nothing.
+}
+
+func (d *Driver) End() {
+	// Do nothing.
+}
+
 func (d *Driver) SetWindow(window uintptr) {
 	// Do nothing.
 }