gpu,app/internal/wm: add Metal port

The OpenGL (ES) implementations on Apple platforms are deprecated and
don't support GPU compute programs. This change adds support for the
replacement, the Metal GPU API.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/internal/wm/metal_ios.go

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+//go:build !nometal
+// +build !nometal
+
+package wm
+
+/*
+#cgo CFLAGS: -Werror -xobjective-c -fmodules -fobjc-arc
+
+@import UIKit;
+
+@import QuartzCore.CAMetalLayer;
+
+#include <CoreFoundation/CoreFoundation.h>
+
+Class gio_layerClass(void) {
+	return [CAMetalLayer class];
+}
+
+static CFTypeRef getMetalLayer(CFTypeRef viewRef) {
+	@autoreleasepool {
+		UIView *view = (__bridge UIView *)viewRef;
+		return CFBridgingRetain(view.layer);
+	}
+}
+
+static void resizeDrawable(CFTypeRef viewRef, CFTypeRef layerRef) {
+	@autoreleasepool {
+		UIView *view = (__bridge UIView *)viewRef;
+		CAMetalLayer *layer = (__bridge CAMetalLayer *)layerRef;
+		layer.contentsScale = view.contentScaleFactor;
+		CGSize size = layer.bounds.size;
+		size.width *= layer.contentsScale;
+		size.height *= layer.contentsScale;
+		layer.drawableSize = size;
+	}
+}
+*/
+import "C"
+
+func getMetalLayer(view C.CFTypeRef) C.CFTypeRef {
+	return C.getMetalLayer(view)
+}
+
+func resizeDrawable(view, layer C.CFTypeRef) {
+	C.resizeDrawable(view, layer)
+}