Fall-back to OpenGL renderer if mac hardware doesn't support Metal

webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m

 /*
  *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 203 matching lines @@
   [_scrollView setTranslatesAutoresizingMaskIntoConstraints:NO];
   [_scrollView setHasVerticalScroller:YES];
   [_scrollView setDocumentView:_logView];
   [self addSubview:_scrollView];
 
 // NOTE (daniela): Ignoring Clang diagonstic here.
 // We're performing run time check to make sure class is available on runtime.
 // If not we're providing sensible default.
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wpartial-availability"
-  if ([RTCMTLNSVideoView class]) {
+  if ([RTCMTLNSVideoView class] && [RTCMTLNSVideoView isMetalAvailable]) {
     _remoteVideoView = [[RTCMTLNSVideoView alloc] initWithFrame:NSZeroRect];
     _localVideoView = [[RTCMTLNSVideoView alloc] initWithFrame:NSZeroRect];
-  } else {
+  }
+#pragma clang diagnostic pop
+  if (_remoteVideoView == nil) {
     NSOpenGLPixelFormatAttribute attributes[] = {
       NSOpenGLPFADoubleBuffer,
       NSOpenGLPFADepthSize, 24,
       NSOpenGLPFAOpenGLProfile,
       NSOpenGLProfileVersion3_2Core,
       0
     };
     NSOpenGLPixelFormat* pixelFormat =
     [[NSOpenGLPixelFormat alloc] initWithAttributes:attributes];
 
     RTCNSGLVideoView* remote =
         [[RTCNSGLVideoView alloc] initWithFrame:NSZeroRect pixelFormat:pixelFormat];
     remote.delegate = self;
     _remoteVideoView = remote;
 
     RTCNSGLVideoView* local =
         [[RTCNSGLVideoView alloc] initWithFrame:NSZeroRect pixelFormat:pixelFormat];
     local.delegate = self;
     _localVideoView = local;
   }
-#pragma clang diagnostic pop
 
   [_remoteVideoView setTranslatesAutoresizingMaskIntoConstraints:NO];
   [self addSubview:_remoteVideoView];
   [_localVideoView setTranslatesAutoresizingMaskIntoConstraints:NO];
   [self addSubview:_localVideoView];
 }
 
 - (void)setupActionItemsView {
   _actionItemsView = [[NSView alloc] initWithFrame:NSZeroRect];
   [_actionItemsView setTranslatesAutoresizingMaskIntoConstraints:NO];
@@ skipping 169 matching lines @@
 }
 
 - (void)disconnect {
   [self resetUI];
   [_captureController stopCapture];
   _captureController = nil;
   [_client disconnect];
 }
 
 @end