Reland of Add Metal video view in AppRTCMobile and metal availability macro.

webrtc/sdk/objc/Framework/Classes/Metal/RTCMTLNV12Renderer.mm

 /*
  *  Copyright 2017 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 221 matching lines @@
 
   id<MTLCommandBuffer> commandBuffer = [_commandQueue commandBuffer];
   commandBuffer.label = commandBufferLabel;
 
   __block dispatch_semaphore_t block_semaphore = _inflight_semaphore;
   [commandBuffer addCompletedHandler:^(id<MTLCommandBuffer> _Nonnull) {
     // GPU work completed.
     dispatch_semaphore_signal(block_semaphore);
   }];
 
-  MTLRenderPassDescriptor *_renderPassDescriptor = _view.currentRenderPassDescriptor;
-  if (_renderPassDescriptor) {  // Valid drawable.
+  MTLRenderPassDescriptor *renderPassDescriptor = _view.currentRenderPassDescriptor;
+  if (renderPassDescriptor) {  // Valid drawable.
     id<MTLRenderCommandEncoder> renderEncoder =
-        [commandBuffer renderCommandEncoderWithDescriptor:_renderPassDescriptor];
+        [commandBuffer renderCommandEncoderWithDescriptor:renderPassDescriptor];
     renderEncoder.label = renderEncoderLabel;
 
     // Set context state.
     [renderEncoder pushDebugGroup:renderEncoderDebugGroup];
     [renderEncoder setRenderPipelineState:_pipelineState];
     [renderEncoder setVertexBuffer:_vertexBuffer offset:_offset * sizeof(float) atIndex:0];
     [renderEncoder setFragmentTexture:_yTexture atIndex:0];
     [renderEncoder setFragmentTexture:_CrCbTexture atIndex:1];
 
     [renderEncoder drawPrimitives:MTLPrimitiveTypeTriangleStrip
                       vertexStart:0
                       vertexCount:4
                     instanceCount:1];
     [renderEncoder popDebugGroup];
     [renderEncoder endEncoding];
 
     [commandBuffer presentDrawable:_view.currentDrawable];
   }
 
   // CPU work is completed, GPU work can be started.
   [commandBuffer commit];
 }
 
 #pragma mark - RTCMTLRenderer
 
 - (void)drawFrame:(RTCVideoFrame *)frame {
-  [self setupTexturesForFrame:frame];
   @autoreleasepool {
-    [self render];
+    if ([self setupTexturesForFrame:frame])
+      [self render];
   }
 }
 
-- (void)setupTexturesForFrame:(nonnull RTCVideoFrame *)frame {
+- (BOOL)setupTexturesForFrame:(nonnull RTCVideoFrame *)frame {
   CVPixelBufferRef pixelBuffer = frame.nativeHandle;
 
   id<MTLTexture> lumaTexture = nil;
   id<MTLTexture> chromaTexture = nil;
   CVMetalTextureRef outTexture = nullptr;
 
   // Luma (y) texture.
   int lumaWidth = CVPixelBufferGetWidthOfPlane(pixelBuffer, 0);
   int lumaHeight = CVPixelBufferGetHeightOfPlane(pixelBuffer, 0);
 
@@ skipping 17 matching lines @@
       lumaHeight / 2, indexPlane, &outTexture);
   if (result == kCVReturnSuccess) {
     chromaTexture = CVMetalTextureGetTexture(outTexture);
   }
   CVBufferRelease(outTexture);
 
   if (lumaTexture != nil && chromaTexture != nil) {
     _yTexture = lumaTexture;
     _CrCbTexture = chromaTexture;
     _offset = offsetForRotation((webrtc::VideoRotation)frame.rotation);
+    return YES;
   }
+  return NO;
 }
 
 @end