Add metal view, shaders and renderer.

webrtc/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m

+/*
+ *  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.
+ */
+
+#import "WebRTC/RTCMTLVideoView.h"
+
+#import <Metal/Metal.h>
+#import <MetalKit/MetalKit.h>
+
+#import "RTCNV12Renderer.h"
+
+@interface RTCMTLVideoView () <MTKViewDelegate>
+@property(nonatomic) id<RTCMTLRenderer> renderer;
+@property(nonatomic, strong) __kindof UIView *metalView;
+@end
+
+@implementation RTCMTLVideoView {
+  id<RTCMTLRenderer> _renderer;
+}
+
+@synthesize renderer = _renderer;
+@synthesize metalView = _metalView;
+

[tkchin_webrtc, 2017/02/16 23:28:04]

Probably want initWithCoder for all the folks making our view from
nibs/storyboards.

[daniela-webrtc, 2017/02/20 15:17:07]

Done.

+- (instancetype)initWithFrame:(CGRect)frameRect {
+  self = [super initWithFrame:frameRect];
+#if defined(__OBJC__) && COREVIDEO_SUPPORTS_METAL

[tkchin_webrtc, 2017/02/16 23:28:04]

ooc why __OBJC__?

[daniela-webrtc, 2017/02/20 15:17:07]

Metal is available only for ObjectiveC for now.

+  if (self) {
+    _metalView = [[MTKView alloc] initWithFrame:frameRect];
+    [self addSubview:_metalView];
+    ((MTKView *)_metalView).delegate = self;
+    _metalView.contentMode = UIViewContentModeScaleAspectFit;
+    _metalView.translatesAutoresizingMaskIntoConstraints = NO;
+    UILayoutGuide *margins = self.layoutMarginsGuide;
+    [_metalView.topAnchor constraintEqualToAnchor:margins.topAnchor].active = YES;
+    [_metalView.bottomAnchor constraintEqualToAnchor:margins.bottomAnchor].active = YES;
+    [_metalView.leftAnchor constraintEqualToAnchor:margins.leftAnchor].active = YES;
+    [_metalView.rightAnchor constraintEqualToAnchor:margins.rightAnchor].active = YES;
+
+    _renderer = [[RTCNV12Renderer alloc] init];
+    if (![(RTCNV12Renderer *)_renderer addRenderingDestination:_metalView]) {
+      _renderer = nil;
+    };
+  }
+#endif

[tkchin_webrtc, 2017/02/16 23:28:04]

Probably want to return nil if metal isn't supported
may want to add convenience static method to check as well somewhere. Either in
our UIDevice category or as a static method on this class

+ (BOOL)isMetalSupported;

[daniela-webrtc, 2017/02/20 15:17:07]

instancetype is nonnull in the declaration.
Done

+  return self;
+}
+
+- (void)drawInMTKView:(nonnull MTKView *)view {
+  if (view == self.metalView) {
+    [_renderer draw];
+  }
+}
+
+- (void)mtkView:(MTKView *)view drawableSizeWillChange:(CGSize)size {
+}
+@end