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 "WebRTC/RTCVideoFrame.h"
+
+#import "RTCMTLNV12Renderer.h"
+
+@interface RTCMTLVideoView () <MTKViewDelegate>
+@property(nonatomic) id<RTCMTLRenderer> renderer;

[tkchin_webrtc, 2017/02/22 00:22:27]

nit: be consistent with doco of strong or not

usually what I do is assume everything is strong since it is the default
behavior (otherwise we have to annotate everything as strong, like the
id<RTCMTLRenderer> above)

[daniela-webrtc, 2017/02/22 14:50:22]

Done.

+@property(nonatomic, strong) MTKView *metalView;
+@property(atomic, strong) RTCVideoFrame *videoFrame;
+@end
+
+@implementation RTCMTLVideoView {
+  id<RTCMTLRenderer> _renderer;
+}
+
+@synthesize renderer = _renderer;
+@synthesize metalView = _metalView;
+@synthesize videoFrame = _videoFrame;
+
+- (instancetype)initWithFrame:(CGRect)frameRect {
+  self = [super initWithFrame:frameRect];
+  if (self) {
+    [self configure];
+  }
+  return self;
+}
+
+- (instancetype)initWithCoder:(NSCoder *)aCoder {
+  self = [super initWithCoder:aCoder];
+  if (self) {
+    [self configure];
+  }
+  return self;
+}
+
+#pragma mark - Private
+
++ (BOOL)isMetalAvailable {
+#if defined(__OBJC__) && COREVIDEO_SUPPORTS_METAL
+  return YES;
+#endif
+  return NO;

[kthelgason, 2017/02/21 08:09:12]

nit: I'd prefer the return NO to be within an else branch of the ifdef.
Otherwise the code might fail to compile with -Wunreachable-code.

[daniela-webrtc, 2017/02/22 14:50:23]

Done.

+}
+
+- (void)configure {
+  if ([RTCMTLVideoView isMetalAvailable]) {
+    _metalView = [[MTKView alloc] initWithFrame:self.bounds];
+    [self addSubview:_metalView];
+    _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;
+    };
+  }
+}

[tkchin_webrtc, 2017/02/22 00:22:27]

if we know at end of configure whether or not it will work, it may be worth
returning nil in the init methods if configure fails
would also be helpful to log warning if metal is unavailable

[daniela-webrtc, 2017/02/22 14:50:23]

UIView's declaration of init explicitly states nonnull is returned :/ Adding
LogError for now. In future the setup would preferably be separated from the
initializer.

+#pragma mark - MTKViewDelegate methods

[tkchin_webrtc, 2017/02/22 00:22:27]

nit: add blank line after pragma

[daniela-webrtc, 2017/02/22 14:50:23]

Done.

+- (void)drawInMTKView:(nonnull MTKView *)view {
+  if (view == self.metalView) {
+    [_renderer drawFrame:self.videoFrame];
+  }

[tkchin_webrtc, 2017/02/22 00:22:27]

If this is an unexpected scenario, feel free to assert (maybe add a DCHECK
equivalent somewhere.

[daniela-webrtc, 2017/02/22 14:50:22]

Done.

+}
+
+- (void)mtkView:(MTKView *)view drawableSizeWillChange:(CGSize)size {
+}
+
+#pragma mark - RTCVideoRenderer
+
+- (void)setSize:(CGSize)size {
+  _metalView.drawableSize = size;
+  [_metalView draw];
+}
+
+- (void)renderFrame:(nullable RTCVideoFrame *)frame {
+  if (frame == nil) {

[tkchin_webrtc, 2017/02/22 00:22:27]

return or draw black?

[daniela-webrtc, 2017/02/22 14:50:22]

That functionality should not be included in the video view IMO. But I added a
LogInfo.

+    return;
+  }
+  self.videoFrame = frame;
+}
+
+@end