iOS/MacOS:Refactor metal rendering by extracting common implementation

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/RTCLogging.h"
 #import "WebRTC/RTCVideoFrame.h"
 
+#import "RTCMTLI420Renderer.h"
 #import "RTCMTLNV12Renderer.h"
 
 // To avoid unreconized symbol linker errors, we're taking advantage of the objc runtime.
 // Linking errors occur when compiling for architectures that don't support Metal.
 #define MTKViewClass NSClassFromString(@"MTKView")
 #define RTCMTLNV12RendererClass NSClassFromString(@"RTCMTLNV12Renderer")
+#define RTCMTLI420RendererClass NSClassFromString(@"RTCMTLI420Renderer")
 
 @interface RTCMTLVideoView () <MTKViewDelegate>
-@property(nonatomic, strong) RTCMTLNV12Renderer *renderer;
+@property(nonatomic, strong) RTCMTLI420Renderer *rendererI420;
+@property(nonatomic, strong) RTCMTLNV12Renderer *rendererNV12;
 @property(nonatomic, strong) MTKView *metalView;
 @property(atomic, strong) RTCVideoFrame *videoFrame;
 @end
 
 @implementation RTCMTLVideoView
 
-@synthesize renderer = _renderer;
+@synthesize rendererI420 = _rendererI420;
+@synthesize rendererNV12 = _rendererNV12;
 @synthesize metalView = _metalView;
 @synthesize videoFrame = _videoFrame;
 
 - (instancetype)initWithFrame:(CGRect)frameRect {
   self = [super initWithFrame:frameRect];
   if (self) {
     [self configure];
   }
   return self;
 }
@@ skipping 14 matching lines @@
 #else
   return NO;
 #endif
 }
 
 + (MTKView *)createMetalView:(CGRect)frame {
   MTKView *view = [[MTKViewClass alloc] initWithFrame:frame];
   return view;
 }
 
-+ (RTCMTLNV12Renderer *)createMetalRenderer {
++ (RTCMTLNV12Renderer *)createNV12Renderer {
   RTCMTLNV12Renderer *renderer = [[RTCMTLNV12RendererClass alloc] init];

[magjed_webrtc, 2017/04/04 08:07:36]

nit: Maybe just return the result directly?

   return renderer;
 }
 
++ (RTCMTLI420Renderer *)createI420Renderer {
+  RTCMTLI420Renderer *renderer = [[RTCMTLI420RendererClass alloc] init];
+  return renderer;
+}
+
 - (void)configure {
   if (![RTCMTLVideoView isMetalAvailable]) {
     RTCLog("Metal unavailable");
     return;
   }
 
   _metalView = [RTCMTLVideoView createMetalView:self.bounds];
-  _renderer = [RTCMTLVideoView createMetalRenderer];
+  _rendererI420 = [RTCMTLVideoView createI420Renderer];

[magjed_webrtc, 2017/04/04 08:07:36]

Are these expensive to set up? If they are, we could do it lazily instead based
on self.videoFrame.nativeHandle, since we will either only receive I420 or NV12
frames (unlikely that the source provides mixed formats).

[daniela-webrtc, 2017/04/05 11:49:31]

Sadly the configuration is quite expensive and entails setup of the buffers,
texture caches, loading of shader programs and setup of command encoders. 

[magjed_webrtc, 2017/04/05 12:10:38]

Ok, so can we try to move the configuration of the shaders to renderFrame on the
first arrival of a frame?

+  _rendererNV12 = [RTCMTLVideoView createNV12Renderer];
 
-  if ([self configureMetalRenderer]) {
+  if ([self configureMetalRenderers]) {
     [self configureMetalView];
   } else {
-    _renderer = nil;
     RTCLogError("Metal configuration falied.");
   }
 }
 
-- (BOOL)configureMetalRenderer {
-  return [_renderer addRenderingDestination:_metalView];
+- (BOOL)configureMetalRenderers {
+  if (![_rendererI420 addRenderingDestination:_metalView]) {
+    _rendererI420 = nil;
+  }
+
+  if (![_rendererNV12 addRenderingDestination:_metalView]) {
+    _rendererNV12 = nil;
+  }
+  return _rendererNV12 || _rendererI420;
 }
 
 - (void)configureMetalView {
   if (_metalView) {
     _metalView.delegate = self;
     [self addSubview:_metalView];
     _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;
   }
 }
 
 #pragma mark - MTKViewDelegate methods
 
 - (void)drawInMTKView:(nonnull MTKView *)view {
   NSAssert(view == self.metalView, @"Receiving draw callbacks from foreign instance.");
-  [self.renderer drawFrame:self.videoFrame];
+  if (!self.videoFrame) {
+    return;
+  }
+
+  if (self.videoFrame.nativeHandle) {
+    [self.rendererNV12 drawFrame:self.videoFrame];
+  } else {
+    [self.rendererI420 drawFrame:self.videoFrame];
+  }
 }
 
 - (void)mtkView:(MTKView *)view drawableSizeWillChange:(CGSize)size {
 }
 
 #pragma mark - RTCVideoRenderer
 
 - (void)setSize:(CGSize)size {
   self.metalView.drawableSize = size;
   [self.metalView draw];
 }
 
 - (void)renderFrame:(nullable RTCVideoFrame *)frame {
   if (frame == nil) {
     RTCLogInfo(@"Incoming frame is nil. Exiting render callback.");
     return;
   }
   self.videoFrame = frame;
 }
 
 @end