iOS/MacOS:Refactor metal rendering by extracting common implementation

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

Index: webrtc/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m
diff --git a/webrtc/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m b/webrtc/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m
index 427ae6c4a1138d4ca0207d8580eef61f5a8499c3..8620ee2bd04dd90bbf77a58431b146f566f7b5e6 100644
--- a/webrtc/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m
+++ b/webrtc/sdk/objc/Framework/Classes/Metal/RTCMTLVideoView.m
@@ -16,22 +16,26 @@
 #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;
 
@@ -66,11 +70,16 @@
   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");
@@ -78,18 +87,25 @@
   }
 
   _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 {
@@ -110,7 +126,15 @@
 
 - (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 {