iOS: Add interface for injecting custom shaders

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoViewShaderDelegate.h

+/*
+ *  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 <Foundation/Foundation.h>
+
+#import <WebRTC/RTCVideoFrame.h>
+
+#if TARGET_OS_IPHONE
+@class RTCEAGLVideoView;
+typedef RTCEAGLVideoView RTCVideoView;
+#else
+@class RTCNSGLVideoView;
+typedef RTCNSGLVideoView RTCVideoView;
+#endif
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * RTCVideoViewShaderDelegate provides a way for apps to customize the OpenGL(ES) shaders used in
+ * rendering for the RTCEAGLVideoView/RTCNSGLVideoView.
+ */
+RTC_EXPORT
+@protocol RTCVideoViewShaderDelegate

[daniela-webrtc, 2017/05/11 17:31:21]

I'm bit on the fence here if this should be a delegate protocol. Is it necessary
to pass the RTCVideoView in the callback? Is it relevant for the shader?

[magjed_webrtc, 2017/05/25 14:26:45]

Yeah, I need your expertise here - what's the best/conventional way for doing
this in ObjC? The RTCVideoView argument will probably never be relevant, I just
added it because I thought it was customary. What options do I have besides a
delegate protocol in ObjC? I want clients to be able to customize how shading is
done in the VideoView classes.

[daniela-webrtc, 2017/05/26 08:31:18]

I see. If the video view is not relevant, we can ditch the delegate pattern. But
we can still use protocol i.e modify this one.
```
@protocol RTCShading : NSObject
- (void)applyShadingForFrameWithRotation:(RTCVideoRotation)rotation
yPlane:(GLuint)yPlane uPlane:(GLuint)uPlane vPlane:(GLuint)vPlane;
- (void)applyShadingForFrameWithRotation:(RTCVideoRotation)rotation
yPlane:(GLuint)yPlane uvPlane:(GLuint)uvPlane;

```

Then in RTC*VideoView we could have only one shader instance 
 id<RTCShading> *_shader;

and it could be injected via the initializer like it's currently implemented.
The difference would be that we wouldn't need the separate
_defaultShaderDelegate. But instead we could have something like this in the
initializer

```
- (instancetype)initWithFrame:(CGRect)frame shader:(nullable id<RTCShading
*>)shader {
  if (self = [super initWithFrame:frame) {
     _shader = shader ? shader : [[RTCDefaultShader alloc] init];  // We could
ditch the delegate suffix everywhere.
  }
  return self;
}

Let me know if you need further clarification.

[magjed_webrtc, 2017/05/26 12:05:26]

Done.

+
+/** Callback for I420 frames. Each plane is given as a texture. */
+- (void)videoView:(RTCVideoView *)videoView
+    didReceiveFrameWithRotation:(RTCVideoRotation)rotation

[daniela-webrtc, 2017/05/11 17:31:21]

didUpload seems like better naming, but see my previous comment.

+                         yPlane:(GLuint)yPlane
+                         uPlane:(GLuint)uPlane
+                         vPlane:(GLuint)vPlane;
+
+/** Callback for NV12 frames. Each plane is given as a texture. */
+- (void)videoView:(RTCVideoView *)videoView
+    didReceiveFrameWithRotation:(RTCVideoRotation)rotation

[daniela-webrtc, 2017/05/11 17:31:21]

^

+                         yPlane:(GLuint)yPlane
+                        uvPlane:(GLuint)uvPlane;
+
+@end
+
+NS_ASSUME_NONNULL_END