iOS: Add interface for injecting custom shaders

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoViewShading.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>
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * RTCVideoViewShading provides a way for apps to customize the OpenGL(ES) shaders used in
+ * rendering for the RTCEAGLVideoView/RTCNSGLVideoView.
+ */
+RTC_EXPORT
+@protocol RTCVideoViewShading <NSObject>
+
+/** Callback for I420 frames. Each plane is given as a texture. */
+- (void)applyShadingForFrameWithRotation:(RTCVideoRotation)rotation
+                                  yPlane:(GLuint)yPlane
+                                  uPlane:(GLuint)uPlane
+                                  vPlane:(GLuint)vPlane;
+
+/** Callback for NV12 frames. Each plane is given as a texture. */
+- (void)applyShadingForFrameWithRotation:(RTCVideoRotation)rotation
+                                  yPlane:(GLuint)yPlane
+                                 uvPlane:(GLuint)uvPlane;
+
+@end
+
+NS_ASSUME_NONNULL_END