iOS: Add support for rendering native CVPixelBuffers directly

webrtc/sdk/objc/Framework/Classes/RTCShader.mm

+/*
+ *  Copyright 2016 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 "RTCShader.h"
+
+#include <memory>
+
+#import "RTCShader+Private.h"
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+
+// Vertex shader doesn't do anything except pass coordinates through.
+const char kRTCVertexShaderSource[] =
+  SHADER_VERSION
+  VERTEX_SHADER_IN " vec2 position;\n"
+  VERTEX_SHADER_IN " vec2 texcoord;\n"
+  VERTEX_SHADER_OUT " vec2 v_texcoord;\n"
+  "void main() {\n"
+  "    gl_Position = vec4(position.x, position.y, 0.0, 1.0);\n"
+  "    v_texcoord = texcoord;\n"
+  "}\n";
+
+// When modelview and projection matrices are identity (default) the world is
+// contained in the square around origin with unit size 2. Drawing to these
+// coordinates is equivalent to drawing to the entire screen. The texture is
+// stretched over that square using texture coordinates (u, v) that range
+// from (0, 0) to (1, 1) inclusive. Texture coordinates are flipped vertically
+// here because the incoming frame has origin in upper left hand corner but
+// OpenGL expects origin in bottom left corner.
+static const GLfloat gVertices[] = {
+  // X, Y, U, V.
+  -1, -1, 0, 1,  // Bottom left.
+   1, -1, 1, 1,  // Bottom right.
+   1,  1, 1, 0,  // Top right.
+  -1,  1, 0, 0,  // Top left.
+};
+
+// Compiles a shader of the given |type| with GLSL source |source| and returns
+// the shader handle or 0 on error.
+GLuint RTCCreateShader(GLenum type, const GLchar *source) {
+  GLuint shader = glCreateShader(type);
+  if (!shader) {
+    return 0;
+  }
+  glShaderSource(shader, 1, &source, NULL);
+  glCompileShader(shader);
+  GLint compileStatus = GL_FALSE;
+  glGetShaderiv(shader, GL_COMPILE_STATUS, &compileStatus);
+  if (compileStatus == GL_FALSE) {
+    GLint logLength = 0;
+    // The null termination character is included in the returned log length.
+    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLength);
+    if (logLength > 0) {
+      std::unique_ptr<char[]> compileLog(new char[logLength]);
+      // The returned string is null terminated.
+      glGetShaderInfoLog(shader, logLength, NULL, compileLog.get());
+      LOG(LS_ERROR) << "Shader compile error: " << compileLog.get();
+    }
+    glDeleteShader(shader);
+    shader = 0;
+  }
+  return shader;
+}
+
+// Links a shader program with the given vertex and fragment shaders and
+// returns the program handle or 0 on error.
+GLuint RTCCreateProgram(GLuint vertexShader, GLuint fragmentShader) {
+  if (vertexShader == 0 || fragmentShader == 0) {
+    return 0;
+  }
+  GLuint program = glCreateProgram();
+  if (!program) {
+    return 0;
+  }
+  glAttachShader(program, vertexShader);
+  glAttachShader(program, fragmentShader);
+  glLinkProgram(program);
+  GLint linkStatus = GL_FALSE;
+  glGetProgramiv(program, GL_LINK_STATUS, &linkStatus);
+  if (linkStatus == GL_FALSE) {
+    glDeleteProgram(program);
+    program = 0;
+  }
+  return program;
+}
+
+// Creates and links a shader program with the given fragment shader source and
+// a plain vertex shader. Returns the program handle or 0 on error.
+GLuint RTCCreateProgramFromFragmentSource(const char fragmentShaderSource[]) {
+  GLuint vertexShader = RTCCreateShader(GL_VERTEX_SHADER, kRTCVertexShaderSource);
+  RTC_CHECK(vertexShader) << "failed to create vertex shader";
+  GLuint fragmentShader =
+      RTCCreateShader(GL_FRAGMENT_SHADER, fragmentShaderSource);
+  RTC_CHECK(fragmentShader) << "failed to create fragment shader";
+  GLuint program = RTCCreateProgram(vertexShader, fragmentShader);
+  // Shaders are created only to generate program.
+  if (vertexShader) {
+    glDeleteShader(vertexShader);
+  }
+  if (fragmentShader) {
+    glDeleteShader(fragmentShader);
+  }
+  return program;
+}
+
+// Set vertex shader variables 'position' and 'texcoord' in |program| to the
+// |gVertices| array above. It will use |vertexBuffer| and |vertexArray| to
+// store the vertex data.
+BOOL RTCSetupVerticesForProgram(GLuint program, GLuint* vertexBuffer, GLuint* vertexArray) {
+  GLint position = glGetAttribLocation(program, "position");
+  GLint texcoord = glGetAttribLocation(program, "texcoord");
+  if (position < 0 || texcoord < 0) {
+    return NO;
+  }
+#if !TARGET_OS_IPHONE
+  glGenVertexArrays(1, vertexArray);
+  if (*vertexArray == 0) {
+    return NO;
+  }
+  glBindVertexArray(*vertexArray);
+#endif
+  glGenBuffers(1, vertexBuffer);
+  if (*vertexBuffer == 0) {
+    return NO;
+  }
+  glBindBuffer(GL_ARRAY_BUFFER, *vertexBuffer);
+  glBufferData(GL_ARRAY_BUFFER, sizeof(gVertices), gVertices, GL_DYNAMIC_DRAW);
+
+  // Read position attribute from |gVertices| with size of 2 and stride of 4
+  // beginning at the start of the array. The last argument indicates offset
+  // of data within |gVertices| as supplied to the vertex buffer.
+  glVertexAttribPointer(position, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat),
+                        (void *)0);
+  glEnableVertexAttribArray(position);
+
+  // Read texcoord attribute from |gVertices| with size of 2 and stride of 4
+  // beginning at the first texcoord in the array. The last argument indicates
+  // offset of data within |gVertices| as supplied to the vertex buffer.
+  glVertexAttribPointer(texcoord, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat),
+                        (void *)(2 * sizeof(GLfloat)));
+  glEnableVertexAttribArray(texcoord);
+
+  return YES;
+}