OpenGL渲染管线

(也就是)OpenGL渲染一帧图形的流程

• 以下列举最简单的，渲染一个三角形的流程，你可以将它视为 精简版OpenGL渲染管线

  　　更复杂的流程也仅仅就是：在此基础上的各个流程中 添加额外的内容，而这些会在后续补充。

• * CPU将三角形的  [点坐标，及其索引信息]  传入GPU显存

• * CPU调用 gl函数编译链接挂载 shader

• * * shader是使用  类C语言： glsl 编写的程序

• * * GPU会执行shader中的内容，并根据shader程序进行绘图。

• * * GPU会   汇总shader提供的数据&CPU提供的数据，并根据他们进行绘图。

• * CPU调用 gl函数激活 GPU执行shader并绘制图

• * 以下是相关代码：

  // build and compile our shader program
  // ------------------------------------
  // vertex shader
  unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
  glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
  glCompileShader(vertexShader);
  // check for shader compile errors
  int success;
  char infoLog[512];
  glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
  if (!success)
  {
  glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
  std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
  }
  // fragment shader
  unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
  glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
  glCompileShader(fragmentShader);
  // check for shader compile errors
  glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
  if (!success)
  {
  glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
  std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
  }
  // link shaders
  unsigned int shaderProgram = glCreateProgram();
  glAttachShader(shaderProgram, vertexShader);
  glAttachShader(shaderProgram, fragmentShader);
  glLinkProgram(shaderProgram);
  // check for linking errors
  glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
  if (!success) {
  glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
  std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
  }
  glDeleteShader(vertexShader);
  glDeleteShader(fragmentShader);
  // -----------------------------以上：Shader编译，编译检查，链接，链接检查-----------------------------

// set up vertex data (and buffer(s)) and configure vertex attributes
// ------------------------------------------------------------------
//三角形顶点，及其索引信息：
　　float vertices[] = {
0.5f, 0.5f, 0.0f, // top right
0.5f, -0.5f, 0.0f, // bottom right
-0.5f, -0.5f, 0.0f, // bottom left
-0.5f, 0.5f, 0.0f // top left
};
unsigned int indices[] = { // note that we start from 0!
0, 1, 3, // first Triangle
1, 2, 3 // second Triangle
};
//向GPU传入相关数据
unsigned int VBO, VAO, EBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);

glBindBuffer(GL\_ARRAY\_BUFFER, VBO);  
glBufferData(GL\_ARRAY\_BUFFER, sizeof(vertices), vertices, GL\_STATIC\_DRAW);

glBindBuffer(GL\_ELEMENT\_ARRAY\_BUFFER, EBO);  
glBufferData(GL\_ELEMENT\_ARRAY\_BUFFER, sizeof(indices), indices, GL\_STATIC\_DRAW);  

　　 glBindVertexArray(VAOID)
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);

// note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind  
glBindBuffer(GL\_ARRAY\_BUFFER, 0); 

// remember: do NOT unbind the EBO while a VAO is active as the bound element buffer object IS stored in the VAO; keep the EBO bound.  
//glBindBuffer(GL\_ELEMENT\_ARRAY\_BUFFER, 0);

// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other  
// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.  
glBindVertexArray(0);   

　　 while (!glfwWindowShouldClose(window)) {
　　 // input
　　 // -----
　　 　　processInput(window);
　　
　　 // render
// ------
　　 　　glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
　　 　　glClear(GL_COLOR_BUFFER_BIT);
　　
　　 // draw our first triangle
　　 　　glUseProgram(shaderProgram);
　　 　　glBindVertexArray(VAO);

　　 // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
　　 　　glDrawArrays(GL_TRIANGLES, 0, 6);
　　 　　glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

　　 // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
　　 // -------------------------------------------------------------------------------
　　 　　glfwSwapBuffers(window);
　　 　　glfwPollEvents();
　　}
// optional: de-allocate all resources once they've outlived their purpose:
// ------------------------------------------------------------------------
　　glDeleteVertexArrays(1, &VAO);
　　glDeleteBuffers(1, &VBO);
　　glDeleteBuffers(1, &EBO);
　　glDeleteProgram(shaderProgram);

VAO&VBO&EBO

　　  1. VBO：一个抽象对象，OpenGL没有固定它的实现，

　　　  因此你不必了解它的实现，你只需知道VBO是  OpenGL用来管理  来自CPU数据的 一种工具：

unsigned int VBOID, VAOID, EBOID;  
//申请三个整形值，用以存放 申请的VBO,VAB,EBO的 ID    

glGenBuffers(1, &VBOID);  
glGenVertexArrays(1, &VAOID);  
glGenBuffers(1, &EBOID);  
//向OpenGL申请: 1\*VBO, 1\*VAO, 1\*EBO  并将其ID传入各自的 地址  

　 //[此地址可以是连续数组空间的首地址，也可以是单一的一个数据]

glBindVertexArray(VAOID)  
//将  
glBindBuffer(GL\_ARRAY\_BUFFER, VBOID);  
//将VBOID指向的VBO 与flag:GL\_ARRAY\_BUFFER绑定。

　　  2.