使用SDL2和OpenGL旋转相机和三角形绘制不会显示任何东西？

1 回答

• 1

  请注意， glBegin / glEnd 序列和固定功能管道矩阵堆栈的绘制几十年来已被弃用 . 阅读Fixed Function Pipeline并查看Vertex Specification和Shader以了解最先进的渲染方式 .

  如果要使用不推荐使用的绘制方式，则必须使用兼容性配置文件上下文而不是核心配置文件上下文（请参阅OpenGL Context）：

  SDL_GL_SetAttribute（SDL_GL_CONTEXT_PROFILE_MASK，SDL_GL_CONTEXT_PROFILE_CORE）;
  SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_COMPATIBILITY);

  ---

  进一步注意，glm::lookAt和[ glm::perspective ]不设置任何OpenGL状态甚至固定函数pipline矩阵 . glm - OpenGL Mathematics是一个数学库，用于执行与OpenGL相关的计算 . 两个函数都返回一个4 * 4矩阵 .

  您可以使用glLoadMatrixf将glm函数的矩阵返回加载到OpenGL固定函数管道矩阵堆栈：

  #include <glm/glm.hpp>
  #include "glm/gtc/matrix_transform.hpp"
  #include <glm/gtc/type_ptr.hpp>
  

  void Calculate()
  {
      float radius = 2.0f;
      float camX = sin(SDL_GetTicks()*0.001) * radius;
      float camZ = cos(SDL_GetTicks()*0.001) * radius;
  
      glm::mat4 perspecive_mat = glm::perspective(
          45.0f, 1.0f / 1.0f, 0.1f, 100.0f );
  
      glm::mat4 view_mat = glm::lookAt(
          glm::vec3(camX, 0.0, camZ), glm::vec3(0.0, 0.0, 0.0), glm::vec3(0.0, 1.0, 0.0) );
  
      glMatrixMode(GL_PROJECTION);
      glLoadMatrixf(glm::value_ptr(perspecive_mat));
  
      glMatrixMode(GL_MODELVIEW);
      glLoadMatrixf(glm::value_ptr(view_mat));
  }
  

  ---

  如果要使用核心配置文件，则必须创建一个简单的Shader程序：

  #include <string>
  
  std::string sh_vert = R"(
  #version 150 core
  
  in vec3 v_pos;
  in vec4 v_col;
  
  out vec4 color;
  
  uniform mat4 projection;
  uniform mat4 view;
  
  void main()
  {
      color = v_col;                    
      gl_Position = projection * view * vec4(v_pos, 1.0);
  } 
  )";
  
  std::string sh_frag = R"(
  #version 150 core
  
  in vec4 color;
  
  void main()
  {
      gl_FragColor = color;
  } 
  )";
  

  编译并链接程序：

  #include <vector>
  
  GLuint CreateShader(GLenum type, const char *code)
  {
      GLuint shaderObj = glCreateShader(type);
      glShaderSource(shaderObj, 1, &code, nullptr);
      glCompileShader(shaderObj);
  
      GLint status = GL_TRUE;
      glGetShaderiv(shaderObj, GL_COMPILE_STATUS, &status);
      if (status == GL_FALSE)
      {
          GLint logLen;
          glGetShaderiv(shaderObj, GL_INFO_LOG_LENGTH, &logLen);
          std::vector< char >log(logLen);
          GLsizei written;
          glGetShaderInfoLog(shaderObj, logLen, &written, log.data());
          std::cout << "compile error:" << std::endl << log.data() << std::endl;
      }
      return shaderObj;
  }
  
  GLuint CreateProgram()
  {
      GLuint vShObj = CreateShader(GL_VERTEX_SHADER, sh_vert.c_str());
      GLuint fShObj = CreateShader(GL_FRAGMENT_SHADER, sh_frag.c_str());
  
      GLuint progObj = glCreateProgram();
      glAttachShader(progObj, vShObj);
      glAttachShader(progObj, fShObj);
      glLinkProgram(progObj);
  
      GLint status = GL_TRUE;
      glGetProgramiv(progObj, GL_LINK_STATUS, &status);
      if (status == GL_FALSE)
      {
          GLint logLen;
          glGetProgramiv(progObj, GL_INFO_LOG_LENGTH, &logLen);
          std::vector< char >log(logLen);
          GLsizei written;
          glGetProgramInfoLog(progObj, logLen, &written, log.data());
          std::cout << "link error:" << std::endl << log.data() << std::endl;
      }
      return progObj;
  }
  

  获取属性和统一位置：

  GLuint prog;
  GLint pos_attr, col_attr, proj_loc, view_loc;
  
  void Init()
  {
      prog = CreateProgram();
      pos_attr = glGetAttribLocation(prog, "v_pos");
      col_attr = glGetAttribLocation(prog, "v_col");
      proj_loc = glGetUniformLocation(prog, "projection");
      view_loc = glGetUniformLocation(prog, "view");
  
      // ....
  
   }
  

  创建一个Vertex Array Object：

  GLuint vao;
  
  void Init()
  {
      // ....
  
      const std::vector<float> varray
      {
      // x      y     z     red   green blue
        -0.5f, -0.5f, 0.0f, 1.0f, 1.0f, 0.0f,
         0.5f,  0.0f, 0.0f, 0.0f, 1.0f, 0.0f,
         0.0f,  0.5f, 0.0f, 0.0f, 0.0f, 1.0f
      };
  
      GLuint vbo;
      glGenBuffers(1, &vbo);
      glBindBuffer(GL_ARRAY_BUFFER, vbo);
      glBufferData(GL_ARRAY_BUFFER, varray.size()*sizeof(float), varray.data(), GL_STATIC_DRAW);
  
      glGenVertexArrays(1, &vao);
      glBindVertexArray(vao);
      glVertexAttribPointer(pos_attr, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), 0);
      glEnableVertexAttribArray(pos_attr);
      glVertexAttribPointer(col_attr, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), (void*)(3*sizeof(float)));
      glEnableVertexAttribArray(col_attr);
      glBindBuffer(GL_ARRAY_BUFFER, 0);
      glBindVertexArray(0);
  }
  

  将程序对象安装为当前呈现状态的一部分并设置统一变量：

  void Calculate()
  {
      float radius = 2.0f;
      float camX = sin(SDL_GetTicks()*0.001) * radius;
      float camZ = cos(SDL_GetTicks()*0.001) * radius;
  
      glm::mat4 perspecive_mat = glm::perspective(
          45.0f, 1.0f / 1.0f, 0.1f, 100.0f );
  
      glm::mat4 view_mat = glm::lookAt(
          glm::vec3(camX, 0.0, camZ), glm::vec3(0.0, 0.0, 0.0), glm::vec3(0.0, 1.0, 0.0) );
  
      glUseProgram(prog);
      glUniformMatrix4fv(proj_loc, 1, GL_FALSE, glm::value_ptr(perspecive_mat));
      glUniformMatrix4fv(view_loc, 1, GL_FALSE, glm::value_ptr(view_mat));
  }
  

  最后绘制三角形：

  void Render()
  {
      glClearColor(0.0, 0.0, 0.0, 1.0);
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  
      glBindVertexArray(vao);
      glDrawArrays(GL_TRIANGLES, 0, 3);
      glBindVertexArray(0);
  
      SDL_GL_SwapWindow(mainWindow);
  }
  
  bool Loop()
  {
      Init();
  
      while (true) {
          // ....
  
          Calculate();
          Render();
      }
  }
  

  回复于 2024-05-20T02:25:31+08:00