OpenGL 不渲染正方形

Question

我目前是运行 opengl 4.5。

我从网上复制粘贴了一个代码来画一个三角形，效果很好。我玩了着色器，一切都很棒。

然后我有一个好主意，为什么不画一个正方形，所以我试了一下，它只渲染了背景。

这是代码：

   glfwGetFramebufferSize(window, &width, &height);
   glViewport(0, 0, width, height);


   // Build and compile our shader program
   // Vertex shader
   vertexShaderSource = read_file("res/shaders/vxShader.vert").c_str();
   fragmentShaderSource = read_file("res/shaders/fgShader.frag").c_str();


   GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
   glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
   glCompileShader(vertexShader);
   // Check for compile time errors
   GLint success;
   GLchar 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
   GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
   glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
   glCompileShader(fragmentShader);
   // Check for compile time 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
   GLuint 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);


   // Set up vertex data (and buffer(s)) and attribute pointers
   GLfloat vertices[] = {
        0.5f,  0.5f, 0.0f, // Left  
        0.0f,  0.5f, 0.0f, // Right 
        0.0f,  0.0f, 0.0f,  // Top
        0.5f,  0.0f, 0.0f  // Top  
   };
   GLuint VBO, VAO;
   glGenVertexArrays(1, &VAO);
   glGenBuffers(1, &VBO);
   // Bind the Vertex Array Object first, then bind and set vertex buffer(s) and attribute pointer(s).
   glBindVertexArray(VAO);

   glBindBuffer(GL_ARRAY_BUFFER, VBO);
   glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

   glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
   glEnableVertexAttribArray(0);

   glBindBuffer(GL_ARRAY_BUFFER, 0); // Note that this is allowed, the call to glVertexAttribPointer registered VBO as the currently bound vertex buffer object so afterwards we can safely unbind

   glBindVertexArray(0); // Unbind VAO (it's always a good thing to unbind any buffer/array to prevent strange bugs)

   // Game loop
   while (!glfwWindowShouldClose(window))
   {
       // Check if any events have been activiated (key pressed, mouse moved etc.) and call corresponding response functions
       glfwPollEvents();

       // Render
       // Clear the colorbuffer
       glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
       glClear(GL_COLOR_BUFFER_BIT);

       // Draw our first triangle
       glUseProgram(shaderProgram);
       glBindVertexArray(VAO);
       glDrawArrays(GL_POLYGON, 0, 4);
       glBindVertexArray(0);

       // Swap the screen buffers
       glfwSwapBuffers(window);
   }
   // Properly de-allocate all resources once they've outlived their purpose
   glDeleteVertexArrays(1, &VAO);
   glDeleteBuffers(1, &VBO);
   // Terminate GLFW, clearing any resources allocated by GLFW.
   glfwTerminate();
   return 0;

以防万一，我只向缓冲区添加了一个顶点，并将 glDrawArrays 参数从 GL_TRIANGLE 更改为 GL_POLYGON。我想我忘了做点什么。

Answer 1

基本类型 GL_POLYGON 已弃用，仅受兼容性配置文件 OpenGL context. If you use a core profile OpenGL context then you have to use the OpenGL primitive type GL_TRIANGLE_FAN 支持：

~~glDrawArrays(GL_POLYGON, 0, 4);~~

glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

请注意，OpenGL 只能渲染点、线和三角形。如果要渲染多边形形状，则必须 assemble 三角形。一个四边形可以由 2 个三角形组成。参见 Primitive。

OpenGL 不渲染正方形

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