學習自：https://learnopengl-cn.github.io/01%20Getting%20started/04%20Hello%20Triangle/

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OpenGL沒有直接繪制四邊形的api，所有的圖形都是通過三角形來拼接而成，一個四邊形可以通過兩個三角形拼接而成

#include <glad/glad.h>
#include?<GLFW/glfw3.h> #include <iostream>void framebuffer_size_callback(GLFWwindow* window, int width, int height); void processInput(GLFWwindow *window);// settings const unsigned int SCR_WIDTH = 800; const unsigned int SCR_HEIGHT = 600;const char *vertexShaderSource = "#version 330 core\n""layout (location = 0) in vec3 aPos;\n""void main()\n""{\n"" gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n""}\0"; const char *fragmentShaderSource = "#version 330 core\n""out vec4 FragColor;\n""void main()\n""{\n"" FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n""}\n\0";int main() {// glfw: initialize and configure// ------------------------------glfwInit();glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);#ifdef __APPLE__glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // uncomment this statement to fix compilation on OS X #endif// glfw window creation// --------------------GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);if (window == NULL){std::cout << "Failed to create GLFW window" << std::endl;glfwTerminate();return -1;}glfwMakeContextCurrent(window);glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){std::cout << "Failed to initialize GLAD" << std::endl;return -1;}// build and compile our shader program// ------------------------------------// vertex shaderint vertexShader = glCreateShader(GL_VERTEX_SHADER);glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);glCompileShader(vertexShader);// check for shader compile errorsint 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 shaderint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);glCompileShader(fragmentShader);// check for shader compile errorsglGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);if (!success){glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;}// link shadersint shaderProgram = glCreateProgram();glAttachShader(shaderProgram, vertexShader);glAttachShader(shaderProgram, fragmentShader);glLinkProgram(shaderProgram);// check for linking errorsglGetProgramiv(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 configure vertex attributes// ------------------------------------------------------------------float vertices[] = {0.5f, 0.5f, 0.0f, // top right0.5f, -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 Triangle1, 2, 3 // second Triangle};unsigned int VBO, VAO, EBO;
　　// 1. 綁定頂點數組對象glGenVertexArrays(1, &VAO);glGenBuffers(1, &VBO);glGenBuffers(1, &EBO);// 2. 把我們的頂點數組復制到一個頂點緩沖中，供OpenGL使用glBindVertexArray(VAO);glBindBuffer(GL_ARRAY_BUFFER, VBO);glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
　　 //3，復制我們的索引數組到一個索引緩沖中，供OpenGL使用
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
　　 // 4，設定頂點屬性指針glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);glEnableVertexAttribArray(0);// 解除綁定glBindBuffer(GL_ARRAY_BUFFER, 0); glBindVertexArray(0);
　　//可以通過下面這句話，來設置畫圖為線性的（第二張圖）　　
　　//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

　　//循環繪制while (!glfwWindowShouldClose(window)){// input// -----processInput(window);// render// ------glClearColor(0.2f, 0.3f, 0.3f, 1.0f);glClear(GL_COLOR_BUFFER_BIT);// draw our first triangleglUseProgram(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);// glBindVertexArray(0); // no need to unbind it every time // 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);// glfw: terminate, clearing all previously allocated GLFW resources.// ------------------------------------------------------------------glfwTerminate();return 0; }// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly // --------------------------------------------------------------------------------------------------------- void processInput(GLFWwindow *window) {if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)glfwSetWindowShouldClose(window, true); }// glfw: whenever the window size changed (by OS or user resize) this callback function executes // --------------------------------------------------------------------------------------------- void framebuffer_size_callback(GLFWwindow* window, int width, int height) {// make sure the viewport matches the new window dimensions; note that width and // height will be significantly larger than specified on retina displays.glViewport(0, 0, width, height); }

?正常情況下，我們的圖形可以繪制成下面這樣：

這樣可以看的還不是很清晰，我們可以通過調整繪圖為線性的，可以看到下面這樣：

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轉載于:https://www.cnblogs.com/icyhusky/p/10673740.html

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