opengl 三角形

最后效果：

OpenGL version: 4.1 Metal
不知道为啥必须使用VAO 才行。

#include <glad/glad.h>
#include <GLFW/glfw3.h>

#include <iostream>
#include <vector>

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 = R"(
    #version 100
    attribute vec2 a_position;
    void main() {
        gl_Position = vec4(a_position, 0.0, 1.0);
    }
)";

const char *fragmentShaderSource = R"(
    #version 100
    precision mediump float;
    void main() {
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);  // Red color
    }
)";

GLuint compileShader(GLenum type, const char *source)
{
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &source, nullptr);
    glCompileShader(shader);

    GLint compiled;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
    if (!compiled)
    {
        GLint infoLen;
        glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);
        std::vector<char> infoLog(infoLen);
        glGetShaderInfoLog(shader, infoLen, nullptr, infoLog.data());
        std::cerr << "Error compiling shader: " << infoLog.data() << std::endl;
        glDeleteShader(shader);
        return 0;
    }

    return shader;
}

GLuint createProgram(const char *vertexSource, const char *fragmentSource)
{
    GLuint vertexShader = compileShader(GL_VERTEX_SHADER, vertexSource);
    GLuint fragmentShader = compileShader(GL_FRAGMENT_SHADER, fragmentSource);

    GLuint program = glCreateProgram();
    glAttachShader(program, vertexShader);
    glAttachShader(program, fragmentShader);
    glLinkProgram(program);

    GLint linked;
    glGetProgramiv(program, GL_LINK_STATUS, &linked);
    if (!linked)
    {
        GLint infoLen;
        glGetProgramiv(program, GL_INFO_LOG_LENGTH, &infoLen);
        std::vector<char> infoLog(infoLen);
        glGetProgramInfoLog(program, infoLen, nullptr, infoLog.data());
        std::cerr << "Error linking program: " << infoLog.data() << std::endl;
        glDeleteProgram(program);
        return 0;
    }

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    return program;
}

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);
#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;
    }

    glViewport(0, 0, SCR_WIDTH, SCR_HEIGHT);

    GLuint program = createProgram(vertexShaderSource, fragmentShaderSource);
    glUseProgram(program);

    if (glGetError() != GL_NO_ERROR)
    {
        std::cerr << "Error in glUseProgram." << std::endl;
    }

    // Define vertex data
    GLfloat vertices[] = {
        0.0f, 0.5f,   // Vertex 1
        -0.5f, -0.5f, // Vertex 2
        0.5f, -0.5f   // Vertex 3
    };

    // 创建 VAO 并绑定
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    // Create and bind vertex buffer (VBO)
    GLuint vbo;
    glGenBuffers(1, &vbo);
    GLenum error = glGetError();
    if (error != GL_NO_ERROR)
    {
        std::cerr << "Error during drawing 1: " << error << std::endl;
    }

    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    error = glGetError();
    if (error != GL_NO_ERROR)
    {
        std::cerr << "Error during drawing 2: " << error << std::endl;
    }

    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    error = glGetError();
    if (error != GL_NO_ERROR)
    {
        std::cerr << "Error during drawing 3: " << error << std::endl;
    }

    // Get the location of the attribute
    GLint aPositionLocation = glGetAttribLocation(program, "a_position");
    if (aPositionLocation == -1)
    {
        std::cerr << "Error: Attribute 'a_position' not found in shader." << std::endl;
        return -1;
    }

    glVertexAttribPointer(aPositionLocation, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), (GLvoid *)0);
    glEnableVertexAttribArray(aPositionLocation);

    GLenum err = glGetError();
    if (err != GL_NO_ERROR)
    {
        std::cerr << "OpenGL error: " << err << std::endl;
    }

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

    // Get OpenGL version
    const char *version = (const char *)glGetString(GL_VERSION);
    std::cout << "OpenGL version: " << version << std::endl;

    while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);

        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        GLenum drawError = glGetError();

        glBindVertexArray(vao);

        glUseProgram(program);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // Cleanup
    glDeleteBuffers(1, &vbo);
    glfwTerminate();
    return 0;
}

void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

void framebuffer_size_callback(GLFWwindow *window, int width, int height)
{
    glViewport(0, 0, width, height);
}