编写OpenGL和OpenGL ES兼容代码的指南？

#include <glad/glad.h>
#include <GLES2/gl2.h>

int main() {
    // 初始化GLAD
    if (!gladLoadGLLoader((GLADloadproc)glGetString(GL_GL_LOADER))) {
        return -1;
    }

    // 创建并初始化着色器
    GLuint shaderProgram = glCreateProgram();
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);

    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);

    glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    glCompileShader(fragmentShader);

    // 链接着色器
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);

    // 激活该着色器
    glUseProgram(shaderProgram);

    // 创建并初始化顶点数据
    GLfloat vertices[] = {
        -0.5f, -0.5f, 0.0f,
        -0.5f, 0.5f, 0.0f,
        0.5f, 0.5f, 0.0f};

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // 定义顶点属性
    GLint posAttrib = glGetAttribLocation(shaderProgram, "a_position");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), 0);

    GLint texCoordAttrib = glGetAttribLocation(shaderProgram, "a_texCoord");
    glEnableVertexAttribArray(texCoordAttrib);
    glVertexAttribPointer(texCoordAttrib, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), (void*)(2 * sizeof(GLfloat)));

    // 解绑
    glBindTexture(GL_TEXTURE_2D, 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    // 渲染
    glViewport(0, 0, width, height);
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

    return 0;
}

// 初始化GLAD

if (!gladLoadGLES2Loader((GLADloadproc)glGetString(GL_GL_LOADER))) {

    return -1;

}

// 创建并初始化着色器

GLuint shaderProgram = glCreateProgram();

GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);

GLuint fragmentShader