Вывод квадрата шейдерами не работает

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";
 
unsigned int shaderProgram;
unsigned int VBO, VAO;

// shaders initialization
 
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
 
unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
 
shaderProgram = glCreateProgram();
 
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
 
glLinkProgram(shaderProgram);
 
glDetachShader(shaderProgram, vertexShader);
glDeleteShader(vertexShader);
 
glDetachShader(shaderProgram, fragmentShader);
glDeleteShader(fragmentShader);
 
float vertices[] =
{
    -0.5f, -0.5f, 0.0f,
     0.5f, -0.5f, 0.0f,
     0.0f,  0.5f, 0.0f
};
 
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
 
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(float), (void*)0);
glEnableVertexAttribArray(0);
 
glBindBuffer(GL_ARRAY_BUFFER, 0);
 
glBindVertexArray(0);

// drawing
 
int currentShader, currentVertexArray;
 
glGetIntegerv(GL_CURRENT_PROGRAM, &currentShader);
glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &currentVertexArray);
 
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, 3);
 
glBindVertexArray(currentVertexArray);
glUseProgram(currentShader);

// shaders initialization
 
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
 
unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
 
shaderProgram = glCreateProgram();
 
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
 
glLinkProgram(shaderProgram);
 
glDetachShader(shaderProgram, vertexShader);
glDeleteShader(vertexShader);
 
glDetachShader(shaderProgram, fragmentShader);
glDeleteShader(fragmentShader);
 
float vertices[] =
{
     0.5f,  0.5f, 0.0f,  // top right
     0.5f, -0.5f, 0.0f,  // bottom right
    -0.5f, -0.5f, 0.0f,  // bottom left
    -0.5f,  0.5f, 0.0f   // top left 
};
 
// note that we start from 0
unsigned int indices[] =
{
    0, 1, 3,  // first Triangle
    1, 2, 3   // second Triangle
};
 
glGenVertexArrays(1, &VAO);
 
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
 
glBindVertexArray(VAO);
 
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
 
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
 
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
 
glBindBuffer(GL_ARRAY_BUFFER, 0);
 
glBindVertexArray(0);

// drawing
 
int currentShader, currentVertexArray;
 
glGetIntegerv(GL_CURRENT_PROGRAM, &currentShader);
glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &currentVertexArray);
 
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
 
glBindVertexArray(currentVertexArray);
glUseProgram(currentShader);

glEnable(GL_CULL_FACE);
glCullFace(GL_BACK);

unsigned int indices[] =
{
 3, 1, 0, // first Triangle
 3, 2, 1 // second Triangle
};