OpenGL Not Seeing Triangle

Question

I can't seem to see a red Triangle.

OS: macOS on a M1 Mac // I did also do the core profile thing

Code:

#define GL_SILENCE_DEPRECATION

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include <iostream>
#include <string>

static unsigned int CompileShader(unsigned int type, const std::string& source) {
    unsigned int id = glCreateShader(type);
    const char* scr = source.c_str();
    glShaderSource(id, 1, &scr, nullptr);
    glCompileShader(id);
    
    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    
    if (result == GL_FALSE) {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char* message = (char *) alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        
        std::cout << "\nError: Failed to compile shader! Error list:\n" << message << " Type: " << (type == GL_VERTEX_SHADER ? "Vertex": "Fragment" ) << "\n";
        glDeleteShader(id);
        
        return 0;
    }
    
    return id;
}

static unsigned int CreateShader(const std::string& vertexShader, const std::string& fragmentShader) {
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);
    
    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);
    
    glDeleteShader(vs);
    glDeleteShader(fs);
    
    return program;
}

int main(void)
{
    GLFWwindow* window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;
    
    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

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent(window);
    
    // Glew init should be after valid opengl context
    if (glewInit() != GLEW_OK) {
        std::cout << "Error!\n";
    }
        
    float positions[6] = {
         0.0f,  0.5f,
        -0.5f, -0.5f,
         0.5f, -0.5f
    };
    
    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);
    
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
    
    std::string vertexShader =
    "#version 330 core\n"
    "\n"
    "layout(location = 0) in vec4 position;\n"
    "\n"
    "void main() {\n"
    "   gl_Position = position;\n"
    "}\n";
    
    std::string fragmentShader =
    "#version 330 core\n"
    "\n"
    "layout(location = 0) out vec4 color;\n"
    "\n"
    "void main() {\n"
    "   color = vec4(1.0, 1.0, 0.0, 1.0);\n"
    "}\n";
    
    unsigned int shader = CreateShader(vertexShader, fragmentShader);
    glUseProgram(shader);
    
    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);
        
        glDrawArrays(GL_TRIANGLES, 0, 3);

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

It looks like this: Image of how the window looks

Answer 1

Vertex array objects (VAOs) aren't optional in Core contexts like they are in Compatibility contexts.

You need to generate and bind a VAO before setting up your vertex attributes and drawing:

GLuint vao = 0;
glGenVertexArrays( 1, &vao );
glBindVertexArray( vao );
...
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
...
glDrawArrays( GL_TRIANGLES, 0, 3 );

All together:

#include <glad/glad.h>
#define GLFW_INCLUDE_NONE
#include <GLFW/glfw3.h>
#include <vector>
#include <iostream>

void CheckStatus( GLuint obj, bool isShader )
{
    GLint status = GL_FALSE, log[ 1 << 11 ] = { 0 };
    ( isShader ? glGetShaderiv : glGetProgramiv )( obj, isShader ? GL_COMPILE_STATUS : GL_LINK_STATUS, &status );
    if( status == GL_TRUE ) return;
    ( isShader ? glGetShaderInfoLog : glGetProgramInfoLog )( obj, sizeof( log ), NULL, (GLchar*)log );
    std::cerr << (GLchar*)log << "\n";
    std::exit( EXIT_FAILURE );
}

void AttachShader( GLuint program, GLenum type, const char* src )
{
    GLuint shader = glCreateShader( type );
    glShaderSource( shader, 1, &src, NULL );
    glCompileShader( shader );
    CheckStatus( shader, true );
    glAttachShader( program, shader );
    glDeleteShader( shader );
}

const char* const vert = R"GLSL(
#version 330 core
layout(location = 0) in vec4 position;
void main() {
    gl_Position = position;
}
)GLSL";

const char* const frag = R"GLSL(
#version 330 core
layout(location = 0) out vec4 color;
void main() {
    color = vec4(1.0, 1.0, 0.0, 1.0);
}
)GLSL";

int main( int, char** )
{
    glfwSetErrorCallback( []( int, const char* desc )
    {
        std::cerr << desc << "\n"; std::exit( EXIT_FAILURE );
    } );
    glfwInit();
    glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3 );
    glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
    glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE );
    glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE );
    GLFWwindow* window = glfwCreateWindow( 640, 480, "GLFW", NULL, NULL );
    glfwMakeContextCurrent( window );

    gladLoadGLLoader( (GLADloadproc)glfwGetProcAddress );

    float positions[6] =
    {
         0.0f,  0.5f,
        -0.5f, -0.5f,
         0.5f, -0.5f,
    };
    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);

    GLuint vao = 0;
    glGenVertexArrays( 1, &vao );
    glBindVertexArray( vao );

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);

    GLuint prog = glCreateProgram();
    AttachShader( prog, GL_VERTEX_SHADER, vert );
    AttachShader( prog, GL_FRAGMENT_SHADER, frag );
    glLinkProgram( prog );
    CheckStatus( prog, false );
    glUseProgram( prog );

    while( !glfwWindowShouldClose( window ) )
    {
        glfwPollEvents();
        int w, h;
        glfwGetFramebufferSize( window, &w, &h );
        glViewport( 0, 0, w, h );
        glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
        glDrawArrays( GL_TRIANGLES, 0, 3 );
        glfwSwapBuffers( window );
    }

    glfwTerminate();
}