OpenGL Not Drawing To SDL2 Window - c++

Question

So I am working on making a game in c++ and I am using SDL2 and OpenGL/GLEW. I am attempting to just draw basic shapes to my window, however, it is just creating a black screen when it should be drawing a triangle. This is the code.
Game Loop:
int main(int argc, char** argv) {
Window window("Test", 600, 400);
RenderingEngine e(window);
e.Init();
while (!window.IsCloseRequested()) {
window.SwapBuffers();
e.Render();
}
return 0;
}
Window Class:
Window::Window(const std::string& title, unsigned int width, unsigned int height) :
m_title(title), m_width(width), m_height(height), m_isCloseRequested(false) {
SDL_Init(SDL_INIT_VIDEO);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
m_window = SDL_CreateWindow(title.c_str(), SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
width, height, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
m_glContext = SDL_GL_CreateContext(m_window);
SDL_GL_MakeCurrent(m_window, m_glContext);
SDL_GL_SetSwapInterval(1);
glewExperimental = GL_TRUE;
GLenum res = glewInit();
if (res != GLEW_OK) {
std::cerr << "Error initializting OpenGL." << std::endl;
exit(1);
}
}
void Window::SwapBuffers() {
SDL_GL_SwapWindow(m_window);
}
RenderingEngine Class:
RenderingEngine::RenderingEngine(const Window& window) : m_window(&window) {
}
RenderingEngine::~RenderingEngine() {
if (m_window) delete m_window;
}
void RenderingEngine::Init() {
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glFrontFace(GL_CW);
glCullFace(GL_BACK);
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
glEnable(GL_FRAMEBUFFER_SRGB);
}
void RenderingEngine::Render() {
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(1.0f, 1.0f, 1.0f);
glBegin(GL_TRIANGLES);
glVertex3f(-1.0f, -1.0f, 0.0f);
glVertex3f(1.0f, -1.0f, 0.0f);
glVertex3f(0.0f, 1.0f, 0.0f);
glEnd();
}
I cannot figure out why it isn't drawing to the screen, so any help is greatly appreciated. Thanks!

Answer 1

You're setting up back face culling specifying that your front facing triangles have clockwise winding order, and you want to cull everything that is not front facing:
glFrontFace(GL_CW);
glCullFace(GL_BACK);
glEnable(GL_CULL_FACE);
But the triangle you specify has counter-clockwise winding order:
glVertex3f(-1.0f, -1.0f, 0.0f);
glVertex3f(1.0f, -1.0f, 0.0f);
glVertex3f(0.0f, 1.0f, 0.0f);
You can verify that by drawing the points on a piece of paper, with the x-axis going right and the y-axis up. You will see the order of points is counter-clockwise around the origin.
Based on this, your triangle is eliminated by back face culling. Since using counter-clockwise winding order is much more commonly used with OpenGL, I would suggest using it by changing the glFrontFace() call to:
glFrontFace(GL_CCW);
Or don't make the call at all, since this is the default.

Answer 2

you didn`t loaded View/Projection/Model matrices ... i guess that would be a problem... also you should use shaders if you want to make in 3.2 style