GLSL Simple example shows blanks screen on OSX - c++

Question

I'm trying to make a simple program to work. I am using SD2 + OpenGL Shading Language. Also, I'm trying to this on MacOS, more precisely 10.15.5.
I know Apple is deprecating OpenGL in favor of Metal, but it seems they are still supporting at least up to OpenGL 4.1.
This is a simplified version of the program I'm trying to run:
#include <OpenGL/glext.h>
#include <OpenGL/glu.h>
#include <SDL.h>
#include <iostream>
const int WIDTH = 600;
const int HEIGHT = 600;
const int numVAOs = 1;
GLuint renderingProgram;
GLuint vao[numVAOs];
GLuint createShaderProgram() {
GLint vertCompiled;
GLint fragCompiled;
GLint linked;
const char *vshaderSource =
"#version 410\n"
"void main(void)\n"
"{gl_Position = vec4(0.0, 0.0, 0.0, 1.0); }";
const char *fshaderSource =
"#version 410\n"
"out vec4 color; \n"
"void main(void)\n"
"{color = vec4(1.0, 0.0, 0.0, 1.0);}";
GLuint vShader = glCreateShader(GL_VERTEX_SHADER);
GLuint fShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(vShader, 1, &vshaderSource, NULL);
glShaderSource(fShader, 1, &fshaderSource, NULL);
glCompileShader(vShader);
glCompileShader(fShader);
GLuint vfProgram = glCreateProgram();
glAttachShader(vfProgram, vShader);
glAttachShader(vfProgram, fShader);
glLinkProgram(vfProgram);
return vfProgram;
}
int main() {
SDL_Window *window;
SDL_GLContext gl_context;
if (SDL_Init(SDL_INIT_VIDEO) != 0) {
return -1;
}
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
window = SDL_CreateWindow(
"OpenGL Shaders",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
WIDTH,
HEIGHT,
SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
gl_context = SDL_GL_CreateContext(window);
std::cout << glGetString(GL_VERSION) << std::endl;
renderingProgram = createShaderProgram();
glGenVertexArraysAPPLE(numVAOs, vao);
glBindVertexArrayAPPLE(vao[0]);
bool isRunning = true;
SDL_Event event;
while (isRunning) {
while (SDL_PollEvent(&event)) {
switch (event.type) {
case SDL_QUIT:
isRunning = false;
break;
}
}
glClearColor(1.0, 1.0, 1.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(renderingProgram);
glPointSize(30.0f);
glDrawArrays(GL_POINTS, 0, 1);
SDL_GL_SwapWindow(window);
}
SDL_GL_DeleteContext(gl_context);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
This shows only a blank screen and on the console it prints 4.1 ATI-3.9.15. So I am sure I got the correct profile.
I have tried playing with the headers. It seems i don't need a library to get extension names, seems Apple already has them int heir OpenGL headers.
The full program has some routines which handles errors when creating/linking the shaders and I can tell they are not failing to compile/link.
The program should show a point in the middle of the screen, but is not showing anything but a white screen(the clear color).
Any idea what am I missing or doing wrong?

Answer 1

Ok. I made it work.
The problem was this lines:
glGenVertexArraysAPPLE(numVAOs, vao);
glBindVertexArrayAPPLE(vao[0]);
For some reason, the APPLE version of those doesn't work.
What I did is:
Install GLEW with brew (which I thought I didn't need)
Update my cmake file to link glew correctly
Add glew headers and glew_init()
Replace the APPLE functions with "normal" ones.
glGenVertexArrays(numVAOs, vao);
glBindVertexArray(vao[0]);
Now the program shows points/triangles
Hope this helps anyone else in the future.