How to create an OpenGL context on an NodeJS native addon on MacOS?

Question

Follow-up for this question.

I'm trying to create a NodeJS native addon that uses OpenGL.

I'm not able to use OpenGL functions because CGLGetCurrentContext() always returns NULL.

When trying to create a new context to draw into, CGLChoosePixelFormat always returns the error kCGLBadConnection invalid CoreGraphics connection.

What is bugging me out is that when I isolate the code that creates the OpenGL context into a standalone CPP project, it works! It just gives an error when I run it inside the NodeJS addon!

I created this NodeJS native addon project to exemplify my error: https://github.com/Psidium/node-opengl-context-error-example

This is the code that works when executed on a standalone project and errors out when running inside NodeJS:

//
//  main.cpp
//  test_cli
//
//  Created by Borges, Gabriel on 4/3/20.
//  Copyright © 2020 Psidium. All rights reserved.
//

#include <iostream>
#include <OpenGL/OpenGL.h>

int main(int argc, const char * argv[]) {
    std::cout << "Context before creating it: " << CGLGetCurrentContext() << "\n";
       CGLContextObj context;
    CGLPixelFormatAttribute attributes[2] = {
            kCGLPFAAccelerated,   // no software rendering
            (CGLPixelFormatAttribute) 0
    };
    CGLPixelFormatObj pix;
    CGLError errorCode;
    GLint num; // stores the number of possible pixel formats
    errorCode = CGLChoosePixelFormat( attributes, &pix, &num );
    if (errorCode > 0) {
      std::cout << ": Error returned by choosePixelFormat: " << errorCode << "\n";
        return 10;
    }

    errorCode = CGLCreateContext( pix, NULL, &context );
    if (errorCode > 0) {
      std::cout << ": Error returned by CGLCreateContext: " << errorCode << "\n";
      return 10 ;
    }

    CGLDestroyPixelFormat( pix );

    errorCode = CGLSetCurrentContext( context );
    if (errorCode > 0) {
      std::cout << "Error returned by CGLSetCurrentContext: " << errorCode << "\n";
      return 10;
    }
    std::cout << "Context after being created is: " << CGLGetCurrentContext() << "\n";
    return 0;
}

I already tried:

• Using fork() to create a context in a subprocess (didn't work);
• Changing the pixelformat attributes to something that will create my context (didn't work);

I have a hunch that it may have something to do with the fact that a Node native addon is a dynamically linked library, or maybe my OpenGL createContext function may not be executing on the main thread (but if this was the case, the fork() would have solved it, right?).

Answer 1

Accessing graphics hardware requires extra permissions - Windows and macOS (don't know for others) restrict creation of hardware-accelerated OpenGL context to interactive user session (I may be wrong with the terms here). From one of articles on the web:

In case the user is not logged in, the CGLChoosePixelFormat will return kCGLBadConnection

Interactive session is easier to feel than to understand; e.g. when you interactively login and launch application - it is interactive session; when process is started as service - it is non-interactive. How this is actually managed by system requires deeper reading. As far as I know, there is no easy way "escaping" non-interactive process flag.

NodeJS can be used as part of a web-server, so that I may expect that it can be exactly the problem - it is started as a service, by another non-interactive user or has other special conditions making it non-interactive. So maybe more details on how you use / start NodeJS itself might clarify why the code doesn't work. But I may expect that using OpenGL on server part might be not a good idea anyway (if this is a target); although it might be possible that software OpenGL implementation (without kCGLPFAAccelerated flag might work).

By the way, there are at least two OpenGL / WebGL extensions to NodeJS - have you tried their samples to see if they behave in the same or different way in your environment? https://github.com/google/node-gles https://github.com/mikeseven/node-webgl