How can I handle errors when there is no valid OpenGL context?

Question

I'm writing cross-platform (iOS, Android, OSX, Windows) library code that draws its output using OpenGL. I expect my users will often try to call my library's rendering functions without a valid OpenGL context (especially when they are first getting started), so how can I cleanly handle the error?

So far I have tried calling some OpenGL function and then calling glGetError() to see if it failed (and printing my user a helpful error message), but glGetError() segfaults if there is no context:

// Test for OpenGL Context

glClearColor(0.0f, 0.0f, 0.0f, 0.0f); // This line segfaults

if (glGetError() != GL_NO_ERROR)
    printf("You tried to call a rendering function but no OpenGL context was found!");

Is there a way to check for a valid context within OpenGL without getting a segfault?

Answer 1

You can use these vendor specific functions:

• wglGetCurrentContext() on Windows,
• aglGetCurrentContext() on OSX,
• glxGetCurrentContext() on unixoid systems with X and
• eglGetCurrentContext() on GLES based systems like iOS or Android

They all return NULL (except for eglGetCurrentContext, which returns EGL_NO_CONTEXT) if there is no valid context currently active.