Create openGL context in linux console(Raspbian)

Question

I want to make a minimal visual display in console with openGL, but as far as my knowledge goes there has to be a window system involved(glut, glfw, sdl, etc..).

I've seen omxplayer build a graphic environment(I just assume it is openGL or something similar, so please correct me if I'm wrong) from console, in order to save some processing power, and make movies watchable in the PI.

I'm just wondering how do they do it? Is there some literature in the topic? I'm mostly interested in solutions in C/C++, but any language with these capabilities would be great to know about!

I scavenged through the source code, but couldn't really find a clue about this particular task. Any help or pointer would be appreciated!

Answer 1

Note: the Raspberry Pi does OpenGL ES, not OpenGL.

You can find examples of making console based OpenGL ES applications in the VideoCore SDK:

/opt/vc/src/hello_pi

I'm not sure what you mean by "window system", especially as you mention SDL. You can absolutely use SDL + OpenGL ES in the console. That's what the Quake3 port (and the Quake2 port I made) uses.

Answer 2

It uses the EGL native platform interface.

Here's some code from the SubtitleRenderer class:

void SubtitleRenderer::initialize_vg() {
  // get an EGL display connection
  display_ = eglGetDisplay(EGL_DEFAULT_DISPLAY);
  ENFORCE(display_);

  // initialize the EGL display connection
  ENFORCE(eglInitialize(display_, NULL, NULL));

  // get an appropriate EGL frame buffer configuration
  static const EGLint attribute_list[] = {
    EGL_RED_SIZE, 8,
    EGL_GREEN_SIZE, 8,
    EGL_BLUE_SIZE, 8,
    EGL_ALPHA_SIZE, 8,
    EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
    EGL_NONE
  };
  EGLConfig config{};
  EGLint num_config{};

  ENFORCE(eglChooseConfig(display_, attribute_list, &config, 1, &num_config));