Using Opengl Without X-Window System

How can I use OpenGL to render to memory without requiring any windowing system library?

Depending on the operating system you're using and the availability of drivers, you can do pure, headless, GPU accelerated OpenGL rendering using EGL. Nvidia has a nice developer blog about how to do it at https://developer.nvidia.com/blog/egl-eye-opengl-visualization-without-x-server/

The gist of it is, to create a EGL context on a display device without associating it with an output. Source (copied directly from the linked article):

#include <EGL/egl.h>
static const EGLint configAttribs[] = {
          EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
          EGL_BLUE_SIZE, 8,
          EGL_GREEN_SIZE, 8,
          EGL_RED_SIZE, 8,
          EGL_DEPTH_SIZE, 8,
          EGL_RENDERABLE_TYPE, EGL_OPENGL_BIT,
          EGL_NONE
};    

static const int pbufferWidth = …;
static const int pbufferHeight = …;

static const EGLint pbattr[] = {
        EGL_WIDTH, pbufferWidth,
        EGL_HEIGHT, pbufferHeight,
        EGL_NONE,
};

int main(int argc, char *argv[])
{
  EGLDisplay eglDpy = eglGetDisplay(EGL_DEFAULT_DISPLAY);
  EGLint major, minor;
  eglInitialize(eglDpy, &major, &minor);
  EGLint numConfigs;
  EGLConfig eglCfg;

  eglChooseConfig(eglDpy, configAttribs, &eglCfg, 1, &numConfigs);
  EGLSurface eglSurf = eglCreatePbufferSurface(eglDpy, eglCfg, pbattr);
  eglBindAPI(EGL_OPENGL_API);
  EGLContext eglCtx = eglCreateContext(eglDpy, eglCfg, EGL_NO_CONTEXT, NULL);    
  eglMakeCurrent(eglDpy, eglSurf, eglSurf, eglCtx);

  do_opengl_stuff();

  eglTerminate(eglDpy);
  return 0;
}

If you don't have access to EGL, but your OS and your GPU is supported by Linux DRM/DRI, you could go the KMS/GBM route and worth with framebuffer objects obtained through the extension mechanism (well, with Mesa you can just use them as if they were non extensions, even with OpenGL-1.x). The kmscube demo has a "surfaceless" mode, which demonstrates doing exactly that.

In short: EGL is the "clean" way do to it. KMS is the "hacky" way to do it.

Another option, probably completely outside of your scope right now, would be to use Vulkan, where strictly speaking, headless rendering is the "default", and methods for getting stuff on-screen are actual extensions to the specification:

    VK_KHR_wayland_surface
    VK_KHR_xcb_surface
    VK_KHR_xlib_surface
    VK_KHR_win32_surface

OpenGL Without GUI

Is it possible to compile a program that uses the OpenGL libraries or directly uses the GPU driver to draw to the screen?

Yes. With the EGL API this has been formalized and works most well with NVidia GPUs and their proprietary drivers. NVidia has it described on their dev blog here https://devblogs.nvidia.com/egl-eye-opengl-visualization-without-x-server/

Essentially the steps are:

Create a OpenGL context for a PBuffer

#include <EGL/egl.h>

  static const EGLint configAttribs[] = {
          EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
          EGL_BLUE_SIZE, 8,
          EGL_GREEN_SIZE, 8,
          EGL_RED_SIZE, 8,
          EGL_DEPTH_SIZE, 8,
          EGL_RENDERABLE_TYPE, EGL_OPENGL_BIT,
          EGL_NONE
  };    

  static const int pbufferWidth = 9;
  static const int pbufferHeight = 9;

  static const EGLint pbufferAttribs[] = {
        EGL_WIDTH, pbufferWidth,
        EGL_HEIGHT, pbufferHeight,
        EGL_NONE,
  };

int main(int argc, char *argv[])
{
  // 1. Initialize EGL
  EGLDisplay eglDpy = eglGetDisplay(EGL_DEFAULT_DISPLAY);

  EGLint major, minor;

  eglInitialize(eglDpy, &major, &minor);

  // 2. Select an appropriate configuration
  EGLint numConfigs;
  EGLConfig eglCfg;

  eglChooseConfig(eglDpy, configAttribs, &eglCfg, 1, &numConfigs);

  // 3. Create a surface
  EGLSurface eglSurf = eglCreatePbufferSurface(eglDpy, eglCfg, 
                                               pbufferAttribs);

  // 4. Bind the API
  eglBindAPI(EGL_OPENGL_API);

  // 5. Create a context and make it current
  EGLContext eglCtx = eglCreateContext(eglDpy, eglCfg, EGL_NO_CONTEXT, 
                                       NULL);

  eglMakeCurrent(eglDpy, eglSurf, eglSurf, eglCtx);

  // from now on use your OpenGL context

  // 6. Terminate EGL when finished
  eglTerminate(eglDpy);
  return 0;
}

and then go about the rest as per usual. Or you can even ditch the PBuffer completely and just use OpenGL manages resources, i.e. render to framebuffer objects. For that end you can omit creating the surface and just make the context current.

Here's an example for using EGL without display, no EGL surface, with OpenGL managed framebuffer.

#include <GL/glew.h>
#include <GL/glut.h>
#include <EGL/egl.h>

#include <unistd.h>
#include <stdlib.h>
#include <assert.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#include <math.h>
#include <stdio.h>

using namespace std;

namespace render
{
    int width, height;
    float aspect;

    void init();
    void display();

    int const fbo_width = 512;
    int const fbo_height = 512;

    GLuint fb, color, depth;

    void *dumpbuf;
    int dumpbuf_fd;
};

static const EGLint configAttribs[] = {
    EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
    EGL_BLUE_SIZE, 8,
    EGL_GREEN_SIZE, 8,
    EGL_RED_SIZE, 8,
    EGL_DEPTH_SIZE, 8,
    EGL_RENDERABLE_TYPE, EGL_OPENGL_BIT,
    EGL_NONE
};   

int main(int argc, char *argv[])
{
    // 1. Initialize EGL
    EGLDisplay eglDpy = eglGetDisplay(EGL_DEFAULT_DISPLAY);

    EGLint major, minor;    
    eglInitialize(eglDpy, &major, &minor);

    // 2. Select an appropriate configuration
    EGLint numConfigs;
    EGLConfig eglCfg;

    eglChooseConfig(eglDpy, configAttribs, &eglCfg, 1, &numConfigs);

    // 3. Bind the API
    eglBindAPI(EGL_OPENGL_API);

    // 3. Create a context and make it current
    EGLContext eglCtx = eglCreateContext(eglDpy, eglCfg, EGL_NO_CONTEXT, 
    NULL);

    eglMakeCurrent(eglDpy, EGL_NO_SURFACE, EGL_NO_SURFACE, eglCtx);

    glewInit();
    // from now on use your OpenGL context
    render::init();
    render::display();

    // 4. Terminate EGL when finished
    eglTerminate(eglDpy);
    return 0;
}

void CHECK_FRAMEBUFFER_STATUS()
{                                                         
    GLenum status;
    status = glCheckFramebufferStatus(GL_DRAW_FRAMEBUFFER); 
    switch(status) {
    case GL_FRAMEBUFFER_COMPLETE:
        break;

    case GL_FRAMEBUFFER_UNSUPPORTED:
    /* choose different formats */
        break;

    default:
        /* programming error; will fail on all hardware */
        throw "Framebuffer Error";
    }
}

namespace render
{
    float const light_dir[]={1,1,1,0};
    float const light_color[]={1,0.95,0.9,1};

    void init()
    {
        glGenFramebuffers(1, &fb);
        glGenTextures(1, &color);
        glGenRenderbuffers(1, &depth);

        glBindFramebuffer(GL_FRAMEBUFFER, fb);

        glBindTexture(GL_TEXTURE_2D, color);
        glTexImage2D(   GL_TEXTURE_2D, 
                0, 
                GL_RGB8, 
                fbo_width, fbo_height,
                0, 
                GL_RGBA, 
                GL_UNSIGNED_BYTE, 
                NULL);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, color, 0);

        glBindRenderbuffer(GL_RENDERBUFFER, depth);
        glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, fbo_width, fbo_height);
        glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depth);

        GLint red_bits, green_bits, blue_bits, alpha_bits;

        glGetIntegerv(GL_RED_BITS,   &red_bits);
        glGetIntegerv(GL_GREEN_BITS, &green_bits);
        glGetIntegerv(GL_BLUE_BITS,  &blue_bits);
        glGetIntegerv(GL_ALPHA_BITS, &alpha_bits);

        fprintf(stderr, "FBO format R%dG%dB%dA%d\n",
            (int)red_bits,
            (int)green_bits,
            (int)blue_bits,
            (int)alpha_bits );

        CHECK_FRAMEBUFFER_STATUS();

        dumpbuf_fd = open("/tmp/fbodump.rgb", O_CREAT|O_SYNC|O_RDWR, S_IRUSR|S_IWUSR);
        assert(-1 != dumpbuf_fd);
        dumpbuf = malloc(fbo_width*fbo_height*3);
        assert(dumpbuf);
    }

    void render()
    {
        static float a=0, b=0, c=0;

        glBindTexture(GL_TEXTURE_2D, 0);
        glEnable(GL_TEXTURE_2D);
        glBindFramebuffer(GL_FRAMEBUFFER, fb);

        glViewport(0,0,fbo_width, fbo_height);

        glClearColor(0,0,0,0);
        glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(-1, 1, -1, 1, -1, 1);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        glBegin(GL_TRIANGLES);
        glColor3f(1,0,0);
        glVertex3f(1,0,0);

        glColor3f(0,1,0);
        glVertex3f(0,1,0);

        glColor3f(0,0,1);
        glVertex3f(0,0,1);
        glEnd();

        glReadBuffer(GL_COLOR_ATTACHMENT0);
       glReadPixels(0,0,fbo_width,fbo_height,GL_RGB,GL_UNSIGNED_BYTE,dumpbuf);
        lseek(dumpbuf_fd, SEEK_SET, 0);
        write(dumpbuf_fd, dumpbuf, fbo_width*fbo_height*3);
    }
}

OpenGL without X.org in linux

Update (Sep. 17, 2017):

NVIDIA recently published an article detailing how to use OpenGL on headless systems, which is a very similar use case as the question describes.

In summary:

• Link to libOpenGL.so and libEGL.so instead of libGL.so. (Your linker options should therefore be -lOpenGL -lEGL
• Call eglGetDisplay, then eglInitialize to initialize EGL.
• Call eglChooseConfig with the config attribute EGL_SURFACE_TYPE followed with EGL_PBUFFER_BIT.
• Call eglCreatePbufferSurface, then eglBindApi(EGL_OPENGL_API);, then eglCreateContext and eglMakeCurrent.

From that point on, do your OpenGL rendering as usual, and you can blit your pixel buffer surface wherever you like. This supplementary article from NVIDIA includes a basic example and an example for multiple GPUs. The PBuffer surface can also be replaced with a window surface or pixmap surface, according to the application needs.

I regret not doing more research on this on my previous edit, but oh well. Better answers are better answers.

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Since my answer in 2010, there have been a number of major shakeups in the Linux graphics space. So, an updated answer:

Today, nouveau and the other DRI drivers have matured to the point where OpenGL software is stable and performs reasonably well in general. With the introduction of the EGL API in Mesa, it's now possible to write OpenGL and OpenGL ES applications on even Linux desktops.

You can write your application to target EGL, and it can be run without the presence of a window manager or even a compositor. To do so, you would call eglGetDisplay, eglInitialize, and ultimately eglCreateContext and eglMakeCurrent, instead of the usual glx calls to do the same.

I do not know the specific code path for working without a display server, but EGL accepts both X11 displays and Wayland displays, and I do know it is possible for EGL to operate without one. You can create GL ES 1.1, ES 2.0, ES 3.0 (if you have Mesa 9.1 or later), and OpenGL 3.1 (Mesa 9.0 or later) contexts. Mesa has not (as of Sep. 2013) yet implemented OpenGL 3.2 Core.

Notably, on the Raspberry Pi and on Android, EGL and GL ES 2.0 (1.1 on Android < 3.0) are supported by default. On the Raspberry Pi, I don't think Wayland yet works (as of Sep. 2013), but you do get EGL without a display server using the included binary drivers. Your EGL code should also be portable (with minimal modification) to iOS, if that interests you.

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Below is the outdated, previously accepted post:

I'd like to open an OpenGL context without X in linux. Is there any way at all to do it?

I believe Mesa provides a framebuffer target. If it provides any hardware acceleration at all, it will only be with hardware for which there are open source drivers that have been adapted to support such a use.

Gallium3D is also immature, and support for this isn't even on the roadmap, as far as I know.

I'd like to get a solution that works with nvidia cards.

There isn't one. Period.

NVIDIA only provides an X driver, and the Nouveau project is still immature, and doesn't support the kind of use that you're looking for, as they are currently focused only on the X11 driver.

How to use OpenGL without a window manager in Linux?

You don't have to install Gnome or KDE. These are used to managed windows, and you can launch graphical applications without having a window manager.

Therefore, you'll have to install a X server. The X server is responsible of drawing things on your screen. Without X server, you can't launch graphical applications.

Once X has been installed, launch it, export your DISPLAY environment variable, and the rest is like writing an OpenGL application which runs full screen :-)

run OpenGL program on server without window over ssh

With the current driver models, what you want to do it impossible in a way that works reliably. All the OpenGL implementations that so far exist for Linux absolutely require some kind to window (and be it an invisible, hidden 1×1 pixels small one) to create an OpenGL context.

Note that in the near future with the introduction of Wayland and a larger EGL based, OpenGL infrastructure is about to change. But we are not there yet.

Also if you can live with a slow, software implementation, Mesa has a sidekick library called "OSMesa" that gives you a OpenGL context that renders to a memory region provided by your program. But OSMesa won't use any kind of GPU acceleration.

Can you create OpenGL context without opening a window?

Yes! you can use the desktop window as the window passed to OpenGL- as long as you don't try to display anything on it ;)

Just Call GetDesktopWindow and pass the result as an argument when creating new OpenGL window.

PyOpenGL headless rendering

The solution is to use xvfb for a virtual framebuffer.

The problem is that the glfw that is installed in Ubuntu using apt-get install libglfw3 libglfw3-dev is old and unfit, so we need to compile it from source.

Here is a full working docker example:

docker run --name headless_test -ti ubuntu /bin/bash

# Inside the ubuntu shell:
apt update && apt install -y python3 python3-pip git python-opengl xvfb xorg-dev cmake
pip3 install pyopengl glfw
mkdir /projects
git clone https://github.com/glfw/glfw.git /projects/glfw
cd /projects/glfw
cmake -DBUILD_SHARED_LIBS=ON .
make
export PYGLFW_LIBRARY=/projects/glfw/src/libglfw.so
xvfb-run python3 some_script_using_pyopengl_and_glfw.py

And here is the base of PyOpenGL code to use it:

from OpenGL.GL import *
from OpenGL.GLU import *
import glfw

glfw.init()
# Set window hint NOT visible
glfw.window_hint(glfw.VISIBLE, False)
# Create a windowed mode window and its OpenGL context
window = glfw.create_window(DISPLAY_WIDTH, DISPLAY_HEIGHT, "hidden window", None, None)
# Make the window's context current
glfw.make_context_current(window)

How can I run an OpenGL application installed on a linux machine from my windows machine?

Solution

I installed two pieces of software:

PuTTY

XMing-mesa The mesa part is important.

PuTTY configuration

Connection->Seconds Between Keepalives: 30
Connection->Enable TCP Keepalives: Yes

Connection->SSH->X11->Enable X11 forwarding: Yes
Connection->SSH->X11->X display location: localhost:0:0

Lauching

Run Xming which will put simply start a process and put an icon in your system tray.
Launch putty, pointing to your linux box, with the above configuration.
Run program

Hopefully, Success!

Opengl es 2.0 without egl on desktop (windows)

EGL provides a “glue” layer between OpenGL ES 2.0 (and other Khronos graphics
APIs) and the native windowing system running on your computer, like the
X Window System common on GNU/Linux systems, Microsoft Windows, or
Mac OS X’s Quartz. Before EGL can determine what types of drawing surfaces,
or any other characteristics of the underlying system for that matter, it needs
to open a communications channel with the windowing system.
Because every windowing system has different semantics, EGL provides a
basic opaque type—the EGLDisplay—that encapsulates all of the system
dependencies for interfacing with the native windowing system. The first
operation that any application using EGL will need to do is create and initialize
a connection with the local EGL display.

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