setting up and using modern OpenGL 4.5 core context on X11 with EGL

x11_opengl.c

// example how to set up OpenGL core context on X11 with EGL
// and use basic functionality of OpenGL 4.5 version

// to compile on Ubuntu first install following packages: build-essential libx11-dev libgl-dev libegl-dev
// then run:
// gcc x11_opengl.c -o x11_opengl -lm -lX11 -lEGL

// important extension functionality used here:
// (4.3) KHR_debug:                     https://www.khronos.org/registry/OpenGL/extensions/KHR/KHR_debug.txt
// (4.5) ARB_direct_state_access:       https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_direct_state_access.txt
// (4.1) ARB_separate_shader_objects:   https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_separate_shader_objects.txt
// (4.2) ARB_shading_language_420pack:  https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_shading_language_420pack.txt
// (4.3) ARB_explicit_uniform_location: https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_explicit_uniform_location.txt

// assumes following EGL extensions are present (should be always present on modern EGL 1.5 implementation):
// EGL_KHR_surfaceless_context: https://registry.khronos.org/EGL/extensions/KHR/EGL_KHR_surfaceless_context.txt
// EGL_KHR_no_config_context:   https://registry.khronos.org/EGL/extensions/KHR/EGL_KHR_no_config_context.txt
// EGL_KHR_platform_x11:        https://registry.khronos.org/EGL/extensions/KHR/EGL_KHR_platform_x11.txt

#include <X11/Xlib.h>
#include <EGL/egl.h>
#include <EGL/eglext.h>
#include <GL/glcorearb.h>

#include <time.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

// replace this with your favorite Assert() implementation
#include <assert.h>
#define Assert(cond) assert(cond)

// make sure you use functions that are valid for selected GL version (specified when context is created)
#define GL_FUNCTIONS(X) \
    X(PFNGLENABLEPROC,                   glEnable                   ) \
    X(PFNGLDISABLEPROC,                  glDisable                  ) \
    X(PFNGLBLENDFUNCPROC,                glBlendFunc                ) \
    X(PFNGLVIEWPORTPROC,                 glViewport                 ) \
    X(PFNGLCLEARCOLORPROC,               glClearColor               ) \
    X(PFNGLCLEARPROC,                    glClear                    ) \
    X(PFNGLDRAWBUFFERPROC,               glDrawBuffer               ) \
    X(PFNGLDRAWARRAYSPROC,               glDrawArrays               ) \
    X(PFNGLCREATEBUFFERSPROC,            glCreateBuffers            ) \
    X(PFNGLNAMEDBUFFERSTORAGEPROC,       glNamedBufferStorage       ) \
    X(PFNGLBINDVERTEXARRAYPROC,          glBindVertexArray          ) \
    X(PFNGLCREATEVERTEXARRAYSPROC,       glCreateVertexArrays       ) \
    X(PFNGLVERTEXARRAYATTRIBBINDINGPROC, glVertexArrayAttribBinding ) \
    X(PFNGLVERTEXARRAYVERTEXBUFFERPROC,  glVertexArrayVertexBuffer  ) \
    X(PFNGLVERTEXARRAYATTRIBFORMATPROC,  glVertexArrayAttribFormat  ) \
    X(PFNGLENABLEVERTEXARRAYATTRIBPROC,  glEnableVertexArrayAttrib  ) \
    X(PFNGLCREATESHADERPROGRAMVPROC,     glCreateShaderProgramv     ) \
    X(PFNGLGETPROGRAMIVPROC,             glGetProgramiv             ) \
    X(PFNGLGETPROGRAMINFOLOGPROC,        glGetProgramInfoLog        ) \
    X(PFNGLGENPROGRAMPIPELINESPROC,      glGenProgramPipelines      ) \
    X(PFNGLUSEPROGRAMSTAGESPROC,         glUseProgramStages         ) \
    X(PFNGLBINDPROGRAMPIPELINEPROC,      glBindProgramPipeline      ) \
    X(PFNGLPROGRAMUNIFORMMATRIX2FVPROC,  glProgramUniformMatrix2fv  ) \
    X(PFNGLBINDTEXTUREUNITPROC,          glBindTextureUnit          ) \
    X(PFNGLCREATETEXTURESPROC,           glCreateTextures           ) \
    X(PFNGLTEXTUREPARAMETERIPROC,        glTextureParameteri        ) \
    X(PFNGLTEXTURESTORAGE2DPROC,         glTextureStorage2D         ) \
    X(PFNGLTEXTURESUBIMAGE2DPROC,        glTextureSubImage2D        ) \
    X(PFNGLDEBUGMESSAGECALLBACKPROC,     glDebugMessageCallback     )

#define X(type, name) static type name;
GL_FUNCTIONS(X)
#undef X

#define STR2(x) #x
#define STR(x) STR2(x)

static void FatalError(const char* message)
{
    fprintf(stderr, "%s\n", message);

    char cmd[1024];
    snprintf(cmd, sizeof(cmd), "zenity --error --no-wrap --text=\"%s\"", message);
    system(cmd);

    exit(0);
}

#ifndef NDEBUG
static void APIENTRY DebugCallback(
    GLenum source, GLenum type, GLuint id, GLenum severity,
    GLsizei length, const GLchar* message, const void* user)
{
    fprintf(stderr, "%s\n", message);
    if (severity == GL_DEBUG_SEVERITY_HIGH || severity == GL_DEBUG_SEVERITY_MEDIUM)
    {
        assert(!"OpenGL API usage error! Use debugger to examine call stack!");
    }
}
#endif

int main()
{
    Display* dpy = XOpenDisplay(NULL);
    if (!dpy)
    {
        FatalError("Cannot open X display");
    }

    // first create EGL context that can be done independently from any X11 windows created later

    // initialize EGL
    EGLDisplay* display;
    {
        display = eglGetPlatformDisplay(EGL_PLATFORM_X11_KHR, dpy, NULL);
        if (display == EGL_NO_DISPLAY)
        {
            FatalError("Cannot create EGL display");
        }

        EGLint major, minor;
        if (!eglInitialize(display, &major, &minor))
        {
            FatalError("Cannot initialize EGL display");
        }
        if (major < 1 || (major == 1 && minor < 5))
        {
            FatalError("EGL version 1.5 or higher required");
        }
    }

    // choose OpenGL API for EGL, by default it uses OpenGL ES
    EGLBoolean ok = eglBindAPI(EGL_OPENGL_API);
    Assert(ok && "Failed to select OpenGL API for EGL");

    // first create EGL context, suface doesn't matter, this context can be shared across many surfaces
    EGLContext* context;
    {
        EGLint attr[] =
        {
            EGL_CONTEXT_MAJOR_VERSION, 4,
            EGL_CONTEXT_MINOR_VERSION, 5,
            EGL_CONTEXT_OPENGL_PROFILE_MASK, EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT,
#ifndef NDEBUG
            // ask for debug context for non "Release" builds
            // this is so we can enable debug callback
            EGL_CONTEXT_OPENGL_DEBUG, EGL_TRUE,
#endif
            EGL_NONE,
        };

        context = eglCreateContext(display, EGL_NO_CONFIG_KHR, EGL_NO_CONTEXT, attr);
        if (context == EGL_NO_CONTEXT)
        {
            FatalError("Cannot create EGL context, OpenGL 4.5 not supported?");
        }
    }

    // make GL context active on current thread, no output surface needed
    // you can skip this and activate GL context only when you have EGL surface created
    // if all you want is to have only one context & one surface
    ok = eglMakeCurrent(display, EGL_NO_SURFACE, EGL_NO_SURFACE, context);
    Assert(ok && "Failed to make context current");

    // load OpenGL functions
#define X(type, name) name = (type)eglGetProcAddress(#name); Assert(name);
    GL_FUNCTIONS(X)
#undef X

#ifndef NDEBUG
    // enable debug callback
    glDebugMessageCallback(&DebugCallback, NULL);
    glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS);
#endif

    // now can create arbitrary amount of X11 windows & their EGL surface
    // this example creates only one window

    XSetWindowAttributes attributes =
    {
        .event_mask = StructureNotifyMask,
    };

    // create window
    int width = 1280;
    int height = 720;
    Window window = XCreateWindow(
        dpy, DefaultRootWindow(dpy),
        0, 0, width, height,
        0, CopyFromParent, InputOutput, CopyFromParent, CWEventMask,
        &attributes);
    Assert(window && "Failed to create window");

    // uncomment in case you want fixed size window
    //XSizeHints* hints = XAllocSizeHints();
    //Assert(hints);
    //hints->flags |= PMinSize | PMaxSize;
    //hints->min_width  = hints->max_width  = width;
    //hints->min_height = hints->max_height = height;
    //XSetWMNormalHints(dpy, window, hints);
    //XFree(hints);

    // set window title
    XStoreName(dpy, window, "OpenGL Window");

    // subscribe to window close notification
    Atom WM_PROTOCOLS = XInternAtom(dpy, "WM_PROTOCOLS", False);
    Atom WM_DELETE_WINDOW = XInternAtom(dpy , "WM_DELETE_WINDOW", False);
    XSetWMProtocols(dpy, window, &WM_DELETE_WINDOW, 1);

    // create EGL surface for X11 window
    EGLSurface* surface = EGL_NO_SURFACE;
    {
        // first query matching EGL configurations
        EGLConfig configs[64];
        EGLint config_count = sizeof(configs)/sizeof(configs[0]);
        {
            EGLint attr[] =
            {
                EGL_SURFACE_TYPE,      EGL_WINDOW_BIT,
                EGL_CONFORMANT,        EGL_OPENGL_BIT,
                EGL_RENDERABLE_TYPE,   EGL_OPENGL_BIT,
                EGL_COLOR_BUFFER_TYPE, EGL_RGB_BUFFER,

                EGL_RED_SIZE,      8,
                EGL_GREEN_SIZE,    8,
                EGL_BLUE_SIZE,     8,
                EGL_DEPTH_SIZE,   24,
                EGL_STENCIL_SIZE,  8,

                // uncomment for multisampled framebuffer
                //EGL_SAMPLE_BUFFERS, 1,
                //EGL_SAMPLES,        4, // 4x MSAA

                EGL_NONE,
            };
            if (!eglChooseConfig(display, attr, configs, config_count, &config_count) || config_count == 0)
            {
                FatalError("Cannot choose EGL configs");
            }
        }

        // then try all configs, to find out which one works for selected attributes, because
        // it is not guaranteed that first config will work - as there's no way to choose config
        // with specific EGL_GL_COLORSPACE value
        for (EGLint i=0; i<config_count; i++)
        {
            EGLAttrib attr[] =
            {
                EGL_RENDER_BUFFER, EGL_BACK_BUFFER, // double buffered framebuffer

                // uncomment for sRGB framebuffer
                // don't forget to call glEnable(GL_FRAMEBUFFER_SRGB) if shader outputs linear
                //EGL_GL_COLORSPACE, EGL_GL_COLORSPACE_SRGB,

                EGL_NONE,
            };
            surface = eglCreatePlatformWindowSurface(display, configs[i], &window, attr);
            if (surface != EGL_NO_SURFACE)
            {
                break;
            }
        }

        if (surface == EGL_NO_SURFACE)
        {
            FatalError("Cannot create EGL surface");
        }
    }

    // create GL objects

    struct Vertex
    {
        float position[2];
        float uv[2];
        float color[3];
    };

    // vertex buffer containing triangle vertices
    GLuint vbo;
    {
        struct Vertex data[] =
        {
            { { -0.00f, +0.75f }, { 25.0f, 50.0f }, { 1, 0, 0 } },
            { { +0.75f, -0.50f }, {  0.0f,  0.0f }, { 0, 1, 0 } },
            { { -0.75f, -0.50f }, { 50.0f,  0.0f }, { 0, 0, 1 } },
        };
        glCreateBuffers(1, &vbo);
        glNamedBufferStorage(vbo, sizeof(data), data, 0);
    }

    // vertex input
    GLuint vao;
    {
        glCreateVertexArrays(1, &vao);

        GLint vbuf_index = 0;
        glVertexArrayVertexBuffer(vao, vbuf_index, vbo, 0, sizeof(struct Vertex));

        GLint a_pos = 0;
        glVertexArrayAttribFormat(vao, a_pos, 2, GL_FLOAT, GL_FALSE, offsetof(struct Vertex, position));
        glVertexArrayAttribBinding(vao, a_pos, vbuf_index);
        glEnableVertexArrayAttrib(vao, a_pos);

        GLint a_uv = 1;
        glVertexArrayAttribFormat(vao, a_uv, 2, GL_FLOAT, GL_FALSE, offsetof(struct Vertex, uv));
        glVertexArrayAttribBinding(vao, a_uv, vbuf_index);
        glEnableVertexArrayAttrib(vao, a_uv);

        GLint a_color = 2;
        glVertexArrayAttribFormat(vao, a_color, 3, GL_FLOAT, GL_FALSE, offsetof(struct Vertex, color));
        glVertexArrayAttribBinding(vao, a_color, vbuf_index);
        glEnableVertexArrayAttrib(vao, a_color);
    }

    // checkerboard texture, with 50% transparency on black colors
    GLuint texture;
    {
        unsigned int pixels[] =
        {
            0x80000000, 0xffffffff,
            0xffffffff, 0x80000000,
        };

        glCreateTextures(GL_TEXTURE_2D, 1, &texture);
        glTextureParameteri(texture, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTextureParameteri(texture, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTextureParameteri(texture, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTextureParameteri(texture, GL_TEXTURE_WRAP_T, GL_REPEAT);

        GLsizei width = 2;
        GLsizei height = 2;
        glTextureStorage2D(texture, 1, GL_RGBA8, width, height);
        glTextureSubImage2D(texture, 0, 0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
    }

    // fragment & vertex shaders for drawing triangle
    GLuint pipeline, vshader, fshader;
    {
        const char* glsl_vshader =
            "#version 450 core                             \n"
            "#line " STR(__LINE__) "                     \n\n" // actual line number in this file for nicer error messages
            "                                              \n"
            "layout (location=0) in vec2 a_pos;            \n" // position attribute index 0
            "layout (location=1) in vec2 a_uv;             \n" // uv attribute index 1
            "layout (location=2) in vec3 a_color;          \n" // color attribute index 2
            "                                              \n"
            "layout (location=0)                           \n" // (from ARB_explicit_uniform_location)
            "uniform mat2 u_matrix;                        \n" // matrix uniform location 0
            "                                              \n"
            "out gl_PerVertex { vec4 gl_Position; };       \n" // required because of ARB_separate_shader_objects
            "out vec2 uv;                                  \n"
            "out vec4 color;                               \n"
            "                                              \n"
            "void main()                                   \n"
            "{                                             \n"
            "    vec2 pos = u_matrix * a_pos;              \n"
            "    gl_Position = vec4(pos, 0, 1);            \n"
            "    uv = a_uv;                                \n"
            "    color = vec4(a_color, 1);                 \n"
            "}                                             \n"
        ;

        const char* glsl_fshader =
            "#version 450 core                             \n"
            "#line " STR(__LINE__) "                     \n\n" // actual line number in this file for nicer error messages
            "                                              \n"
            "in vec2 uv;                                   \n"
            "in vec4 color;                                \n"
            "                                              \n"
            "layout (binding=0)                            \n" // (from ARB_shading_language_420pack)
            "uniform sampler2D s_texture;                  \n" // texture unit binding 0
            "                                              \n"
            "layout (location=0)                           \n"
            "out vec4 o_color;                             \n" // output fragment data location 0
            "                                              \n"
            "void main()                                   \n"
            "{                                             \n"
            "    o_color = color * texture(s_texture, uv); \n"
            "}                                             \n"
        ;

        vshader = glCreateShaderProgramv(GL_VERTEX_SHADER, 1, &glsl_vshader);
        fshader = glCreateShaderProgramv(GL_FRAGMENT_SHADER, 1, &glsl_fshader);

        GLint linked;
        glGetProgramiv(vshader, GL_LINK_STATUS, &linked);
        if (!linked)
        {
            char message[1024];
            glGetProgramInfoLog(vshader, sizeof(message), NULL, message);
            fprintf(stderr, "%s\n", message);
            Assert(!"Failed to create vertex shader!");
        }

        glGetProgramiv(fshader, GL_LINK_STATUS, &linked);
        if (!linked)
        {
            char message[1024];
            glGetProgramInfoLog(fshader, sizeof(message), NULL, message);
            fprintf(stderr, "%s\n", message);
            Assert(!"Failed to create fragment shader!");
        }

        glGenProgramPipelines(1, &pipeline);
        glUseProgramStages(pipeline, GL_VERTEX_SHADER_BIT, vshader);
        glUseProgramStages(pipeline, GL_FRAGMENT_SHADER_BIT, fshader);
    }

    // setup global GL state
    {
        // enable alpha blending
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

        // disble depth testing
        glDisable(GL_DEPTH_TEST);

        // disable culling
        glDisable(GL_CULL_FACE);
    }

    // show the window
    XMapWindow(dpy, window);

    // activate EGL context for specific EGL surface on current thread
    // do this call before issuing draw calls to make the output go to specific EGL surface
    ok = eglMakeCurrent(display, surface, surface, context);
    Assert(ok && "Failed to make context current");

    // use 0 to disable vsync
    int vsync = 1;
    ok = eglSwapInterval(display, vsync);
    Assert(ok && "Failed to set vsync");

    struct timespec c1;
    clock_gettime(CLOCK_MONOTONIC, &c1);

    float angle = 0;

    for (;;)
    {
        // process all incoming X11 events
        if (XPending(dpy))
        {
            XEvent event;
            XNextEvent(dpy, &event);
            if (event.type == ClientMessage)
            {
                if (event.xclient.message_type == WM_PROTOCOLS)
                {
                    Atom protocol = event.xclient.data.l[0];
                    if (protocol == WM_DELETE_WINDOW)
                    {
                        // window closed, exit the for loop
                        break;
                    }
                 }
            }
            continue;
        }

        // get current window size
        XWindowAttributes attr;
        Status status = XGetWindowAttributes(dpy, window, &attr);
        Assert(status && "Failed to get window attributes");

        width = attr.width;
        height = attr.height;

        struct timespec c2;
        clock_gettime(CLOCK_MONOTONIC, &c2);
        float delta = (float)(c2.tv_sec - c1.tv_sec) + 1e-9f * (c2.tv_nsec - c1.tv_nsec);
        c1 = c2;

        // render only if window size is non-zero
        if (width != 0 && height != 0)
        {
            // make sure backbuffer is selected for output
            glDrawBuffer(GL_BACK);

            // setup output size covering all client area of window
            glViewport(0, 0, width, height);

            // clear screen
            glClearColor(0.392f, 0.584f, 0.929f, 1.f);
            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

            // setup rotation matrix in uniform
            {
                angle += delta * 2.0f * (float)M_PI / 20.0f; // full rotation in 20 seconds
                angle = fmodf(angle, 2.0f * (float)M_PI);

                float aspect = (float)height / width;
                float matrix[] =
                {
                    cosf(angle) * aspect, -sinf(angle),
                    sinf(angle) * aspect,  cosf(angle),
                };

                GLint u_matrix = 0;
                glProgramUniformMatrix2fv(vshader, u_matrix, 1, GL_FALSE, matrix);
            }

            // activate shaders for next draw call
            glBindProgramPipeline(pipeline);

            // provide vertex input
            glBindVertexArray(vao);

            // bind texture to texture unit
            GLint s_texture = 0; // texture unit that sampler2D will use in GLSL code
            glBindTextureUnit(s_texture, texture);

            // draw 3 vertices as triangle
            glDrawArrays(GL_TRIANGLES, 0, 3);

            // swap the buffers to show output
            if (!eglSwapBuffers(display, surface))
            {
                FatalError("Failed to swap OpenGL buffers!");
            }
        }
        else
        {
            // window is minimized, cannot vsync - instead sleep a bit
            if (vsync)
            {
                usleep(10 * 1000);
            }
        }
    }
}

Thanks a lot, it helps a lot. I had to remove these lines to make it work on Ubuntu 20.04 x86_64 using NVIDIA 2070 GTX SUPER
//EGL_CONFIG_CAVEAT, EGL_NONE, //EGL_NATIVE_RENDERABLE, EGL_TRUE,

Thanks! Testing this on nvidia system was on my TODO list. I'll remove those two - they are not really needed.