Create a modern OpenGL context on Windows

gl_init.cpp

// Initializes an OpenGL device context for a given window.
void
gl_create_context(HWND hwnd)
{
    HDC   hdc;
    HGLRC hglrc;
    int   pfd_index;

    PIXELFORMATDESCRIPTOR pfd, device_pfd;

    // in order to load a modern opengl context we first need to load an old
    // opengl using a dummy window and use it to query the extension to load a
    // modern context.

    WNDCLASSA wndclass = {0};
    wndclass.lpfnWndProc = DefWindowProcA;
    wndclass.hInstance = GetModuleHandleA(NULL);
    wndclass.lpszClassName = "WNDWGLLOADER";

    RegisterClassA(&wndclass);
    HWND glwnd = CreateWindowA("WNDWGLLOADER", "",
            CS_OWNDC, 0, 0, 0, 0, NULL, NULL, wndclass.hInstance, NULL);

    if (!glwnd) {
        fprintf(stderr, "Failed to create dummy GL window (0x%lX)", GetLastError());
    }

    ZeroMemory(&pfd, sizeof(pfd));

    // we're doing this again later, for now all we care about is a PFD that
    // supports opengl
    pfd.nSize        = sizeof(PIXELFORMATDESCRIPTOR);
    pfd.nVersion     = 1;
    pfd.dwFlags      = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
    pfd.iPixelType   = PFD_TYPE_RGBA;
    pfd.cColorBits   = 32;
    pfd.cAlphaBits   = 8;
    pfd.cDepthBits   = 24;
    pfd.cStencilBits = 8;
    pfd.iLayerType   = PFD_MAIN_PLANE;

    hdc = GetDC(glwnd);
    pfd_index = ChoosePixelFormat(hdc, &pfd);
    DescribePixelFormat(hdc, pfd_index, sizeof(device_pfd), &device_pfd);

    if (!SetPixelFormat(hdc, pfd_index, &device_pfd)) {
        fprintf(stderr, "Failed to find a suitable pixel format for the graphics context (0x%lX).", GetLastError());
    }

    // create opengl device context for the current window
    hglrc = wglCreateContext(hdc);
    if (!wglMakeCurrent(hdc, hglrc)) {
        fprintf(stderr, "Failed to create an opengl context (0x%lX).", GetLastError());
    }

    // load the extensions we need in order to load the real context
    wglCreateContextAttribsARB = (wglCreateContextAttribsARB_t *)wglGetProcAddress("wglCreateContextAttribsARB");
    wglChoosePixelFormatARB = (wglChoosePixelFormatARB_t *)wglGetProcAddress("wglChoosePixelFormatARB");
    wglSwapIntervalEXT = (wglSwapIntervalEXT_t *)wglGetProcAddress("wglSwapIntervalEXT");

    if (!wglCreateContextAttribsARB || !wglChoosePixelFormatARB) {
        fprintf(stderr, "Failed to load opengl extensions");
    }

    wglMakeCurrent(hdc, 0);
    wglDeleteContext(hglrc);
    ReleaseDC(glwnd, hdc);
    DestroyWindow(glwnd);

    if (wglSwapIntervalEXT)
        wglSwapIntervalEXT(1);

    opengl32_dll = LoadLibraryA("opengl32.dll");
    if (!opengl32_dll) {
        fprintf(stderr, "Missing opengl32.dll (0x%lX)", GetLastError());
    }

    // do it for real this time

    hdc = GetDC(hwnd);
    ZeroMemory(&pfd, sizeof pfd);

    int pf_attribs[] = {
        WGL_DRAW_TO_WINDOW_ARB, GL_TRUE,
        WGL_SUPPORT_OPENGL_ARB, GL_TRUE,
        WGL_DOUBLE_BUFFER_ARB,  GL_TRUE,
        WGL_ACCELERATION_ARB,   WGL_FULL_ACCELERATION_ARB,
        WGL_PIXEL_TYPE_ARB,     WGL_TYPE_RGBA_ARB,
        WGL_COLOR_BITS_ARB,     32,
        WGL_DEPTH_BITS_ARB,     24,
        WGL_STENCIL_BITS_ARB,   8,
        0,
    };

    int context_attribs[] = {
        WGL_CONTEXT_MAJOR_VERSION_ARB, MV_MIN_GL_MAJOR_VERSION,
        WGL_CONTEXT_MINOR_VERSION_ARB, MV_MIN_GL_MINOR_VERSION,
        WGL_CONTEXT_PROFILE_MASK_ARB, WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
        0,
    } ;

    UINT n_formats;
    wglChoosePixelFormatARB(hdc, pf_attribs, NULL, 1, &pfd_index, &n_formats);
    if (n_formats == 0) {
        fprintf(stderr, "No suitable pixel format returned by wglChoosePixelFormatARB.");
    }

    DescribePixelFormat(hdc, pfd_index, sizeof(pfd), &pfd);
    if (!SetPixelFormat(hdc, pfd_index, &pfd)) {
        fprintf(stderr, "Failed to find a suitable pixel format for the graphics context (0x%lX).", GetLastError());
    }

    hglrc = wglCreateContextAttribsARB(hdc, 0, context_attribs);
    if (!wglMakeCurrent(hdc, hglrc)) {
        fprintf(stderr, "Failed to create an opengl context (0x%lX).", GetLastError());
    }

    ReleaseDC(hwnd, hdc);
}