widnow setup

window_setup.gs

_xWindow = Gdk.X11Window.get_xid(area.get_window())
xDisplay = Gdk.X11Display.get_xdisplay(area.get_window().get_display())
_eglDisplay = eglGetDisplay(xDisplay)
xVisInfo = xDisplay.get_visual_info(0, xVisInfo, out matches)
visualid = (int) xVisInfo.visualid

// Copy X11 depth into EGL attributes
egl_attrs : array of EGLint = {
    EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,    // OpenGL ES 2.0
    EGL_NATIVE_VISUAL_ID, visualid,             // Use X11 VisualID
    EGL_DEPTH_SIZE, 16,                         // Depth
    EGL_STENCIL_SIZE, 1,                        // Stencil
    EGL_NONE
}

ctx_attrs : array of EGLint = {
    EGL_CONTEXT_CLIENT_VERSION, 2,              // OpenGL ES 2.0
    EGL_NONE
}

if not eglInitialize(_eglDisplay, out major, out minor)
    print "Failed to initialize EGL."
    return false

// Check EGL version
if major != 1 or minor < 3
    print "EGL version %i.%i not supported.", major, minor
    return false

if (!eglChooseConfig(_eglDisplay, egl_attrs, {_eglConfig}, out matches) 
    or matches == 0)
    print "EGL configuration failed."

eglBindAPI(EGL_OPENGL_ES_API)

_eglContext = eglCreateContext(_eglDisplay, _eglConfig,
                               EGL_NO_CONTEXT, ctx_attrs)
if _eglContext is EGL_NO_CONTEXT
    print("_eglContext is EGL_NO_CONTEXT")

// and before drawing
if _eglSurface is null
    // Get EGLSurface
    _eglSurface = eglCreateWindowSurface(_eglDisplay, _eglConfig,
                                         _xWindow, null)
    area.get_window().flush()
    if _eglSurface is EGL_NO_SURFACE
        print eglGetError().to_string()
        print "_eglSurface is EGL_NO_SURFACE"