How to create a window and fill it with color using OpenES 2.0 + X11?

Question

I googled as hard as I can, but I found nothing.

What I want to do:

• create a window with X11 (Xlib) and show it
• fill the window with color using OpenGL ES 2.0

For OpenGL ES 2.0 support on my ArchLinux, I use MESA. I know how to create a simple X window using Xlib, I have a basic knowledge of EGL and OpenGL ES, but I can't understand how to use all them (X11 + EGL + OpenGL ES 2.0) in conjuction.

I would be very thakful if someone wrote at least a short code example on how to prepare a X window and connect it with OpenGL ES 2.0 correctly and start rendering.

Answer 1

Create Window:

Window root;
XSetWindowAttributes swa;
XSetWindowAttributes  xattr;
Atom wm_state;
XWMHints hints;
XEvent xev;
EGLConfig ecfg;
EGLint num_config;
Window win;

/*
 * X11 native display initialization
 */

x_display = XOpenDisplay(NULL);
if ( x_display == NULL )
{
    return EGL_FALSE;
}

root = DefaultRootWindow(x_display);

swa.event_mask  =  ExposureMask | PointerMotionMask | KeyPressMask;
win = XCreateWindow(
           x_display, root,
           0, 0, esContext->width, esContext->height, 0,
           CopyFromParent, InputOutput,
           CopyFromParent, CWEventMask,
           &swa );

xattr.override_redirect = FALSE;
XChangeWindowAttributes ( x_display, win, CWOverrideRedirect, &xattr );

hints.input = TRUE;
hints.flags = InputHint;
XSetWMHints(x_display, win, &hints);

// make the window visible on the screen
XMapWindow (x_display, win);
XStoreName (x_display, win, title);

// get identifiers for the provided atom name strings
wm_state = XInternAtom (x_display, "_NET_WM_STATE", FALSE);

memset ( &xev, 0, sizeof(xev) );
xev.type                 = ClientMessage;
xev.xclient.window       = win;
xev.xclient.message_type = wm_state;
xev.xclient.format       = 32;
xev.xclient.data.l[0]    = 1;
xev.xclient.data.l[1]    = FALSE;
XSendEvent (
   x_display,
   DefaultRootWindow ( x_display ),
   FALSE,
   SubstructureNotifyMask,
   &xev );

Set color:

   glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
   // Set the viewport
   glViewport ( 0, 0, esContext->width, esContext->height );

   // Clear the color buffer
   glClear ( GL_COLOR_BUFFER_BIT );

Sources:

• https://github.com/danginsburg/opengles-book-samples/blob/master/LinuxX11/Chapter_2/Hello_Triangle/Hello_Triangle.c
• https://github.com/danginsburg/opengles-book-samples/blob/master/LinuxX11/Common/esUtil.c
• https://github.com/danginsburg/opengles-book-samples/blob/master/LinuxX11/Common/esUtil.h

Answer 2

The opengles-book-samples code actually fails for me. If you see the same init failures, a call to eglBindAPI(EGL_OPENGL_ES_API) seemed to fix it.