simple-egl: Defer EGL surface/window creation

Rather than creating the wl_egl_window at the same time as wl_surface,
do it after we get the first configure event.

With it, we also defer eglMakeCurrent() as according to the spec, the
first time a OpenGL or OpenGL ES context is made current, the viewport
and scissor dimensions are set to the size of the draw surface.

This is particulary important when attempting to start simple-egl either
as fullscreen or as maximized, as not doing so will either incorrectly
commit a buffer with the original dimensions, and later on to resize to
the correct dimensions (which is the case for fullscreen), or it will
terminate the wayland connection abruptly due to xdg-shell protocol
violation, with a mismatch for the client's geometry (the case for
maximized).

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Suggested-by: Daniel Stone <daniel.stone@collabora.com>

clients/simple-egl.c

@@ -262,6 +262,19 @@ init_gl(struct window *window)
 	GLuint frag, vert;
 	GLuint program;
 	GLint status;
+	EGLBoolean ret;
+
+	window->native = wl_egl_window_create(window->surface,
+					      window->geometry.width,
+					      window->geometry.height);
+	window->egl_surface =
+		weston_platform_create_egl_surface(window->display->egl.dpy,
+						   window->display->egl.conf,
+						   window->native, NULL);
+
+	ret = eglMakeCurrent(window->display->egl.dpy, window->egl_surface,
+			     window->egl_surface, window->display->egl.ctx);
+	assert(ret == EGL_TRUE);
 
 	frag = create_shader(window, frag_shader_text, GL_FRAGMENT_SHADER);
 	vert = create_shader(window, vert_shader_text, GL_VERTEX_SHADER);
@@ -362,19 +375,9 @@ static void
 create_surface(struct window *window)
 {
 	struct display *display = window->display;
-	EGLBoolean ret;
 
 	window->surface = wl_compositor_create_surface(display->compositor);
 
-	window->native =
-		wl_egl_window_create(window->surface,
-				     window->geometry.width,
-				     window->geometry.height);
-	window->egl_surface =
-		weston_platform_create_egl_surface(display->egl.dpy,
-						   display->egl.conf,
-						   window->native, NULL);
-
 	window->xdg_surface = xdg_wm_base_get_xdg_surface(display->wm_base,
 							  window->surface);
 	xdg_surface_add_listener(window->xdg_surface,
@@ -392,10 +395,6 @@ create_surface(struct window *window)
 	window->wait_for_configure = true;
 	wl_surface_commit(window->surface);
 
-	ret = eglMakeCurrent(window->display->egl.dpy, window->egl_surface,
-			     window->egl_surface, window->display->egl.ctx);
-	assert(ret == EGL_TRUE);
-
 	if (!window->frame_sync)
 		eglSwapInterval(display->egl.dpy, 0);
 
@@ -866,7 +865,17 @@ main(int argc, char **argv)
 
 	init_egl(&display, &window);
 	create_surface(&window);
-	init_gl(&window);
+
+	/* we already have wait_for_configure set after create_surface() */
+	while (running && ret != -1 && window.wait_for_configure) {
+		ret = wl_display_dispatch(display.display);
+
+		/* wait until xdg_surface::configure acks the new dimensions */
+		if (window.wait_for_configure)
+			continue;
+
+		init_gl(&window);
+	}
 
 	display.cursor_surface =
 		wl_compositor_create_surface(display.compositor);
@@ -876,17 +885,9 @@ main(int argc, char **argv)
 	sigint.sa_flags = SA_RESETHAND;
 	sigaction(SIGINT, &sigint, NULL);
 
-	/* The mainloop here is a little subtle.  Redrawing will cause
-	 * EGL to read events so we can just call
-	 * wl_display_dispatch_pending() to handle any events that got
-	 * queued up as a side effect. */
 	while (running && ret != -1) {
-		if (window.wait_for_configure) {
-			ret = wl_display_dispatch(display.display);
-		} else {
-			ret = wl_display_dispatch_pending(display.display);
-			redraw(&window, NULL, 0);
-		}
+		ret = wl_display_dispatch_pending(display.display);
+		redraw(&window, NULL, 0);
 	}
 
 	fprintf(stderr, "simple-egl exiting\n");