window: prevent EGL sub-surface deadlock

window: prevent EGL sub-surface deadlock

Mesa's eglSwapBuffers() waits for the frame event from the previous
swapBuffers, before it returns. Apparently eglSwapInterval(), which
should be able to disable the wait, is unimplemented for now.

When a sub-surface contains an EGL widget, and the commit mode is
synchronized, the frame events will not be delivered to EGL until the
parent surface gets committed. Therefore rendering the EGL widget twice
would lead to a deadlock.

When the window is being resized, we need to force a repaint of the EGL
widget, too, to make the whole window consistent. For that, we need to
make sure the frame event from the previous eglSwapBuffers() actually
arrives.

This patch adds an extra wl_surface.commit(parent), when the window is
being resized, which should guarantee, that the previous eglSwapBuffers
gets its event.

To properly handle an EGL widget in a sub-surface, running in its own
thread, the EGL widget's automatic updates should be paused before
sending the extra wl_surface.commit(parent). A natural place for the
pause would be in the widget's resize hook. However, wl_surface.commit
cannot be called right after resize hooks, because it would commit new,
incomplete surface state. Therefore this patch is not enough for
threaded toytoolkit applications.  Luckily those do not exist yet.

When eglSwapInterval() gets implemented, this patch should be reverted.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>