Flip the display buffers

The implementation varies per platform.

Property definitions

	# Flip the display buffers
	#
	# The implementation varies per platform.
	fun flip do end

lib/gamnit/display.nit:67,2--70,16

	redef fun flip
	do
		assert glGetError == gl_NO_ERROR

		assert egl_display.is_valid

		egl_display.swap_buffers(window_surface)
	end

lib/gamnit/egl.nit:156,2--163,4