protocol: wl_surface.frame needs wl_surface.commit

Clarify, when frame request takes effect.
Explain when to send/receive the callback.

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

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index e5c8c91..61bf268 100644 (file)
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -705,10 +705,20 @@
 
     <request name="frame">
       <description summary="request repaint feedback">
-       Request notification when the next frame is displayed.  Useful
+       Request notification when the next frame is displayed. Useful
        for throttling redrawing operations, and driving animations.
+       The frame request will take effect on the next wl_surface.commit.
        The notification will only be posted for one frame unless
        requested again.
+
+       A server should avoid signalling the frame callbacks if the
+       surface is not visible in any way, e.g. the surface is off-screen,
+       or completely obscured by other opaque surfaces.
+
+       A client can request a frame callback even without an attach,
+       damage, or any other state changes. wl_surface.commit triggers a
+       repaint, so the callback event will arrive after the next output
+       refresh where the surface is visible.
       </description>
 
       <arg name="callback" type="new_id" interface="wl_callback"/>