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libweston: improve weston_output_disable() comments

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Reorder some paragraphs to be more logically ordered. Rewrite the
description of the backend-specific disable function to explain the
semantics instead of the mechanics. Remove the paragraph about
pending_output_list as unnecessary details.

Add a big fat comment on why we call output->disable() always instead of
only for actually enabled outputs.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Armin Krezović <krezovic.armin@gmail.com>
This commit is contained in:
Pekka Paalanen 2017-03-29 15:45:46 +03:00
parent 08d4edf20d
commit c65df6403a
1 changed files with 17 additions and 15 deletions
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32
libweston/compositor.c
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@ -4764,28 +4764,22 @@ weston_output_enable(struct weston_output *output)
*
* \param output The weston_output object that needs to be disabled.
*
* See weston_output_init() for more information on the
* state output is returned to.
*
* Calls a backend specific function to disable an output, in case
* such function exists.
*
* If the output is being used by the compositor, it is first removed
* The backend specific disable function may choose to postpone the disabling
* by returning a negative value, in which case this function returns early.
* In that case the backend will guarantee the output will be disabled soon
* by the backend calling this function again. One must not attempt to re-enable
* the output until that happens.
*
* Otherwise, if the output is being used by the compositor, it is removed
* from weston's output_list (see weston_compositor_remove_output())
* and is returned to a state it was before weston_output_enable()
* was ran (see weston_output_enable_undo()).
*
* Output is added to pending_output_list so it will get destroyed
* if the output does not get configured again when the compositor
* shuts down. If an output is to be used immediately, it needs to
* be manually removed from the list (the compositor specific functions
* for handling pending outputs will take care of that).
*
* If backend specific disable function returns negative value,
* this function will return too. It can be used as an indicator
* that output cannot be disabled at the present time. In that case
* backend needs to make sure the output is disabled when it is
* possible.
* See weston_output_init() for more information on the
* state output is returned to.
*/
WL_EXPORT void
weston_output_disable(struct weston_output *output)
@ -4795,6 +4789,14 @@ weston_output_disable(struct weston_output *output)
/* Should we rename this? */
output->destroying = 1;
/* Disable is called unconditionally also for not-enabled outputs,
* because at compositor start-up, if there is an output that is
* already on but the compositor wants to turn it off, we have to
* forward the turn-off to the backend so it knows to do it.
* The backend cannot initially turn off everything, because it
* would cause unnecessary mode-sets for all outputs the compositor
* wants to be on.
*/
if (output->disable(output) < 0)
return;