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output: avoid use of wlr_scene_output.WLR_PRIVATE.index

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We were only using it to allow quick bitset comparisons of sets of
outputs (such as view->outputs). We can maintain our own bit IDs for
this purpose and avoid using the private wlroots field.

Note: from my reading of wlr_scene_output_create(), it appears to
always take the lowest unused index, resulting in aggressive re-use of
index values when outputs are disconnected and reconnected. I've tried
to make re-use as infrequent as possible. This could theoretically
reduce the chance of a mix-up in view_update_outputs(), although I'm
not aware of any practical scenario where it matters.

v2: prevent adding more than 64 outputs
This commit is contained in:
John Lindgren 2025-11-25 17:36:02 -05:00 • committed by Consolatis
parent 6521067171
commit e96f4a032b
5 changed files with 59 additions and 4 deletions
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43
src/output.c
View file

@ -414,6 +414,41 @@ configure_new_output(struct server *server, struct output *output)
server->pending_output_layout_change--;
}
static uint64_t
get_unused_output_id_bit(struct server *server)
{
uint64_t used_id_bits = 0;
struct output *output;
wl_list_for_each(output, &server->outputs, link) {
used_id_bits |= output->id_bit;
}
if (used_id_bits == UINT64_MAX) {
return 0;
}
uint64_t id_bit = server->next_output_id_bit;
/*
* __builtin_popcountll() should be supported by GCC & clang.
* If it causes portability issues, just remove the assert.
*/
assert(__builtin_popcountll(id_bit) == 1);
while ((id_bit & used_id_bits) != 0) {
id_bit = (id_bit << 1) | (id_bit >> 63); /* rotate left */
}
/*
* The current implementation of view_update_outputs() isn't
* robust against ID bit re-use. Save the next bit here so we
* can cycle through all 64 available bits, making re-use less
* frequent (on a best-effort basis).
*/
server->next_output_id_bit = (id_bit << 1) | (id_bit >> 63);
return id_bit;
}
static void
handle_new_output(struct wl_listener *listener, void *data)
{
@ -437,6 +472,12 @@ handle_new_output(struct wl_listener *listener, void *data)
}
}
uint64_t id_bit = get_unused_output_id_bit(server);
if (!id_bit) {
wlr_log(WLR_ERROR, "Cannot add more than 64 outputs");
return;
}
if (wlr_output_is_wl(wlr_output)) {
char title[64];
snprintf(title, sizeof(title), "%s - %s", "labwc", wlr_output->name);
@ -487,6 +528,7 @@ handle_new_output(struct wl_listener *listener, void *data)
output->wlr_output = wlr_output;
wlr_output->data = output;
output->server = server;
output->id_bit = id_bit;
output_state_init(output);
wl_list_insert(&server->outputs, &output->link);
@ -583,6 +625,7 @@ output_init(struct server *server)
server->output_layout);
wl_list_init(&server->outputs);
server->next_output_id_bit = (1 << 0);
output_manager_init(server);
}

5
src/view.c
View file

@ -570,7 +570,7 @@ view_update_outputs(struct view *view)
wl_list_for_each(output, &view->server->outputs, link) {
if (output_is_usable(output) && wlr_output_layout_intersects(
layout, output->wlr_output, &view->current)) {
new_outputs |= (1ull << output->scene_output->WLR_PRIVATE.index);
new_outputs |= output->id_bit;
}
}
@ -586,8 +586,7 @@ view_on_output(struct view *view, struct output *output)
{
assert(view);
assert(output);
return output->scene_output
&& (view->outputs & (1ull << output->scene_output->WLR_PRIVATE.index));
return (view->outputs & output->id_bit) != 0;
}
void