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wlr_scene: fix fullscreen app stuttering when screensharing

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Problem: The wlroots implementation of wlr_screencopy applys a lock for
a brief duration every time a frame is captured. If an output is
eligible for direct scanout then this will result in direct scanout
being rapidly toggled on and off since the lock count constantly flips
between 0 and 1. On some hardware this causes stuttering every time
direct scanout is enabled then disabled.

Solution: To mitigate this we wait for there to be 0 locks for 120
frames so that we can be relatively confident that screen recording has
stopped before we re-enable direct scanout.
This commit is contained in:
Gabriel Ford 2025-10-12 14:47:23 -04:00
parent 19c5d22beb
commit 06d3d48aa2
3 changed files with 20 additions and 1 deletions
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2
include/wlr/types/wlr_output.h
View file

@ -248,6 +248,8 @@ struct wlr_output {
int attach_render_locks; // number of locks forcing rendering int attach_render_locks; // number of locks forcing rendering
int frames_since_locked;
struct wl_list cursors; // wlr_output_cursor.link struct wl_list cursors; // wlr_output_cursor.link
struct wlr_output_cursor *hardware_cursor; struct wlr_output_cursor *hardware_cursor;
struct wlr_swapchain *cursor_swapchain; struct wlr_swapchain *cursor_swapchain;

1
types/output/output.c
View file

@ -341,6 +341,7 @@ void wlr_output_init(struct wlr_output *output, struct wlr_backend *backend,
.transform = WL_OUTPUT_TRANSFORM_NORMAL, .transform = WL_OUTPUT_TRANSFORM_NORMAL,
.scale = 1, .scale = 1,
.commit_seq = 0, .commit_seq = 0,
.frames_since_locked = 0,
}; };
wl_list_init(&output->modes); wl_list_init(&output->modes);

18
types/scene/wlr_scene.c
View file

@ -30,6 +30,15 @@
#define DMABUF_FEEDBACK_DEBOUNCE_FRAMES 30 #define DMABUF_FEEDBACK_DEBOUNCE_FRAMES 30
#define HIGHLIGHT_DAMAGE_FADEOUT_TIME 250 #define HIGHLIGHT_DAMAGE_FADEOUT_TIME 250
// wlroot's implementation of wlr_screencopy applys a lock for a brief duration
// every time a frame is captured. If an output is eligible for direct scanout
// then this will result in direct scanout being rapidly toggled on and off
// since the lock count constantly flips between 0 and 1. On some hardware this
// causes stuttering every time direct scanout is enabled then disabled.
//
// To mitigate this we wait for there to be 0 locks for 120 frames so that we
// can be relatively confident that screen recording has stopped.
#define SCANOUT_UNLOCK_FRAMES 120
struct wlr_scene_tree *wlr_scene_tree_from_node(struct wlr_scene_node *node) { struct wlr_scene_tree *wlr_scene_tree_from_node(struct wlr_scene_node *node) {
assert(node->type == WLR_SCENE_NODE_TREE); assert(node->type == WLR_SCENE_NODE_TREE);
@ -2240,12 +2249,19 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
wlr_output_state_set_damage(state, &scene_output->pending_commit_damage); wlr_output_state_set_damage(state, &scene_output->pending_commit_damage);
if (output->attach_render_locks > 0) {
output->frames_since_locked = 0;
} else if (output->attach_render_locks <= SCANOUT_UNLOCK_FRAMES) {
output->frames_since_locked++;
}
// We only want to try direct scanout if: // We only want to try direct scanout if:
// - We are confident that the screen isn't being captured
// - There is only one entry in the render list // - There is only one entry in the render list
// - There are no color transforms that need to be applied // - There are no color transforms that need to be applied
// - Damage highlight debugging is not enabled // - Damage highlight debugging is not enabled
enum scene_direct_scanout_result scanout_result = SCANOUT_INELIGIBLE; enum scene_direct_scanout_result scanout_result = SCANOUT_INELIGIBLE;
if (options->color_transform == NULL && list_len == 1 if (output->frames_since_locked > SCANOUT_UNLOCK_FRAMES
&& options->color_transform == NULL && list_len == 1
&& debug_damage != WLR_SCENE_DEBUG_DAMAGE_HIGHLIGHT) { && debug_damage != WLR_SCENE_DEBUG_DAMAGE_HIGHLIGHT) {
scanout_result = scene_entry_try_direct_scanout(&list_data[0], state, &render_data); scanout_result = scene_entry_try_direct_scanout(&list_data[0], state, &render_data);
} }