output-damage: refactor API

wlr_output_damage_make_current has been renamed to
wlr_output_damage_attach_render, since it's just a wrapper for
wlr_output_attach_render.

wlr_output_damage_swap_buffers has been removed completely. Instead,
wlr_output_damage now listens to successful wlr_output commits and updates its
internal state accordingly.

include/wlr/types/wlr_output.h

@@ -111,8 +111,10 @@ struct wlr_output {
 		// Emitted when buffers need to be swapped (because software cursors or
 		// fullscreen damage or because of backend-specific logic)
 		struct wl_signal needs_commit;
-		// Emitted right before buffer commit
+		// Emitted right before commit
 		struct wl_signal precommit; // wlr_output_event_precommit
+		// Emitted right after commit
+		struct wl_signal commit;
 		// Emitted right after the buffer has been presented to the user
 		struct wl_signal present; // wlr_output_event_present
 		struct wl_signal enable;

include/wlr/types/wlr_output_damage.h

@@ -24,10 +24,13 @@
 /**
  * Tracks damage for an output.
  *
- * When a `frame` event is emitted, `wlr_output_damage_make_current` should be
- * called. If necessary, the output should be repainted and
- * `wlr_output_damage_swap_buffers` should be called. No rendering should happen
- * outside a `frame` event handler.
+ * The `frame` event will be emitted when it is a good time for the compositor
+ * to submit a new frame.
+ *
+ * To render a new frame, compositors should call
+ * `wlr_output_damage_attach_render`, render and call `wlr_output_commit`. No
+ * rendering should happen outside a `frame` event handler or before
+ * `wlr_output_damage_attach_render`.
  */
 struct wlr_output_damage {
 	struct wlr_output *output;
@@ -50,25 +53,22 @@ struct wlr_output_damage {
 	struct wl_listener output_scale;
 	struct wl_listener output_needs_commit;
 	struct wl_listener output_frame;
+	struct wl_listener output_commit;
 };
 
 struct wlr_output_damage *wlr_output_damage_create(struct wlr_output *output);
 void wlr_output_damage_destroy(struct wlr_output_damage *output_damage);
 /**
- * Makes the output rendering context current. `needs_swap` is set to true if
- * `wlr_output_damage_swap_buffers` needs to be called. The region of the output
- * that needs to be repainted is added to `damage`.
- */
-bool wlr_output_damage_make_current(struct wlr_output_damage *output_damage,
-	bool *needs_swap, pixman_region32_t *damage);
-/**
- * Swaps the output buffers. If the time of the frame isn't known, set `when` to
- * NULL.
+ * Attach the renderer's buffer to the output. Compositors must call this
+ * function before rendering. After they are done rendering, they should call
+ * `wlr_output_set_damage` and `wlr_output_commit` to submit the new frame.
  *
- * Swapping buffers schedules a `frame` event.
+ * `needs_commit` will be set to true if a frame should be submitted. `damage`
+ * will be set to the region of the output that needs to be repainted, in
+ * output-buffer-local coordinates.
  */
-bool wlr_output_damage_swap_buffers(struct wlr_output_damage *output_damage,
-	struct timespec *when, pixman_region32_t *damage);
+bool wlr_output_damage_attach_render(struct wlr_output_damage *output_damage,
+	bool *needs_commit, pixman_region32_t *damage);
 /**
  * Accumulates damage and schedules a `frame` event.
  */

rootston/render.c

@@ -223,7 +223,7 @@ void output_render(struct roots_output *output) {
 	bool needs_swap;
 	pixman_region32_t damage;
 	pixman_region32_init(&damage);
-	if (!wlr_output_damage_make_current(output->damage, &needs_swap, &damage)) {
+	if (!wlr_output_damage_attach_render(output->damage, &needs_swap, &damage)) {
 		return;
 	}
 
@@ -310,7 +310,8 @@ renderer_end:
 		wlr_output_transform_invert(wlr_output->transform);
 	wlr_region_transform(&damage, &damage, transform, width, height);
 
-	if (!wlr_output_damage_swap_buffers(output->damage, &now, &damage)) {
+	wlr_output_set_damage(wlr_output, &damage);
+	if (!wlr_output_commit(wlr_output)) {
 		goto damage_finish;
 	}
 	output->last_frame = desktop->last_frame = now;
@@ -319,6 +320,5 @@ damage_finish:
 	pixman_region32_fini(&damage);
 
 	// Send frame done events to all surfaces
-	output_for_each_surface(output, surface_send_frame_done_iterator,
-		&now);
+	output_for_each_surface(output, surface_send_frame_done_iterator, &now);
 }

types/wlr_output.c

@@ -275,6 +275,7 @@ void wlr_output_init(struct wlr_output *output, struct wlr_backend *backend,
 	wl_signal_init(&output->events.frame);
 	wl_signal_init(&output->events.needs_commit);
 	wl_signal_init(&output->events.precommit);
+	wl_signal_init(&output->events.commit);
 	wl_signal_init(&output->events.present);
 	wl_signal_init(&output->events.enable);
 	wl_signal_init(&output->events.mode);
@@ -433,6 +434,8 @@ bool wlr_output_commit(struct wlr_output *output) {
 		wlr_surface_send_frame_done(cursor->surface, &now);
 	}
 
+	wlr_signal_emit_safe(&output->events.commit, output);
+
 	output->frame_pending = true;
 	output->needs_commit = false;
 	output_state_clear(&output->pending);

types/wlr_output_damage.c

@@ -51,6 +51,23 @@ static void output_handle_frame(struct wl_listener *listener, void *data) {
 	wlr_signal_emit_safe(&output_damage->events.frame, output_damage);
 }
 
+static void output_handle_commit(struct wl_listener *listener, void *data) {
+	struct wlr_output_damage *output_damage =
+		wl_container_of(listener, output_damage, output_commit);
+
+	if (!(output_damage->output->pending.committed & WLR_OUTPUT_STATE_BUFFER)) {
+		return;
+	}
+
+	// same as decrementing, but works on unsigned integers
+	output_damage->previous_idx += WLR_OUTPUT_DAMAGE_PREVIOUS_LEN - 1;
+	output_damage->previous_idx %= WLR_OUTPUT_DAMAGE_PREVIOUS_LEN;
+
+	pixman_region32_copy(&output_damage->previous[output_damage->previous_idx],
+		&output_damage->current);
+	pixman_region32_clear(&output_damage->current);
+}
+
 struct wlr_output_damage *wlr_output_damage_create(struct wlr_output *output) {
 	struct wlr_output_damage *output_damage =
 		calloc(1, sizeof(struct wlr_output_damage));
@@ -80,6 +97,8 @@ struct wlr_output_damage *wlr_output_damage_create(struct wlr_output *output) {
 	output_damage->output_needs_commit.notify = output_handle_needs_commit;
 	wl_signal_add(&output->events.frame, &output_damage->output_frame);
 	output_damage->output_frame.notify = output_handle_frame;
+	wl_signal_add(&output->events.commit, &output_damage->output_commit);
+	output_damage->output_commit.notify = output_handle_commit;
 
 	return output_damage;
 }
@@ -102,7 +121,7 @@ void wlr_output_damage_destroy(struct wlr_output_damage *output_damage) {
 	free(output_damage);
 }
 
-bool wlr_output_damage_make_current(struct wlr_output_damage *output_damage,
+bool wlr_output_damage_attach_render(struct wlr_output_damage *output_damage,
 		bool *needs_commit, pixman_region32_t *damage) {
 	struct wlr_output *output = output_damage->output;
 
@@ -141,26 +160,6 @@ bool wlr_output_damage_make_current(struct wlr_output_damage *output_damage,
 	return true;
 }
 
-bool wlr_output_damage_swap_buffers(struct wlr_output_damage *output_damage,
-		struct timespec *when, pixman_region32_t *damage) {
-	if (damage != NULL) {
-		wlr_output_set_damage(output_damage->output, damage);
-	}
-	if (!wlr_output_commit(output_damage->output)) {
-		return false;
-	}
-
-	// same as decrementing, but works on unsigned integers
-	output_damage->previous_idx += WLR_OUTPUT_DAMAGE_PREVIOUS_LEN - 1;
-	output_damage->previous_idx %= WLR_OUTPUT_DAMAGE_PREVIOUS_LEN;
-
-	pixman_region32_copy(&output_damage->previous[output_damage->previous_idx],
-		&output_damage->current);
-	pixman_region32_clear(&output_damage->current);
-
-	return true;
-}
-
 void wlr_output_damage_add(struct wlr_output_damage *output_damage,
 		pixman_region32_t *damage) {
 	int width, height;