screencast: don't use the PipeWire event to trigger screencast

Using the on_process event of the PipeWire can create a race condition
when a previous started screencast hasn't finished before the next
event.

include/pipewire_screencast.h

@@ -6,8 +6,6 @@
 #define XDPW_PWR_BUFFERS 4
 #define XDPW_PWR_ALIGN 16
 
-void xdpw_pwr_trigger_process(struct xdpw_screencast_instance *cast);
-bool xdpw_pwr_is_driving(struct xdpw_screencast_instance *cast);
 void xdpw_pwr_dequeue_buffer(struct xdpw_screencast_instance *cast);
 void xdpw_pwr_enqueue_buffer(struct xdpw_screencast_instance *cast);
 void pwr_update_stream_param(struct xdpw_screencast_instance *cast);

include/screencast_common.h

@@ -31,6 +31,7 @@ enum xdpw_chooser_types {
 
 enum xdpw_frame_state {
   XDPW_FRAME_STATE_NONE,
+  XDPW_FRAME_STATE_STARTED,
   XDPW_FRAME_STATE_RENEG,
   XDPW_FRAME_STATE_FAILED,
   XDPW_FRAME_STATE_SUCCESS,

src/screencast/pipewire_screencast.c

@@ -44,14 +44,6 @@ static struct spa_pod *build_format(struct spa_pod_builder *b, enum spa_video_fo
 	return spa_pod_builder_pop(b, &f[0]);
 }
 
-static void pwr_handle_stream_process(void *data) {
-	struct xdpw_screencast_instance *cast = data;
-
-	logprint(TRACE, "pipewire: stream process");
-
-	xdpw_wlr_frame_start(cast);
-}
-
 static void pwr_handle_stream_state_changed(void *data,
 		enum pw_stream_state old, enum pw_stream_state state, const char *error) {
 	struct xdpw_screencast_instance *cast = data;
@@ -64,7 +56,7 @@ static void pwr_handle_stream_state_changed(void *data,
 	switch (state) {
 	case PW_STREAM_STATE_STREAMING:
 		cast->pwr_stream_state = true;
-		if (!cast->wlr_frame) {
+		if (cast->frame_state == XDPW_FRAME_STATE_NONE) {
 			xdpw_wlr_frame_start(cast);
 		}
 		break;
@@ -184,17 +176,8 @@ static const struct pw_stream_events pwr_stream_events = {
 	.param_changed = pwr_handle_stream_param_changed,
 	.add_buffer = pwr_handle_stream_add_buffer,
 	.remove_buffer = pwr_handle_stream_remove_buffer,
-	.process = pwr_handle_stream_process,
 };
 
-void xdpw_pwr_trigger_process(struct xdpw_screencast_instance *cast) {
-	pw_stream_trigger_process(cast->stream);
-}
-
-bool xdpw_pwr_is_driving(struct xdpw_screencast_instance *cast) {
-	return pw_stream_is_driving(cast->stream);
-}
-
 void xdpw_pwr_dequeue_buffer(struct xdpw_screencast_instance *cast) {
 	logprint(TRACE, "pipewire: dequeueing buffer");
 

src/screencast/wlr_screencast.c

@@ -32,7 +32,11 @@ void xdpw_wlr_frame_finish(struct xdpw_screencast_instance *cast) {
 
 	wlr_frame_free(cast);
 
-	if (!cast->pwr_stream_state) {
+	if (cast->quit || cast->err) {
+		// TODO: revisit the exit condition (remove quit?)
+		// and clean up sessions that still exist if err
+		// is the cause of the instance_destroy call
+		xdpw_screencast_instance_destroy(cast);
 		return;
 	}
 
@@ -41,31 +45,24 @@ void xdpw_wlr_frame_finish(struct xdpw_screencast_instance *cast) {
 		xdpw_pwr_enqueue_buffer(cast);
 	}
 
+	if (!cast->pwr_stream_state) {
+		cast->frame_state = XDPW_FRAME_STATE_NONE;
+		return;
+	}
+
 	if (cast->frame_state == XDPW_FRAME_STATE_RENEG) {
 		pwr_update_stream_param(cast);
 	}
 
-	if (cast->quit || cast->err) {
+	if (cast->frame_state == XDPW_FRAME_STATE_SUCCESS) {
-		// TODO: revisit the exit condition (remove quit?)
+		uint64_t delay_ns = fps_limit_measure_end(&cast->fps_limit, cast->framerate);
-		// and clean up sessions that still exist if err
+		if (delay_ns > 0) {
-		// is the cause of the instance_destroy call
+			xdpw_add_timer(cast->ctx->state, delay_ns,
-		xdpw_screencast_instance_destroy(cast);
+				(xdpw_event_loop_timer_func_t) xdpw_wlr_frame_start, cast);
-		return ;
+			return;
-	}
-
-	if (cast->pwr_stream_state && xdpw_pwr_is_driving(cast)) {
-		if (cast->frame_state == XDPW_FRAME_STATE_SUCCESS) {
-			uint64_t delay_ns = fps_limit_measure_end(&cast->fps_limit, cast->framerate);
-			if (delay_ns > 0) {
-				xdpw_add_timer(cast->ctx->state, delay_ns,
-					(xdpw_event_loop_timer_func_t) xdpw_pwr_trigger_process, cast);
-			} else {
-				xdpw_pwr_trigger_process(cast);
-			}
-		} else {
-			xdpw_pwr_trigger_process(cast);
 		}
 	}
+	xdpw_wlr_frame_start(cast);
 }
 
 void xdpw_wlr_frame_start(struct xdpw_screencast_instance *cast) {
@@ -73,7 +70,7 @@ void xdpw_wlr_frame_start(struct xdpw_screencast_instance *cast) {
 	if (cast->err) {
 		logprint(ERROR, "wlroots: nonrecoverable error has happened. shutting down instance");
 		xdpw_screencast_instance_destroy(cast);
-		return ;
+		return;
 	}
 
 	if (cast->pwr_stream_state) {
@@ -81,11 +78,10 @@ void xdpw_wlr_frame_start(struct xdpw_screencast_instance *cast) {
 
 		if (!cast->current_frame.current_pw_buffer) {
 			logprint(WARN, "wlroots: failed to dequeue buffer");
-			// TODO: wait for next frame
 		}
 	}
 
-	cast->frame_state = XDPW_FRAME_STATE_NONE;
+	cast->frame_state = XDPW_FRAME_STATE_STARTED;
 	xdpw_wlr_register_cb(cast);
 }
 
@@ -121,11 +117,6 @@ static void wlr_frame_buffer_done(void *data,
 	struct xdpw_screencast_instance *cast = data;
 
 	logprint(TRACE, "wlroots: buffer_done event handler");
-	if (!cast->pwr_stream_state) {
-		xdpw_wlr_frame_finish(cast);
-		return;
-	}
-
 	if (!cast->current_frame.current_pw_buffer) {
 		logprint(WARN, "wlroots: no current buffer");
 		xdpw_wlr_frame_finish(cast);