screencast: remove swap_buffer function

Dequeuing a new buffer imidiately creates a problem when the buffer is
destroid while renegotiation of a valid modifier because we can end up using
a buffer which was freed while waiting for the buffer_done event. Then
xdpw will segfault when requesting a copy with a nonexisting buffer. To fix
this we can just dequeue a buffer right before we need it. This makes
the fallback via on_process obsolete since we dequeue the buffer at the
lates possible time.

include/pipewire_screencast.h

@@ -9,7 +9,6 @@
 
 void xdpw_pwr_dequeue_buffer(struct xdpw_screencast_instance *cast);
 void xdpw_pwr_enqueue_buffer(struct xdpw_screencast_instance *cast);
-void xdpw_pwr_swap_buffer(struct xdpw_screencast_instance *cast);
 void pwr_update_stream_param(struct xdpw_screencast_instance *cast);
 void xdpw_pwr_stream_create(struct xdpw_screencast_instance *cast);
 void xdpw_pwr_stream_destroy(struct xdpw_screencast_instance *cast);

include/screencast_common.h

@@ -144,7 +144,6 @@ struct xdpw_screencast_instance {
 	bool with_cursor;
 	int err;
 	bool quit;
-	bool need_buffer;
 	enum buffer_type buffer_type;
 
 	// fps limit

src/screencast/pipewire_screencast.c

@@ -111,18 +111,6 @@ static uint32_t build_formats(struct spa_pod_builder *b, struct xdpw_screencast_
 	return param_count;
 }
 
-static void pwr_handle_stream_on_process(void *data) {
-	logprint(TRACE, "pipewire: stream process");
-	struct xdpw_screencast_instance *cast = data;
-
-	if (cast->need_buffer) {
-		xdpw_pwr_dequeue_buffer(cast);
-		if (cast->current_frame.pw_buffer) {
-			cast->need_buffer = false;
-		}
-	}
-}
-
 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;
@@ -270,7 +258,6 @@ 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_on_process,
 };
 
 void xdpw_pwr_dequeue_buffer(struct xdpw_screencast_instance *cast) {
@@ -337,24 +324,6 @@ done:
 	cast->current_frame.pw_buffer = NULL;
 }
 
-void xdpw_pwr_swap_buffer(struct xdpw_screencast_instance *cast) {
-	logprint(TRACE, "pipewire: swapping buffers");
-
-	if (!cast->current_frame.pw_buffer) {
-		goto dequeue_buffer;
-	}
-
-	xdpw_pwr_enqueue_buffer(cast);
-
-dequeue_buffer:
-	assert(!cast->current_frame.pw_buffer);
-	cast->need_buffer = false;
-	xdpw_pwr_dequeue_buffer(cast);
-	if (!cast->current_frame.pw_buffer) {
-		cast->need_buffer = true;
-	}
-}
-
 void pwr_update_stream_param(struct xdpw_screencast_instance *cast) {
 	logprint(TRACE, "pipewire: stream update parameters");
 	struct pw_stream *stream = cast->stream;

src/screencast/screencast.c

@@ -70,7 +70,6 @@ void xdpw_screencast_instance_init(struct xdpw_screencast_context *ctx,
 	cast->with_cursor = with_cursor;
 	cast->refcount = 1;
 	cast->node_id = SPA_ID_INVALID;
-	cast->need_buffer = false;
 	wl_list_init(&cast->buffer_list);
 	logprint(INFO, "xdpw: screencast instance %p has %d references", cast, cast->refcount);
 	wl_list_insert(&ctx->screencast_instances, &cast->link);

src/screencast/wlr_screencast.c

@@ -51,7 +51,7 @@ void xdpw_wlr_frame_finish(struct xdpw_screencast_instance *cast) {
 	}
 
 	if (cast->frame_state == XDPW_FRAME_STATE_SUCCESS) {
-		xdpw_pwr_swap_buffer(cast);
+		xdpw_pwr_enqueue_buffer(cast);
 		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,
@@ -137,7 +137,6 @@ static void wlr_frame_buffer_done(void *data,
 		xdpw_pwr_dequeue_buffer(cast);
 	}
 
-	cast->need_buffer = false;
 	if (!cast->current_frame.xdpw_buffer) {
 		logprint(WARN, "wlroots: no current buffer");
 		xdpw_wlr_frame_finish(cast);