play: introduce play_run_slice()HEADmaster

Sometimes a more granular main loop integration is required.
In such situations play_run() taking over is untenable, so this
splits out the body of play_run()'s loop as a separately callable
function.  Existing main loops can use this to run the play main
loop for a single slice.

The impetus for this has been experimenting with escripten
support in SARS, e.g.

emscripten_set_main_loop_arg((void(*)(void *))play_run_slice, play, -1, 1);

2 files changed, 27 insertions, 17 deletions

diff --git a/src/play.c b/src/play.c
index 5c51cbf..0a4630d 100644
--- a/src/play.c
+++ b/src/play.c
@@ -448,29 +448,38 @@ int play_shutdown(play_t *play)
 }
 
 
-void play_run(play_t *play)
+int play_run_slice(play_t *play)
 {
-	for (;;) {
-		SDL_Event	ev;
+	SDL_Event	ev;
 
-		do {
-			play->update_needed = 0;
+	do {
+		play->update_needed = 0;
 
-			if (play->ops[play->context]->update)
-				play->ops[play->context]->update(play, play->contexts[play->context]);
+		if (play->ops[play->context]->update)
+			play->ops[play->context]->update(play, play->contexts[play->context]);
 
-			/* see comment in play_context_enter() for why play->update_needed exists */
-		} while (play->update_needed);
+		/* see comment in play_context_enter() for why play->update_needed exists */
+	} while (play->update_needed);
 
-		if (play->ops[play->context]->render)
-			play->ops[play->context]->render(play, play->contexts[play->context]);
+	if (play->ops[play->context]->render)
+		play->ops[play->context]->render(play, play->contexts[play->context]);
 
-		while (!play->update_needed && SDL_PollEvent(&ev)) {
-			if (ev.type == SDL_APP_TERMINATING || ev.type == SDL_QUIT)
-				return;
+	while (!play->update_needed && SDL_PollEvent(&ev)) {
+		if (ev.type == SDL_APP_TERMINATING || ev.type == SDL_QUIT)
+			return 0;
 
-			if (play->ops[play->context]->dispatch)
-				play->ops[play->context]->dispatch(play, play->contexts[play->context], &ev);
-		}
+		if (play->ops[play->context]->dispatch)
+			play->ops[play->context]->dispatch(play, play->contexts[play->context], &ev);
+	}
+
+	return 1;
+}
+
+
+void play_run(play_t *play)
+{
+	for (;;) {
+		if (!play_run_slice(play))
+			return;
 	}
 }
diff --git a/src/play.h b/src/play.h
index 1d4ec6b..b3c56b5 100644
--- a/src/play.h
+++ b/src/play.h
@@ -57,6 +57,7 @@ typedef struct play_ops_t {
 
 play_t * play_startup(int argc, char *argv[], unsigned flags, const play_ops_t *ops[]);
 int play_shutdown(play_t *play);
+int play_run_slice(play_t *play);
 void play_run(play_t *play);
 
 void play_music_set(play_t *play, unsigned flags, const char *fmt, ...);