libstage: add return value to stage_render_func_t

This introduces some stage_render() flow control and render-time
freeing of nodes via the nodes render_func().

It's particularly useful for one-shot ephemeral nodes which are
thrown on-screen and require nothing more than their render and
free funcs for a full lifecycle.  An example would be something
running an effect briefly which runs autonomously from just a
timer alone, returning the free request from the final render once
the ending time arrives.

1 files changed, 21 insertions, 7 deletions

diff --git a/src/stage.c b/src/stage.c
index a714f1f..63afbcb 100644
--- a/src/stage.c
+++ b/src/stage.c
@@ -302,19 +302,33 @@ static void _prepare_stage(stage_t *stage, float alpha, void *render_ctxt)
 }
 
 
-static void _render_stage(const stage_t *stage, float alpha, void *render_ctxt)
+static void _render_stage(stage_t *stage, float alpha, void *render_ctxt)
 {
-	float	a = alpha * stage->alpha;
+	stage_render_func_ret_t	r = STAGE_RENDER_FUNC_RET_CONTINUE;
+	float			a;
 
 	assert(stage);
 
+	a = alpha * stage->alpha;
+
 	if (stage->ops->render_func)
-		stage->ops->render_func(stage, stage->object, a, render_ctxt);
+		r = stage->ops->render_func(stage, stage->object, a, render_ctxt);
+
+	switch (r) {
+	case STAGE_RENDER_FUNC_RET_FREE:
+		stage_free(stage);
+	case STAGE_RENDER_FUNC_RET_SKIP:
+		return;
+	case STAGE_RENDER_FUNC_RET_CONTINUE:
+		break;
+	default:
+		assert(0);
+	}
 
 	for (int i = 0; i < STAGE_LAYERS_MAX; i++) {
-		stage_t	*s;
+		stage_t	*s, *_s;
 
-		DLL_FOR_EACH_ENTRY(&stage->layers[i], s, stage_t, layer) {
+		DLL_FOR_EACH_ENTRY_SAFE(&stage->layers[i], s, _s, stage_t, layer) {
 			if (!s->active)
 				continue;
 
@@ -342,11 +356,11 @@ int stage_render(stage_t *stage, void *render_ctxt)
 		_prepare_stage(stage, 1.f, render_ctxt);
 
 	if (stage->dirty) {
+		stage->dirty = 0;
+
 		if (stage->active)
 			_render_stage(stage, 1.f, render_ctxt);
 
-		stage->dirty = 0;
-
 		return 1;
 	}