Corrections to alpha pipeline do_versions

Basically they're aimed to solve issues when scene with sky
was used for compositing. If compo used alpha output result
of current trunk would be completely different form hwo it
was before.

Two heuristics here:
- If there's no world or world color is black, it completely
  equals to straight alpha mode, no further magic is needed
  to preserve compatibility

- If scene is used as Render Layer node and something is
  connected to Alpha output of this node, ensure alpha mode
  for this scene is set to Premultiplied.

Basically it shall give better compatibility and make
4K mango project just happy! :)

1 files changed, 28 insertions, 0 deletions

diff --git a/source/blender/render/intern/source/pipeline.c b/source/blender/render/intern/source/pipeline.c
index 2c90110b458..d2b47a7bf4d 100644
--- a/source/blender/render/intern/source/pipeline.c
+++ b/source/blender/render/intern/source/pipeline.c
@@ -1355,6 +1355,19 @@ static int composite_needs_render(Scene *sce, int this_scene)
 	return 0;
 }
 
+static bool rlayer_node_uses_alpha(bNodeTree *ntree, bNode *node)
+{
+	bNodeSocket *sock;
+
+	for (sock = node->outputs.first; sock; sock = sock->next) {
+		/* Weak! but how to make it better? */
+		if (!strcmp(sock->name, "Alpha") && nodeCountSocketLinks(ntree, sock) > 0)
+			return true;
+	}
+
+	return false;
+}
+
 static void tag_scenes_for_render(Render *re)
 {
 	bNode *node;
@@ -1372,6 +1385,21 @@ static void tag_scenes_for_render(Render *re)
 	for (node = re->scene->nodetree->nodes.first; node; node = node->next) {
 		if (node->type == CMP_NODE_R_LAYERS) {
 			if (node->id) {
+				if (!MAIN_VERSION_ATLEAST(re->main, 265, 5)) {
+					if (rlayer_node_uses_alpha(re->scene->nodetree, node)) {
+						Scene *scene = (Scene*) node->id;
+
+						if (scene->r.alphamode != R_ALPHAPREMUL) {
+							BKE_reportf(re->reports, RPT_WARNING, "Setting scene %s alpha mode to Premul\n", scene->id.name + 2);
+
+							/* also print, so feedback is immediate */
+							printf("2.66 versioning fix: setting scene %s alpha mode to Premul\n", scene->id.name + 2);
+
+							scene->r.alphamode = R_ALPHAPREMUL;
+						}
+					}
+				}
+
 				if (node->id != (ID *)re->scene)
 					node->id->flag |= LIB_DOIT;
 			}