Bake-API: Test for cyclic node connection

If the active image node contributes to the final material shader
(meaning it's either directly or indirectly connected to an Output Node)
the user will receive an alert about circular dependency.

Similar to what we do for Blender internal the baking will still happen,
but the user will receive the alert which should prevent the image
saving to happen if the result was not intentional.

Core function to check for node output written by Lukas Toenne.

Reviewers: lukastoenne, campbellbarton

Differential Revision: https://developer.blender.org/D673

8 files changed, 63 insertions, 10 deletions

diff --git a/source/blender/blenkernel/BKE_node.h b/source/blender/blenkernel/BKE_node.h
index c81133a85fa..15e7efe7c6e 100644
--- a/source/blender/blenkernel/BKE_node.h
+++ b/source/blender/blenkernel/BKE_node.h
@@ -585,6 +585,9 @@ void            node_type_gpu(struct bNodeType *ntype, NodeGPUExecFunction gpufu
 void            node_type_internal_links(struct bNodeType *ntype, void (*update_internal_links)(struct bNodeTree *, struct bNode *));
 void            node_type_compatibility(struct bNodeType *ntype, short compatibility);
 
+/* ************** GENERIC NODE FUNCTIONS *************** */
+bool BKE_node_is_connected_to_output(struct bNodeTree *ntree, struct bNode *node);
+
 /* ************** COMMON NODES *************** */
 
 #define NODE_UNDEFINED	-2		/* node type is not registered */
diff --git a/source/blender/editors/include/ED_uvedit.h b/source/blender/editors/include/ED_uvedit.h
index 04eb829979f..4b82fa40c6a 100644
--- a/source/blender/editors/include/ED_uvedit.h
+++ b/source/blender/editors/include/ED_uvedit.h
@@ -54,7 +54,7 @@ void ED_uvedit_assign_image(struct Main *bmain, struct Scene *scene, struct Obje
 bool ED_uvedit_minmax(struct Scene *scene, struct Image *ima, struct Object *obedit, float min[2], float max[2]);
 
 bool ED_object_get_active_image(struct Object *ob, int mat_nr,
-                                struct Image **r_ima, struct ImageUser **r_iuser, struct bNode **r_node);
+                                struct Image **r_ima, struct ImageUser **r_iuser, struct bNode **r_node, struct bNodeTree **r_ntree);
 void ED_object_assign_active_image(struct Main *bmain, struct Object *ob, int mat_nr, struct Image *ima);
 
 bool ED_uvedit_test(struct Object *obedit);
diff --git a/source/blender/editors/object/object_bake_api.c b/source/blender/editors/object/object_bake_api.c
index f26425943bd..b3f3a562998 100644
--- a/source/blender/editors/object/object_bake_api.c
+++ b/source/blender/editors/object/object_bake_api.c
@@ -51,6 +51,7 @@
 #include "BKE_image.h"
 #include "BKE_library.h"
 #include "BKE_main.h"
+#include "BKE_node.h"
 #include "BKE_report.h"
 #include "BKE_modifier.h"
 #include "BKE_mesh.h"
@@ -367,10 +368,22 @@ static bool bake_object_check(Object *ob, ReportList *reports)
 	}
 
 	for (i = 0; i < ob->totcol; i++) {
-		ED_object_get_active_image(ob, i + 1, &image, NULL, NULL);
+		bNodeTree *ntree = NULL;
+		bNode *node = NULL;
+		ED_object_get_active_image(ob, i + 1, &image, NULL, &node, &ntree);
 
 		if (image) {
-			ImBuf *ibuf = BKE_image_acquire_ibuf(image, NULL, &lock);
+			ImBuf *ibuf;
+
+			if (node) {
+				if (BKE_node_is_connected_to_output(ntree, node)) {
+					BKE_reportf(reports, RPT_ERROR,
+					            "Circular dependency for image \"%s\" from object \"%s\"",
+					            image->id.name + 2, ob->id.name + 2);
+				}
+			}
+
+			ibuf = BKE_image_acquire_ibuf(image, NULL, &lock);
 
 			if (ibuf) {
 				BKE_image_release_ibuf(image, ibuf, lock);
@@ -477,7 +490,7 @@ static void build_image_lookup(Main *bmain, Object *ob, BakeImages *bake_images)
 
 	for (i = 0; i < tot_mat; i++) {
 		Image *image;
-		ED_object_get_active_image(ob, i + 1, &image, NULL, NULL);
+		ED_object_get_active_image(ob, i + 1, &image, NULL, NULL, NULL);
 
 		if ((image->id.flag & LIB_DOIT)) {
 			for (j = 0; j < i; j++) {
diff --git a/source/blender/editors/space_view3d/drawmesh.c b/source/blender/editors/space_view3d/drawmesh.c
index 348e6e526fe..89babf977e1 100644
--- a/source/blender/editors/space_view3d/drawmesh.c
+++ b/source/blender/editors/space_view3d/drawmesh.c
@@ -941,7 +941,7 @@ static void tex_mat_set_texture_cb(void *userData, int mat_nr, void *attribs)
 	int texture_set = 0;
 
 	/* draw image texture if we find one */
-	if (ED_object_get_active_image(data->ob, mat_nr, &ima, &iuser, &node)) {
+	if (ED_object_get_active_image(data->ob, mat_nr, &ima, &iuser, &node, NULL)) {
 		/* get openl texture */
 		int mipmap = 1;
 		int bindcode = (ima) ? GPU_verify_image(ima, iuser, 0, 0, mipmap, false) : 0;
diff --git a/source/blender/editors/uvedit/uvedit_draw.c b/source/blender/editors/uvedit/uvedit_draw.c
index 6eb8e525c96..0f605429187 100644
--- a/source/blender/editors/uvedit/uvedit_draw.c
+++ b/source/blender/editors/uvedit/uvedit_draw.c
@@ -424,7 +424,7 @@ static void draw_uvs_other_mesh_new_shading(Object *ob, const Image *curimage)
 		
 		/* if no materials, assume a default material with no image */
 		if (ob->totcol)
-			ED_object_get_active_image(ob, a + 1, &image, NULL, NULL);
+			ED_object_get_active_image(ob, a + 1, &image, NULL, NULL, NULL);
 		else
 			image = NULL;
 
@@ -577,7 +577,7 @@ static void draw_uvs(SpaceImage *sima, Scene *scene, Object *obedit)
 
 		if (new_shading_nodes) {
 			if (efa_act) {
-				ED_object_get_active_image(obedit, efa_act->mat_nr + 1, &curimage, NULL, NULL);
+				ED_object_get_active_image(obedit, efa_act->mat_nr + 1, &curimage, NULL, NULL, NULL);
 			}
 			else {
 				curimage = ima;
diff --git a/source/blender/editors/uvedit/uvedit_ops.c b/source/blender/editors/uvedit/uvedit_ops.c
index ed88c72edc4..0d8b5a524b6 100644
--- a/source/blender/editors/uvedit/uvedit_ops.c
+++ b/source/blender/editors/uvedit/uvedit_ops.c
@@ -137,21 +137,24 @@ static bool is_image_texture_node(bNode *node)
 }
 
 bool ED_object_get_active_image(Object *ob, int mat_nr,
-                                Image **r_ima, ImageUser **r_iuser, bNode **r_node)
+                                Image **r_ima, ImageUser **r_iuser, bNode **r_node, bNodeTree **r_ntree)
 {
 	Material *ma = give_current_material(ob, mat_nr);
-	bNode *node = (ma && ma->use_nodes) ? nodeGetActiveTexture(ma->nodetree) : NULL;
+	bNodeTree *ntree = (ma && ma->use_nodes) ? ma->nodetree : NULL;
+	bNode *node = (ntree) ? nodeGetActiveTexture(ntree) : NULL;
 
 	if (node && is_image_texture_node(node)) {
 		if (r_ima) *r_ima = (Image *)node->id;
 		if (r_iuser) *r_iuser = NULL;
 		if (r_node) *r_node = node;
+		if (r_ntree) *r_ntree = ntree;
 		return true;
 	}
 	
 	if (r_ima) *r_ima = NULL;
 	if (r_iuser) *r_iuser = NULL;
 	if (r_node) *r_node = node;
+	if (r_ntree) *r_ntree = ntree;
 
 	return false;
 }
diff --git a/source/blender/editors/uvedit/uvedit_unwrap_ops.c b/source/blender/editors/uvedit/uvedit_unwrap_ops.c
index 7442e7b6411..335d8e6589e 100644
--- a/source/blender/editors/uvedit/uvedit_unwrap_ops.c
+++ b/source/blender/editors/uvedit/uvedit_unwrap_ops.c
@@ -201,7 +201,7 @@ void uvedit_get_aspect(Scene *scene, Object *ob, BMEditMesh *em, float *aspx, fl
 
 	if (efa) {
 		if (BKE_scene_use_new_shading_nodes(scene)) {
-			ED_object_get_active_image(ob, efa->mat_nr + 1, &ima, NULL, NULL);
+			ED_object_get_active_image(ob, efa->mat_nr + 1, &ima, NULL, NULL, NULL);
 		}
 		else {
 			MTexPoly *tf = CustomData_bmesh_get(&em->bm->pdata, efa->head.data, CD_MTEXPOLY);
diff --git a/source/blender/nodes/intern/node_common.c b/source/blender/nodes/intern/node_common.c
index ae834f9e7cc..c58c9c902ec 100644
--- a/source/blender/nodes/intern/node_common.c
+++ b/source/blender/nodes/intern/node_common.c
@@ -336,6 +336,40 @@ void ntree_update_reroute_nodes(bNodeTree *ntree)
 			node_reroute_inherit_type_recursive(ntree, node);
 }
 
+static bool node_is_connected_to_output_recursive(bNodeTree *ntree, bNode *node)
+{
+	bNodeLink *link;
+
+	/* avoid redundant checks, and infinite loops in case of cyclic node links */
+	if (node->done)
+		return false;
+	node->done = 1;
+
+	/* main test, done before child loop so it catches output nodes themselves as well */
+	if (node->typeinfo->nclass == NODE_CLASS_OUTPUT && node->flag & NODE_DO_OUTPUT)
+		return true;
+
+	/* test all connected nodes, first positive find is sufficient to return true */
+	for (link = ntree->links.first; link; link = link->next) {
+		if (link->fromnode == node) {
+			if (node_is_connected_to_output_recursive(ntree, link->tonode))
+				return true;
+		}
+	}
+	return false;
+}
+
+bool BKE_node_is_connected_to_output(bNodeTree *ntree, bNode *node)
+{
+	bNode *tnode;
+
+	/* clear flags */
+	for (tnode = ntree->nodes.first; tnode; tnode = tnode->next)
+		tnode->done = 0;
+
+	return node_is_connected_to_output_recursive(ntree, node);
+}
+
 void BKE_node_tree_unlink_id(ID *id, struct bNodeTree *ntree)
 {
 	bNode *node;