BLI_listbase: Add/use utility to move link (BLI_listbase_link_move)

We were calling BLI_remlink and then BLI_insertlinkbefore/after quite often. BLI_listbase_link_move simplifies code a bit and makes it easier to follow. It also returns if link position has changed which can be used to avoid unnecessary updates.

Added it to a number of list reorder operators for now and made use of return value. Behavior shouldn't be changed.

Also some minor cleanup.

1 files changed, 38 insertions, 0 deletions

diff --git a/source/blender/blenlib/intern/listbase.c b/source/blender/blenlib/intern/listbase.c
index ebee2c7941c..e72eff57ad9 100644
--- a/source/blender/blenlib/intern/listbase.c
+++ b/source/blender/blenlib/intern/listbase.c
@@ -342,6 +342,44 @@ void BLI_insertlinkbefore(ListBase *listbase, void *vnextlink, void *vnewlink)
 	}
 }
 
+/**
+ * Reinsert \a link relative to its current position but offset by \a step. Doesn't move
+ * item if new position would exceed list (could optionally move to head/tail).
+ *
+ * \param step: Absolute value defines step size, sign defines direction. E.g pass -1
+ *              to move \a link before previous, or 1 to move behind next.
+ * \return If position of \a link has changed.
+ */
+bool BLI_listbase_link_move(ListBase *listbase, void *vlink, int step)
+{
+	Link *link = vlink;
+	Link *hook = link;
+	const bool is_up = step < 0;
+
+	if (step == 0 || vlink == NULL) {
+		return false;
+	}
+	BLI_assert(BLI_findindex(listbase, link) != -1);
+
+	/* find link to insert before/after */
+	for (int i = 0; i < ABS(step); i++) {
+		hook = is_up ? hook->prev : hook->next;
+		if (!hook) {
+			return false;
+		}
+	}
+
+	/* reinsert link */
+	BLI_remlink(listbase, vlink);
+	if (is_up) {
+		BLI_insertlinkbefore(listbase, hook, vlink);
+	}
+	else {
+		BLI_insertlinkafter(listbase, hook, vlink);
+	}
+	return true;
+}
+
 
 /**
  * Removes and disposes of the entire contents of listbase using direct free(3).