From bbd4cbef788140c5e992abf56eb54576e09ccdb7 Mon Sep 17 00:00:00 2001
From: Thomas Goyne <plorkyeran@aegisub.org>
Date: Mon, 30 Sep 2013 17:01:15 -0700
Subject: [PATCH] Fix shifting contiguous selections downward

Reverse iterators behave differently from regular iterators when
swapping (regular iterators continue to point at the same elements,
while reverse iterators do not), so instead use regular iterators with a
negative step for shifting down.
---
 aegisub/src/command/grid.cpp | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/aegisub/src/command/grid.cpp b/aegisub/src/command/grid.cpp
index 55a7d3544..6eb341c6d 100644
--- a/aegisub/src/command/grid.cpp
+++ b/aegisub/src/command/grid.cpp
@@ -350,18 +350,19 @@ struct grid_tags_simplify : public Command {
 };
 
 template<class T, class U>
-static bool move_one(T begin, T end, U const& value) {
+static bool move_one(T begin, T end, U const& to_move, int step) {
 	size_t move_count = 0;
-	T prev = end;
-	for (; begin != end; ++begin) {
-		typename U::key_type cur = dynamic_cast<typename U::key_type>(&*begin);
-		bool in_set = !!value.count(cur);
-		if (!in_set && cur)
-			prev = begin;
-		else if (in_set && prev != end) {
-			begin->swap_nodes(*prev);
-			prev = begin;
-			if (++move_count == value.size())
+	auto prev = end;
+	for (auto it = begin; it != end; std::advance(it, step)) {
+		auto cur = dynamic_cast<typename U::key_type>(&*it);
+		if (!cur) continue;
+
+		if (!to_move.count(cur))
+			prev = it;
+		else if (prev != end) {
+			it->swap_nodes(*prev);
+			prev = it;
+			if (++move_count == to_move.size())
 				break;
 		}
 	}
@@ -382,7 +383,7 @@ struct grid_move_up : public Command {
 	}
 
 	void operator()(agi::Context *c) {
-		if (move_one(c->ass->Line.begin(), c->ass->Line.end(), c->selectionController->GetSelectedSet()))
+		if (move_one(c->ass->Line.begin(), c->ass->Line.end(), c->selectionController->GetSelectedSet(), 1))
 			c->ass->Commit(_("move lines"), AssFile::COMMIT_ORDER);
 	}
 };
@@ -400,7 +401,7 @@ struct grid_move_down : public Command {
 	}
 
 	void operator()(agi::Context *c) {
-		if (move_one(c->ass->Line.rbegin(), c->ass->Line.rend(), c->selectionController->GetSelectedSet()))
+		if (move_one(--c->ass->Line.end(), c->ass->Line.begin(), c->selectionController->GetSelectedSet(), -1))
 			c->ass->Commit(_("move lines"), AssFile::COMMIT_ORDER);
 	}
 };