From ddf18060ab211320e19a5d9bd5886a3284c5a764 Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Fri, 3 Jun 2016 16:05:56 -0700
Subject: [PATCH] ui: register: keep scroll position more stable when toggling
 E

---
 hledger-ui/Hledger/UI/RegisterScreen.hs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/hledger-ui/Hledger/UI/RegisterScreen.hs b/hledger-ui/Hledger/UI/RegisterScreen.hs
index f733cce98..0fec0b940 100644
--- a/hledger-ui/Hledger/UI/RegisterScreen.hs
+++ b/hledger-ui/Hledger/UI/RegisterScreen.hs
@@ -83,7 +83,6 @@ initRegisterScreen d st@AppState{aopts=opts, ajournal=j, aScreen=s@RegisterScree
 
     -- keep the selection on the previously selected transaction if possible,
     -- (eg after toggling nonzero mode), otherwise select the last element.
-    -- XXX the scroll position should be disrupted less
     newl' = listMoveTo newselidx newl
       where
         newselidx = case listSelectedElement oldl of
@@ -221,7 +220,13 @@ handleRegisterScreen st@AppState{
         Right j' -> continue $ reload j' d st
         Left err -> continue $ screenEnter d ES.screen{esState=err} st
 
-    Vty.EvKey (Vty.KChar 'E') [] -> continue $ reload j d $ stToggleEmpty st
+    Vty.EvKey (Vty.KChar 'E') [] -> do
+      -- encourage a more stable scroll position when toggling items.
+      -- We scroll to the beginning, then the viewport automatically
+      -- scrolls down just far enough to reveal the selection.
+      vScrollToBeginning $ viewportScroll "register"
+      continue $ reload j d $ stToggleEmpty st
+
     Vty.EvKey (Vty.KChar 'C') [] -> continue $ reload j d $ stToggleCleared st
     Vty.EvKey (Vty.KChar 'R') [] -> continue $ reload j d $ stToggleReal st