From f2e5c4ffee3352268750861bd995386e1a47ecd5 Mon Sep 17 00:00:00 2001
From: "Kartik K. Agaram" <vc@akkartik.com>
Date: Tue, 5 Jul 2022 11:24:08 -0700
Subject: [PATCH] bugfix: avoid scrolling on 'end'

There's multiple ways to do this, only one of them is right, and I keep
forgetting what it is. Turn it into a method.
---
 main.lua |  3 +--
 text.lua | 20 ++++++++++++++------
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/main.lua b/main.lua
index 0446825..7321256 100644
--- a/main.lua
+++ b/main.lua
@@ -517,8 +517,7 @@ function App.keychord_pressed(chord, key)
         Text.insert_at_cursor(c)
       end
     end
-    App.draw()
-    if Cursor_y >= App.screen.height - Line_height then
+    if Text.cursor_past_screen_bottom() then
       Text.snap_cursor_to_bottom_of_screen()
     end
     schedule_save()
diff --git a/text.lua b/text.lua
index 7307056..4072311 100644
--- a/text.lua
+++ b/text.lua
@@ -509,7 +509,7 @@ function Text.end_of_line()
   Cursor1.pos = utf8.len(Lines[Cursor1.line].data) + 1
   local _,botpos = Text.pos_at_start_of_cursor_screen_line()
   local botline1 = {line=Cursor1.line, pos=botpos}
-  if Text.lt1(Screen_bottom1, botline1) then
+  if Text.cursor_past_screen_bottom() then
     Text.snap_cursor_to_bottom_of_screen()
   end
 end
@@ -575,9 +575,7 @@ function Text.right()
       end
     end
   end
-  local _,botpos = Text.pos_at_start_of_cursor_screen_line()
-  local botline1 = {line=Cursor1.line, pos=botpos}
-  if Text.lt1(Screen_bottom1, botline1) then
+  if Text.cursor_past_screen_bottom() then
     Text.snap_cursor_to_bottom_of_screen()
   end
 end
@@ -941,8 +939,7 @@ function Text.tweak_screen_top_and_cursor()
     Cursor1 = {line=Screen_top1.line, pos=Screen_top1.pos}
   elseif Cursor1.line >= Screen_bottom1.line then
 --?     print('too low')
-    App.draw()
-    if Text.lt1(Screen_bottom1, Cursor1) then
+    if Text.cursor_past_screen_bottom() then
 --?       print('tweak')
       local line = Lines[Screen_bottom1.line]
       Cursor1 = {line=Screen_bottom1.line, pos=Text.to_pos_on_line(line, App.screen.width-5, App.screen.height-5)}
@@ -950,6 +947,17 @@ function Text.tweak_screen_top_and_cursor()
   end
 end
 
+-- slightly expensive since it redraws the screen
+function Text.cursor_past_screen_bottom()
+  App.draw()
+  return Cursor_y >= App.screen.height - Line_height
+  -- this approach is cheaper and almost works, except on the final screen
+  -- where file ends above bottom of screen
+--?   local _,botpos = Text.pos_at_start_of_cursor_screen_line()
+--?   local botline1 = {line=Cursor1.line, pos=botpos}
+--?   return Text.lt1(Screen_bottom1, botline1)
+end
+
 function Text.redraw_all()
 --?   print('clearing fragments')
   for _,line in ipairs(Lines) do