diff --git a/edit.lua b/edit.lua
index 566efb7..f5ea9bd 100644
--- a/edit.lua
+++ b/edit.lua
@@ -133,13 +133,13 @@ function edit.draw(State)
       button('draw', {x=4,y=y+4, w=12,h=12, color={1,1,0},
         icon = icon.insert_drawing,
         onpress1 = function()
-                     Drawing.before = snapshot(line_index-1, line_index)
+                     Drawing.before = snapshot(State, line_index-1, line_index)
                      table.insert(State.lines, line_index, {mode='drawing', y=y, h=256/2, points={}, shapes={}, pending={}})
                      if State.cursor1.line >= line_index then
                        State.cursor1.line = State.cursor1.line+1
                      end
                      schedule_save(State)
-                     record_undo_event({before=Drawing.before, after=snapshot(line_index-1, line_index+1)})
+                     record_undo_event(State, {before=Drawing.before, after=snapshot(State, line_index-1, line_index+1)})
                    end
       })
       if State.search_term == nil then
@@ -227,7 +227,7 @@ function edit.mouse_pressed(State, x,y, mouse_button)
       if Drawing.in_drawing(line, x, y) then
         State.lines.current_drawing_index = line_index
         State.lines.current_drawing = line
-        Drawing.before = snapshot(line_index)
+        Drawing.before = snapshot(State, line_index)
         Drawing.mouse_pressed(State, line, x,y, mouse_button)
         break
       end
@@ -242,7 +242,7 @@ function edit.mouse_released(State, x,y, mouse_button)
     Drawing.mouse_released(State, x,y, mouse_button)
     schedule_save(State)
     if Drawing.before then
-      record_undo_event({before=Drawing.before, after=snapshot(State.lines.current_drawing_index)})
+      record_undo_event(State, {before=Drawing.before, after=snapshot(State, State.lines.current_drawing_index)})
       Drawing.before = nil
     end
   else
@@ -281,11 +281,11 @@ function edit.textinput(State, t)
     State.search_text = nil
     Text.search_next()
   elseif State.current_drawing_mode == 'name' then
-    local before = snapshot(State.lines.current_drawing_index)
+    local before = snapshot(State, State.lines.current_drawing_index)
     local drawing = State.lines.current_drawing
     local p = drawing.points[drawing.pending.target_point]
     p.name = p.name..t
-    record_undo_event({before=before, after=snapshot(State.lines.current_drawing_index)})
+    record_undo_event(State, {before=before, after=snapshot(State, State.lines.current_drawing_index)})
   else
     Text.textinput(State, t)
   end
@@ -340,7 +340,7 @@ function edit.keychord_pressed(State, chord, key)
     Text.redraw_all()
   elseif chord == 'C-z' then
     for _,line in ipairs(State.lines) do line.y = nil end  -- just in case we scroll
-    local event = undo_event()
+    local event = undo_event(State)
     if event then
       local src = event.before
       State.screen_top1 = deepcopy(src.screen_top)
@@ -352,7 +352,7 @@ function edit.keychord_pressed(State, chord, key)
     end
   elseif chord == 'C-y' then
     for _,line in ipairs(State.lines) do line.y = nil end  -- just in case we scroll
-    local event = redo_event()
+    local event = redo_event(State)
     if event then
       local src = event.after
       State.screen_top1 = deepcopy(src.screen_top)
@@ -381,7 +381,7 @@ function edit.keychord_pressed(State, chord, key)
     -- We don't have a good sense of when to scroll, so we'll be conservative
     -- and sometimes scroll when we didn't quite need to.
     local before_line = State.cursor1.line
-    local before = snapshot(before_line)
+    local before = snapshot(State, before_line)
     local clipboard_data = App.getClipboardText()
     for _,code in utf8.codes(clipboard_data) do
       local c = utf8.char(code)
@@ -395,15 +395,15 @@ function edit.keychord_pressed(State, chord, key)
       Text.snap_cursor_to_bottom_of_screen(State.margin_left, App.screen.height-State.margin_right)
     end
     schedule_save(State)
-    record_undo_event({before=before, after=snapshot(before_line, State.cursor1.line)})
+    record_undo_event(State, {before=before, after=snapshot(State, before_line, State.cursor1.line)})
   -- dispatch to drawing or text
   elseif App.mouse_down(1) or chord:sub(1,2) == 'C-' then
     -- DON'T reset line.y here
     local drawing_index, drawing = Drawing.current_drawing()
     if drawing_index then
-      local before = snapshot(drawing_index)
+      local before = snapshot(State, drawing_index)
       Drawing.keychord_pressed(State, chord)
-      record_undo_event({before=before, after=snapshot(drawing_index)})
+      record_undo_event(State, {before=before, after=snapshot(State, drawing_index)})
       schedule_save(State)
     end
   elseif chord == 'escape' and not App.mouse_down(1) then
@@ -417,18 +417,18 @@ function edit.keychord_pressed(State, chord, key)
       State.current_drawing_mode = State.previous_drawing_mode
       State.previous_drawing_mode = nil
     else
-      local before = snapshot(State.lines.current_drawing_index)
+      local before = snapshot(State, State.lines.current_drawing_index)
       local drawing = State.lines.current_drawing
       local p = drawing.points[drawing.pending.target_point]
       if chord == 'escape' then
         p.name = nil
-        record_undo_event({before=before, after=snapshot(State.lines.current_drawing_index)})
+        record_undo_event(State, {before=before, after=snapshot(State, State.lines.current_drawing_index)})
       elseif chord == 'backspace' then
         local len = utf8.len(p.name)
         local byte_offset = Text.offset(p.name, len-1)
         if len == 1 then byte_offset = 0 end
         p.name = string.sub(p.name, 1, byte_offset)
-        record_undo_event({before=before, after=snapshot(State.lines.current_drawing_index)})
+        record_undo_event(State, {before=before, after=snapshot(State, State.lines.current_drawing_index)})
       end
     end
     schedule_save(State)
diff --git a/select.lua b/select.lua
index dfa7f45..1b74858 100644
--- a/select.lua
+++ b/select.lua
@@ -110,9 +110,9 @@ end
 function Text.delete_selection(State, left, right)
   if State.selection1.line == nil then return end
   local minl,maxl = minmax(State.selection1.line, State.cursor1.line)
-  local before = snapshot(minl, maxl)
+  local before = snapshot(State, minl, maxl)
   Text.delete_selection_without_undo(State, left, right)
-  record_undo_event({before=before, after=snapshot(State.cursor1.line)})
+  record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
 end
 
 function Text.delete_selection_without_undo(State, left, right)
diff --git a/text.lua b/text.lua
index edab9f5..74cf2a6 100644
--- a/text.lua
+++ b/text.lua
@@ -137,7 +137,7 @@ end
 function Text.textinput(State, t)
   if App.mouse_down(1) then return end
   if App.ctrl_down() or App.alt_down() or App.cmd_down() then return end
-  local before = snapshot(State.cursor1.line)
+  local before = snapshot(State, State.cursor1.line)
 --?   print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
   Text.insert_at_cursor(State, t)
   if State.cursor_y >= App.screen.height - State.line_height then
@@ -145,7 +145,7 @@ function Text.textinput(State, t)
     Text.snap_cursor_to_bottom_of_screen(State.margin_left, App.screen.width-State.margin_right)
 --?     print('=>', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
   end
-  record_undo_event({before=before, after=snapshot(State.cursor1.line)})
+  record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
 end
 
 function Text.insert_at_cursor(State, t)
@@ -161,16 +161,16 @@ function Text.keychord_pressed(State, chord)
   --== shortcuts that mutate text
   if chord == 'return' then
     local before_line = State.cursor1.line
-    local before = snapshot(before_line)
+    local before = snapshot(State, before_line)
     Text.insert_return(State)
     State.selection1 = {}
     if (State.cursor_y + State.line_height) > App.screen.height then
       Text.snap_cursor_to_bottom_of_screen(State.margin_left, App.screen.width-State.margin_right)
     end
     schedule_save(State)
-    record_undo_event({before=before, after=snapshot(before_line, State.cursor1.line)})
+    record_undo_event(State, {before=before, after=snapshot(State, before_line, State.cursor1.line)})
   elseif chord == 'tab' then
-    local before = snapshot(State.cursor1.line)
+    local before = snapshot(State, State.cursor1.line)
 --?     print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
     Text.insert_at_cursor(State, '\t')
     if State.cursor_y >= App.screen.height - State.line_height then
@@ -179,7 +179,7 @@ function Text.keychord_pressed(State, chord)
 --?       print('=>', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
     end
     schedule_save(State)
-    record_undo_event({before=before, after=snapshot(State.cursor1.line)})
+    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
   elseif chord == 'backspace' then
     if State.selection1.line then
       Text.delete_selection(State, State.margin_left, App.screen.width-State.margin_right)
@@ -188,7 +188,7 @@ function Text.keychord_pressed(State, chord)
     end
     local before
     if State.cursor1.pos > 1 then
-      before = snapshot(State.cursor1.line)
+      before = snapshot(State, State.cursor1.line)
       local byte_start = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos-1)
       local byte_end = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
       if byte_start then
@@ -200,7 +200,7 @@ function Text.keychord_pressed(State, chord)
         State.cursor1.pos = State.cursor1.pos-1
       end
     elseif State.cursor1.line > 1 then
-      before = snapshot(State.cursor1.line-1, State.cursor1.line)
+      before = snapshot(State, State.cursor1.line-1, State.cursor1.line)
       if State.lines[State.cursor1.line-1].mode == 'drawing' then
         table.remove(State.lines, State.cursor1.line-1)
       else
@@ -220,7 +220,7 @@ function Text.keychord_pressed(State, chord)
     Text.clear_cache(State.lines[State.cursor1.line])
     assert(Text.le1(State.screen_top1, State.cursor1))
     schedule_save(State)
-    record_undo_event({before=before, after=snapshot(State.cursor1.line)})
+    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
   elseif chord == 'delete' then
     if State.selection1.line then
       Text.delete_selection(State, State.margin_left, App.screen.width-State.margin_right)
@@ -229,9 +229,9 @@ function Text.keychord_pressed(State, chord)
     end
     local before
     if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
-      before = snapshot(State.cursor1.line)
+      before = snapshot(State, State.cursor1.line)
     else
-      before = snapshot(State.cursor1.line, State.cursor1.line+1)
+      before = snapshot(State, State.cursor1.line, State.cursor1.line+1)
     end
     if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
       local byte_start = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
@@ -255,7 +255,7 @@ function Text.keychord_pressed(State, chord)
     end
     Text.clear_cache(State.lines[State.cursor1.line])
     schedule_save(State)
-    record_undo_event({before=before, after=snapshot(State.cursor1.line)})
+    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
   --== shortcuts that move the cursor
   elseif chord == 'left' then
     Text.left(State, State.margin_left, App.screen.width-State.margin_right)
diff --git a/undo.lua b/undo.lua
index 8e5491c..f56a348 100644
--- a/undo.lua
+++ b/undo.lua
@@ -6,52 +6,52 @@
 -- TODO: highlight stuff inserted by any undo/redo operation
 -- TODO: coalesce multiple similar operations
 
-function record_undo_event(data)
-  Editor_state.history[Editor_state.next_history] = data
-  Editor_state.next_history = Editor_state.next_history+1
-  for i=Editor_state.next_history,#Editor_state.history do
-    Editor_state.history[i] = nil
+function record_undo_event(State, data)
+  State.history[State.next_history] = data
+  State.next_history = State.next_history+1
+  for i=State.next_history,#State.history do
+    State.history[i] = nil
   end
 end
 
-function undo_event()
-  if Editor_state.next_history > 1 then
---?     print('moving to history', Editor_state.next_history-1)
-    Editor_state.next_history = Editor_state.next_history-1
-    local result = Editor_state.history[Editor_state.next_history]
+function undo_event(State)
+  if State.next_history > 1 then
+--?     print('moving to history', State.next_history-1)
+    State.next_history = State.next_history-1
+    local result = State.history[State.next_history]
     return result
   end
 end
 
-function redo_event()
-  if Editor_state.next_history <= #Editor_state.history then
---?     print('restoring history', Editor_state.next_history+1)
-    local result = Editor_state.history[Editor_state.next_history]
-    Editor_state.next_history = Editor_state.next_history+1
+function redo_event(State)
+  if State.next_history <= #State.history then
+--?     print('restoring history', State.next_history+1)
+    local result = State.history[State.next_history]
+    State.next_history = State.next_history+1
     return result
   end
 end
 
 -- Copy all relevant global state.
 -- Make copies of objects; the rest of the app may mutate them in place, but undo requires immutable histories.
-function snapshot(s,e)
+function snapshot(State, s,e)
   -- Snapshot everything by default, but subset if requested.
   assert(s)
   if e == nil then
     e = s
   end
-  assert(#Editor_state.lines > 0)
+  assert(#State.lines > 0)
   if s < 1 then s = 1 end
-  if s > #Editor_state.lines then s = #Editor_state.lines end
+  if s > #State.lines then s = #State.lines end
   if e < 1 then e = 1 end
-  if e > #Editor_state.lines then e = #Editor_state.lines end
+  if e > #State.lines then e = #State.lines end
   -- compare with App.initialize_globals
   local event = {
-    screen_top=deepcopy(Editor_state.screen_top1),
-    selection=deepcopy(Editor_state.selection1),
-    cursor=deepcopy(Editor_state.cursor1),
+    screen_top=deepcopy(State.screen_top1),
+    selection=deepcopy(State.selection1),
+    cursor=deepcopy(State.cursor1),
     current_drawing_mode=Drawing_mode,
-    previous_drawing_mode=Editor_state.previous_drawing_mode,
+    previous_drawing_mode=State.previous_drawing_mode,
     lines={},
     start_line=s,
     end_line=e,
@@ -59,7 +59,7 @@ function snapshot(s,e)
   }
   -- deep copy lines without cached stuff like text fragments
   for i=s,e do
-    local line = Editor_state.lines[i]
+    local line = State.lines[i]
     if line.mode == 'text' then
       table.insert(event.lines, {mode='text', data=line.data})
     elseif line.mode == 'drawing' then