stop caching starty

This is quite useful because I used to have a long list of places in
which to invalidate the cache.

12 files changed, 148 insertions, 107 deletions

diff --git a/app.lua b/app.lua
index 5e61d47..274f38d 100644
--- a/app.lua
+++ b/app.lua
@@ -131,7 +131,7 @@ function App.run_tests()
   end
   table.sort(sorted_names)
 --?   App.initialize_for_test() -- debug: run a single test at a time like these 2 lines
---?   test_pagedown_skips_drawings()
+--?   test_click_moves_cursor()
   for _,name in ipairs(sorted_names) do
     App.initialize_for_test()
 --?     print('=== '..name)
diff --git a/drawing.lua b/drawing.lua
index 246c7ae..92e3d5f 100644
--- a/drawing.lua
+++ b/drawing.lua
@@ -6,16 +6,15 @@ require 'drawing_tests'
 -- into 256 parts.
 function Drawing.draw(State, line_index, y)
   local line = State.lines[line_index]
-  local line_cache = State.line_cache[line_index]
-  line_cache.starty = y
   local pmx,pmy = App.mouse_x(), App.mouse_y()
-  if pmx < State.right and pmy > line_cache.starty and pmy < line_cache.starty+Drawing.pixels(line.h, State.width) then
+  local starty = Text.starty(State, line_index)
+  if pmx < State.right and pmy > starty and pmy < starty+Drawing.pixels(line.h, State.width) then
     App.color(Icon_color)
-    love.graphics.rectangle('line', State.left,line_cache.starty, State.width,Drawing.pixels(line.h, State.width))
+    love.graphics.rectangle('line', State.left,starty, State.width,Drawing.pixels(line.h, State.width))
     if icon[State.current_drawing_mode] then
-      icon[State.current_drawing_mode](State.right-22, line_cache.starty+4)
+      icon[State.current_drawing_mode](State.right-22, starty+4)
     else
-      icon[State.previous_drawing_mode](State.right-22, line_cache.starty+4)
+      icon[State.previous_drawing_mode](State.right-22, starty+4)
     end
 
     if App.mouse_down(1) and love.keyboard.isDown('h') then
@@ -30,7 +29,7 @@ function Drawing.draw(State, line_index, y)
   end
 
   local mx = Drawing.coord(pmx-State.left, State.width)
-  local my = Drawing.coord(pmy-line_cache.starty, State.width)
+  local my = Drawing.coord(pmy-starty, State.width)
 
   for _,shape in ipairs(line.shapes) do
     if geom.on_shape(mx,my, line, shape) then
@@ -38,11 +37,11 @@ function Drawing.draw(State, line_index, y)
     else
       App.color(Stroke_color)
     end
-    Drawing.draw_shape(line, shape, line_cache.starty, State.left,State.right)
+    Drawing.draw_shape(line, shape, starty, State.left,State.right)
   end
 
   local function px(x) return Drawing.pixels(x, State.width)+State.left end
-  local function py(y) return Drawing.pixels(y, State.width)+line_cache.starty end
+  local function py(y) return Drawing.pixels(y, State.width)+starty end
   for i,p in ipairs(line.points) do
     if p.deleted == nil then
       if Drawing.near(p, mx,my, State.width) then
@@ -71,7 +70,7 @@ function Drawing.draw(State, line_index, y)
     end
   end
   App.color(Current_stroke_color)
-  Drawing.draw_pending_shape(line, line_cache.starty, State.left,State.right)
+  Drawing.draw_pending_shape(line, starty, State.left,State.right)
 end
 
 function Drawing.draw_shape(drawing, shape, top, left,right)
@@ -209,17 +208,24 @@ function Drawing.draw_pending_shape(drawing, top, left,right)
   end
 end
 
-function Drawing.in_drawing(drawing, line_cache, x,y, left,right)
-  if line_cache.starty == nil then return false end  -- outside current page
+function Drawing.in_current_drawing(State, x,y, left,right)
+  return Drawing.in_drawing(State, State.lines.current_drawing_index, x,y, left,right)
+end
+
+function Drawing.in_drawing(State, line_index, x,y, left,right)
+  assert(State.lines[line_index].mode == 'drawing')
+  local starty = Text.starty(State, line_index)
+  if starty == nil then return false end  -- outside current page
+  local drawing = State.lines[line_index]
   local width = right-left
-  return y >= line_cache.starty and y < line_cache.starty + Drawing.pixels(drawing.h, width) and x >= left and x < right
+  return y >= starty and y < starty + Drawing.pixels(drawing.h, width) and x >= left and x < right
 end
 
 function Drawing.mouse_press(State, drawing_index, x,y, mouse_button)
   local drawing = State.lines[drawing_index]
-  local line_cache = State.line_cache[drawing_index]
+  local starty = Text.starty(State, drawing_index)
   local cx = Drawing.coord(x-State.left, State.width)
-  local cy = Drawing.coord(y-line_cache.starty, State.width)
+  local cy = Drawing.coord(y-starty, State.width)
   if State.current_drawing_mode == 'freehand' then
     drawing.pending = {mode=State.current_drawing_mode, points={{x=cx, y=cy}}}
   elseif State.current_drawing_mode == 'line' or State.current_drawing_mode == 'manhattan' then
@@ -244,8 +250,8 @@ end
 function Drawing.update(State)
   if State.lines.current_drawing == nil then return end
   local drawing = State.lines.current_drawing
-  local line_cache = State.line_cache[State.lines.current_drawing_index]
-  if line_cache.starty == nil then
+  local starty = Text.starty(State, State.lines.current_drawing_index)
+  if starty == nil then
     -- some event cleared starty just this frame
     -- draw in this frame will soon set starty
     -- just skip this frame
@@ -254,9 +260,9 @@ function Drawing.update(State)
   assert(drawing.mode == 'drawing', 'Drawing.update: line is not a drawing')
   local pmx, pmy = App.mouse_x(), App.mouse_y()
   local mx = Drawing.coord(pmx-State.left, State.width)
-  local my = Drawing.coord(pmy-line_cache.starty, State.width)
+  local my = Drawing.coord(pmy-starty, State.width)
   if App.mouse_down(1) then
-    if Drawing.in_drawing(drawing, line_cache, pmx,pmy, State.left,State.right) then
+    if Drawing.in_current_drawing(State, pmx,pmy, State.left,State.right) then
       if drawing.pending.mode == 'freehand' then
         table.insert(drawing.pending.points, {x=mx, y=my})
       elseif drawing.pending.mode == 'move' then
@@ -266,7 +272,7 @@ function Drawing.update(State)
       end
     end
   elseif State.current_drawing_mode == 'move' then
-    if Drawing.in_drawing(drawing, line_cache, pmx, pmy, State.left,State.right) then
+    if Drawing.in_current_drawing(State, pmx, pmy, State.left,State.right) then
       drawing.pending.target_point.x = mx
       drawing.pending.target_point.y = my
       Drawing.relax_constraints(drawing, drawing.pending.target_point_index)
@@ -304,7 +310,7 @@ function Drawing.mouse_release(State, x,y, mouse_button)
     end
   elseif State.lines.current_drawing then
     local drawing = State.lines.current_drawing
-    local line_cache = State.line_cache[State.lines.current_drawing_index]
+    local starty = Text.starty(State, State.lines.current_drawing_index)
     if drawing.pending then
       if drawing.pending.mode == nil then
         -- nothing pending
@@ -313,14 +319,14 @@ function Drawing.mouse_release(State, x,y, mouse_button)
         Drawing.smoothen(drawing.pending)
         table.insert(drawing.shapes, drawing.pending)
       elseif drawing.pending.mode == 'line' then
-        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
         if mx >= 0 and mx < 256 and my >= 0 and my < drawing.h then
           drawing.pending.p2 = Drawing.find_or_insert_point(drawing.points, mx,my, State.width)
           table.insert(drawing.shapes, drawing.pending)
         end
       elseif drawing.pending.mode == 'manhattan' then
         local p1 = drawing.points[drawing.pending.p1]
-        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
         if mx >= 0 and mx < 256 and my >= 0 and my < drawing.h then
           if math.abs(mx-p1.x) > math.abs(my-p1.y) then
             drawing.pending.p2 = Drawing.find_or_insert_point(drawing.points, mx, p1.y, State.width)
@@ -328,11 +334,11 @@ function Drawing.mouse_release(State, x,y, mouse_button)
             drawing.pending.p2 = Drawing.find_or_insert_point(drawing.points, p1.x, my, State.width)
           end
           local p2 = drawing.points[drawing.pending.p2]
-          App.mouse_move(State.left+Drawing.pixels(p2.x, State.width), line_cache.starty+Drawing.pixels(p2.y, State.width))
+          App.mouse_move(State.left+Drawing.pixels(p2.x, State.width), starty+Drawing.pixels(p2.y, State.width))
           table.insert(drawing.shapes, drawing.pending)
         end
       elseif drawing.pending.mode == 'polygon' then
-        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
         if mx >= 0 and mx < 256 and my >= 0 and my < drawing.h then
           table.insert(drawing.pending.vertices, Drawing.find_or_insert_point(drawing.points, mx,my, State.width))
           table.insert(drawing.shapes, drawing.pending)
@@ -340,7 +346,7 @@ function Drawing.mouse_release(State, x,y, mouse_button)
       elseif drawing.pending.mode == 'rectangle' then
         assert(#drawing.pending.vertices <= 2, 'Drawing.mouse_release: rectangle has too many pending vertices')
         if #drawing.pending.vertices == 2 then
-          local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+          local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
           if mx >= 0 and mx < 256 and my >= 0 and my < drawing.h then
             local first = drawing.points[drawing.pending.vertices[1]]
             local second = drawing.points[drawing.pending.vertices[2]]
@@ -355,7 +361,7 @@ function Drawing.mouse_release(State, x,y, mouse_button)
       elseif drawing.pending.mode == 'square' then
         assert(#drawing.pending.vertices <= 2, 'Drawing.mouse_release: square has too many pending vertices')
         if #drawing.pending.vertices == 2 then
-          local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+          local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
           if mx >= 0 and mx < 256 and my >= 0 and my < drawing.h then
             local first = drawing.points[drawing.pending.vertices[1]]
             local second = drawing.points[drawing.pending.vertices[2]]
@@ -366,14 +372,14 @@ function Drawing.mouse_release(State, x,y, mouse_button)
           end
         end
       elseif drawing.pending.mode == 'circle' then
-        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
         if mx >= 0 and mx < 256 and my >= 0 and my < drawing.h then
           local center = drawing.points[drawing.pending.center]
           drawing.pending.radius = round(geom.dist(center.x,center.y, mx,my))
           table.insert(drawing.shapes, drawing.pending)
         end
       elseif drawing.pending.mode == 'arc' then
-        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
         if mx >= 0 and mx < 256 and my >= 0 and my < drawing.h then
           local center = drawing.points[drawing.pending.center]
           drawing.pending.end_angle = geom.angle_with_hint(center.x,center.y, mx,my, drawing.pending.end_angle)
@@ -477,13 +483,15 @@ function Drawing.keychord_press(State, chord)
     end
     drawing.pending.mode = 'square'
   elseif App.mouse_down(1) and chord == 'p' and State.current_drawing_mode == 'polygon' then
-    local _,drawing,line_cache = Drawing.current_drawing(State)
-    local mx,my = Drawing.coord(App.mouse_x()-State.left, State.width), Drawing.coord(App.mouse_y()-line_cache.starty, State.width)
+    local drawing_index,drawing = Drawing.current_drawing(State)
+    local starty = Text.starty(State, drawing_index)
+    local mx,my = Drawing.coord(App.mouse_x()-State.left, State.width), Drawing.coord(App.mouse_y()-starty, State.width)
     local j = Drawing.find_or_insert_point(drawing.points, mx,my, State.width)
     table.insert(drawing.pending.vertices, j)
   elseif App.mouse_down(1) and chord == 'p' and (State.current_drawing_mode == 'rectangle' or State.current_drawing_mode == 'square') then
-    local _,drawing,line_cache = Drawing.current_drawing(State)
-    local mx,my = Drawing.coord(App.mouse_x()-State.left, State.width), Drawing.coord(App.mouse_y()-line_cache.starty, State.width)
+    local drawing_index,drawing = Drawing.current_drawing(State)
+    local starty = Text.starty(State, drawing_index)
+    local mx,my = Drawing.coord(App.mouse_x()-State.left, State.width), Drawing.coord(App.mouse_y()-starty, State.width)
     local j = Drawing.find_or_insert_point(drawing.points, mx,my, State.width)
     while #drawing.pending.vertices >= 2 do
       table.remove(drawing.pending.vertices)
@@ -492,9 +500,10 @@ function Drawing.keychord_press(State, chord)
   elseif chord == 'C-o' and not App.mouse_down(1) then
     State.current_drawing_mode = 'circle'
   elseif App.mouse_down(1) and chord == 'a' and State.current_drawing_mode == 'circle' then
-    local _,drawing,line_cache = Drawing.current_drawing(State)
+    local drawing_index,drawing = Drawing.current_drawing(State)
+    local starty = Text.starty(State, drawing_index)
     drawing.pending.mode = 'arc'
-    local mx,my = Drawing.coord(App.mouse_x()-State.left, State.width), Drawing.coord(App.mouse_y()-line_cache.starty, State.width)
+    local mx,my = Drawing.coord(App.mouse_x()-State.left, State.width), Drawing.coord(App.mouse_y()-starty, State.width)
     local center = drawing.points[drawing.pending.center]
     drawing.pending.radius = round(geom.dist(center.x,center.y, mx,my))
     drawing.pending.start_angle = geom.angle(center.x,center.y, mx,my)
@@ -510,7 +519,7 @@ function Drawing.keychord_press(State, chord)
     end
     drawing.pending.mode = 'circle'
   elseif chord == 'C-u' and not App.mouse_down(1) then
-    local drawing_index,drawing,line_cache,i,p = Drawing.select_point_at_mouse(State)
+    local drawing_index,drawing,_,i,p = Drawing.select_point_at_mouse(State)
     if drawing then
       if State.previous_drawing_mode == nil then
         State.previous_drawing_mode = State.current_drawing_mode
@@ -521,7 +530,7 @@ function Drawing.keychord_press(State, chord)
       State.lines.current_drawing = drawing
     end
   elseif chord == 'C-n' and not App.mouse_down(1) then
-    local drawing_index,drawing,line_cache,point_index,p = Drawing.select_point_at_mouse(State)
+    local drawing_index,drawing,_,point_index,p = Drawing.select_point_at_mouse(State)
     if drawing then
       if State.previous_drawing_mode == nil then
         -- don't clobber
@@ -619,9 +628,8 @@ function Drawing.current_drawing(State)
   local x, y = App.mouse_x(), App.mouse_y()
   for drawing_index,drawing in ipairs(State.lines) do
     if drawing.mode == 'drawing' then
-      local line_cache = State.line_cache[drawing_index]
-      if Drawing.in_drawing(drawing, line_cache, x,y, State.left,State.right) then
-        return drawing_index,drawing,line_cache
+      if Drawing.in_drawing(State, drawing_index, x,y, State.left,State.right) then
+        return drawing_index,drawing
       end
     end
   end
@@ -632,12 +640,12 @@ function Drawing.select_shape_at_mouse(State)
   for drawing_index,drawing in ipairs(State.lines) do
     if drawing.mode == 'drawing' then
       local x, y = App.mouse_x(), App.mouse_y()
-      local line_cache = State.line_cache[drawing_index]
-      if Drawing.in_drawing(drawing, line_cache, x,y, State.left,State.right) then
-        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+      local starty = Text.starty(State, drawing_index)
+      if Drawing.in_drawing(State, drawing_index, x,y, State.left,State.right) then
+        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
         for i,shape in ipairs(drawing.shapes) do
           if geom.on_shape(mx,my, drawing, shape) then
-            return drawing,line_cache,i,shape
+            return drawing,starty,i,shape
           end
         end
       end
@@ -649,12 +657,12 @@ function Drawing.select_point_at_mouse(State)
   for drawing_index,drawing in ipairs(State.lines) do
     if drawing.mode == 'drawing' then
       local x, y = App.mouse_x(), App.mouse_y()
-      local line_cache = State.line_cache[drawing_index]
-      if Drawing.in_drawing(drawing, line_cache, x,y, State.left,State.right) then
-        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-line_cache.starty, State.width)
+      local starty = Text.starty(State, drawing_index)
+      if Drawing.in_drawing(State, drawing_index, x,y, State.left,State.right) then
+        local mx,my = Drawing.coord(x-State.left, State.width), Drawing.coord(y-starty, State.width)
         for i,point in ipairs(drawing.points) do
           if Drawing.near(point, mx,my, State.width) then
-            return drawing_index,drawing,line_cache,i,point
+            return drawing_index,drawing,starty,i,point
           end
         end
       end
@@ -666,8 +674,7 @@ function Drawing.select_drawing_at_mouse(State)
   for drawing_index,drawing in ipairs(State.lines) do
     if drawing.mode == 'drawing' then
       local x, y = App.mouse_x(), App.mouse_y()
-      local line_cache = State.line_cache[drawing_index]
-      if Drawing.in_drawing(drawing, line_cache, x,y, State.left,State.right) then
+      if Drawing.in_drawing(State, drawing_index, x,y, State.left,State.right) then
         return drawing
       end
     end
diff --git a/drawing_tests.lua b/drawing_tests.lua
index 64188df..3484436 100644
--- a/drawing_tests.lua
+++ b/drawing_tests.lua
@@ -32,7 +32,7 @@ function test_draw_line()
   edit.draw(Editor_state)
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- draw a line
@@ -77,7 +77,7 @@ function test_draw_horizontal_line()
   edit.draw(Editor_state)
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- draw a line that is more horizontal than vertical
@@ -105,7 +105,7 @@ function test_draw_circle()
   edit.draw(Editor_state)
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- draw a circle
@@ -134,7 +134,7 @@ function test_cancel_stroke()
   edit.draw(Editor_state)
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- start drawing a line
@@ -172,7 +172,7 @@ function test_draw_circle_mid_stroke()
   edit.draw(Editor_state)
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- draw a circle
@@ -200,7 +200,7 @@ function test_draw_arc()
   edit.draw(Editor_state)
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- draw an arc
@@ -231,7 +231,7 @@ function test_draw_polygon()
   check_eq(Editor_state.current_drawing_mode, 'line', 'baseline/drawing_mode')
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- first point
@@ -269,7 +269,7 @@ function test_draw_rectangle()
   check_eq(Editor_state.current_drawing_mode, 'line', 'baseline/drawing_mode')
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- first point
@@ -313,7 +313,7 @@ function test_draw_rectangle_intermediate()
   check_eq(Editor_state.current_drawing_mode, 'line', 'baseline/drawing_mode')
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- first point
@@ -349,7 +349,7 @@ function test_draw_square()
   check_eq(Editor_state.current_drawing_mode, 'line', 'baseline/drawing_mode')
   check_eq(#Editor_state.lines, 2, 'baseline/#lines')
   check_eq(Editor_state.lines[1].mode, 'drawing', 'baseline/mode')
-  check_eq(Editor_state.line_cache[1].starty, Editor_state.top+Drawing_padding_top, 'baseline/y')
+  check_eq(Text.starty(Editor_state, 1), Editor_state.top+Drawing_padding_top, 'baseline/y')
   check_eq(Editor_state.lines[1].h, 128, 'baseline/y')
   check_eq(#Editor_state.lines[1].shapes, 0, 'baseline/#shapes')
   -- first point
diff --git a/edit.lua b/edit.lua
index 5a2ab28..7154a7d 100644
--- a/edit.lua
+++ b/edit.lua
@@ -31,7 +31,6 @@ function edit.initialize_state(top, left, right, font, font_height, line_height)
     --    string data,
     -- a drawing is a table with:
     --    mode = 'drawing'
-    --    a (y) coord in pixels (updated while painting screen),
     --    a (h)eight,
     --    an array of points, and
     --    an array of shapes
@@ -52,7 +51,6 @@ function edit.initialize_state(top, left, right, font, font_height, line_height)
 
     -- rendering wrapped text lines needs some additional short-lived data per line:
     --   startpos, the index of data the line starts rendering from, can only be >1 for topmost line on screen
-    --   starty, the y coord in pixels the line starts rendering from
     --   fragments: snippets of the line guaranteed to not straddle screen lines
     --   screen_line_starting_pos: optional array of grapheme indices if it wraps over more than one screen line
     line_cache = {},
@@ -184,7 +182,6 @@ function edit.draw(State)
                        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={}})
                        table.insert(State.line_cache, line_index, {})
-                       for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end
                        if State.cursor1.line >= line_index then
                          State.cursor1.line = State.cursor1.line+1
                        end
@@ -276,8 +273,7 @@ function edit.mouse_press(State, x,y, mouse_button)
         return
       end
     elseif line.mode == 'drawing' then
-      local line_cache = State.line_cache[line_index]
-      if Drawing.in_drawing(line, line_cache, x, y, State.left,State.right) then
+      if Drawing.in_drawing(State, line_index, x, y, State.left,State.right) then
         State.lines.current_drawing_index = line_index
         State.lines.current_drawing = line
         Drawing.before = snapshot(State, line_index)
@@ -395,7 +391,6 @@ function edit.keychord_press(State, chord, key)
     Text.delete_selection(State, State.left, State.right)
   end
   if State.search_term then
-    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
     if chord == 'escape' then
       State.search_term = nil
       State.cursor1 = State.search_backup.cursor
@@ -500,7 +495,6 @@ function edit.keychord_press(State, chord, key)
     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_cache.starty here
     local drawing_index, drawing = Drawing.current_drawing(State)
     if drawing_index then
       local before = snapshot(State, drawing_index)
@@ -537,7 +531,6 @@ function edit.keychord_press(State, chord, key)
     end
     schedule_save(State)
   else
-    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
     Text.keychord_press(State, chord)
   end
 end
diff --git a/help.lua b/help.lua
index 6f8633b..cc7a0c9 100644
--- a/help.lua
+++ b/help.lua
@@ -1,8 +1,8 @@
 function draw_help_without_mouse_pressed(State, drawing_index)
   local drawing = State.lines[drawing_index]
-  local line_cache = State.line_cache[drawing_index]
+  local starty = Text.starty(State, drawing_index)
   App.color(Help_color)
-  local y = line_cache.starty+10
+  local y = starty+10
   love.graphics.print("Things you can do:", State.left+30,y)
   y = y + State.line_height
   love.graphics.print("* Press the mouse button to start drawing a "..current_shape(State), State.left+30,y)
@@ -48,14 +48,14 @@ function draw_help_without_mouse_pressed(State, drawing_index)
   love.graphics.print("Press 'esc' now to hide this message", State.left+30,y)
   y = y + State.line_height
   App.color(Help_background_color)
-  love.graphics.rectangle('fill', State.left,line_cache.starty, State.width, math.max(Drawing.pixels(drawing.h, State.width),y-line_cache.starty))
+  love.graphics.rectangle('fill', State.left,starty, State.width, math.max(Drawing.pixels(drawing.h, State.width),y-starty))
 end
 
 function draw_help_with_mouse_pressed(State, drawing_index)
   local drawing = State.lines[drawing_index]
-  local line_cache = State.line_cache[drawing_index]
+  local starty = Text.starty(State, drawing_index)
   App.color(Help_color)
-  local y = line_cache.starty+10
+  local y = starty+10
   love.graphics.print("You're currently drawing a "..current_shape(State, drawing.pending), State.left+30,y)
   y = y + State.line_height
   love.graphics.print('Things you can do now:', State.left+30,y)
@@ -129,7 +129,7 @@ function draw_help_with_mouse_pressed(State, drawing_index)
     y = y + State.line_height
   end
   App.color(Help_background_color)
-  love.graphics.rectangle('fill', State.left,line_cache.starty, State.width, math.max(Drawing.pixels(drawing.h, State.width),y-line_cache.starty))
+  love.graphics.rectangle('fill', State.left,starty, State.width, math.max(Drawing.pixels(drawing.h, State.width),y-starty))
 end
 
 function current_shape(State, shape)
diff --git a/select.lua b/select.lua
index 78d18db..b67dd16 100644
--- a/select.lua
+++ b/select.lua
@@ -69,7 +69,7 @@ end
 
 function Text.mouse_pos(State)
   local x,y = App.mouse_x(), App.mouse_y()
-  if y < State.line_cache[State.screen_top1.line].starty then
+  if y < State.top then
     return State.screen_top1.line, State.screen_top1.pos
   end
   for line_index,line in ipairs(State.lines) do
diff --git a/source.lua b/source.lua
index 439efa3..d24957c 100644
--- a/source.lua
+++ b/source.lua
@@ -307,7 +307,6 @@ function source.mouse_press(x,y, mouse_button)
       return
     end
     log_browser.mouse_press(Log_browser_state, x,y, mouse_button)
-    for _,line_cache in ipairs(Editor_state.line_cache) do line_cache.starty = nil end  -- just in case we scroll
   end
 end
 
diff --git a/source_edit.lua b/source_edit.lua
index 64c8980..5351857 100644
--- a/source_edit.lua
+++ b/source_edit.lua
@@ -33,7 +33,6 @@ function edit.initialize_state(top, left, right, font, font_height, line_height)
     --    string data,
     -- a drawing is a table with:
     --    mode = 'drawing'
-    --    a (y) coord in pixels (updated while painting screen),
     --    a (h)eight,
     --    an array of points, and
     --    an array of shapes
@@ -54,7 +53,6 @@ function edit.initialize_state(top, left, right, font, font_height, line_height)
 
     -- rendering wrapped text lines needs some additional short-lived data per line:
     --   startpos, the index of data the line starts rendering from, can only be >1 for topmost line on screen
-    --   starty, the y coord in pixels the line starts rendering from
     --   fragments: snippets of the line guaranteed to not straddle screen lines
     --   screen_line_starting_pos: optional array of grapheme indices if it wraps over more than one screen line
     line_cache = {},
@@ -189,7 +187,6 @@ function edit.draw(State, hide_cursor, show_line_numbers)
                        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={}})
                        table.insert(State.line_cache, line_index, {})
-                       for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end
                        if State.cursor1.line >= line_index then
                          State.cursor1.line = State.cursor1.line+1
                        end
@@ -280,8 +277,7 @@ function edit.mouse_press(State, x,y, mouse_button)
         return
       end
     elseif line.mode == 'drawing' then
-      local line_cache = State.line_cache[line_index]
-      if Drawing.in_drawing(line, line_cache, x, y, State.left,State.right) then
+      if Drawing.in_drawing(State, line_index, x, y, State.left,State.right) then
         State.lines.current_drawing_index = line_index
         State.lines.current_drawing = line
         Drawing.before = snapshot(State, line_index)
@@ -399,7 +395,6 @@ function edit.keychord_press(State, chord, key)
     Text.delete_selection(State, State.left, State.right)
   end
   if State.search_term then
-    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
     if chord == 'escape' then
       State.search_term = nil
       State.cursor1 = State.search_backup.cursor
@@ -504,7 +499,6 @@ function edit.keychord_press(State, chord, key)
     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_cache.starty here
     local drawing_index, drawing = Drawing.current_drawing(State)
     if drawing_index then
       local before = snapshot(State, drawing_index)
@@ -541,7 +535,6 @@ function edit.keychord_press(State, chord, key)
     end
     schedule_save(State)
   else
-    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
     Text.keychord_press(State, chord)
   end
 end
diff --git a/source_text.lua b/source_text.lua
index 0fb1147..d2c68c2 100644
--- a/source_text.lua
+++ b/source_text.lua
@@ -6,7 +6,6 @@ Text = {}
 function Text.draw(State, line_index, y, startpos, hide_cursor, show_line_numbers)
   local line = State.lines[line_index]
   local line_cache = State.line_cache[line_index]
-  line_cache.starty = y
   line_cache.startpos = startpos
   -- wrap long lines
   Text.populate_screen_line_starting_pos(State, line_index)
@@ -431,6 +430,28 @@ function Text.pageup(State)
   Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
 end
 
+-- return the top y coordinate of a given line_index,
+-- or nil if no part of it is on screen
+function Text.starty(State, line_index)
+  -- duplicate some logic from love.draw
+  -- does not modify State (except to populate line_cache)
+  if line_index < State.screen_top1.line then return end
+  local loc2 = Text.to2(State, State.screen_top1)
+  local y = State.top
+  while true do
+    if loc2.line == line_index then return y end
+    if State.lines[loc2.line].mode == 'text' then
+      y = y + State.line_height
+    elseif State.lines[loc2.line].mode == 'drawing' then
+      y = y + Drawing_padding_height + Drawing.pixels(State.lines[loc2.line].h, State.width)
+    end
+    if y + State.line_height > App.screen.height then break end
+    local next_loc2 = Text.next_screen_line(State, loc2)
+    if Text.eq2(next_loc2, loc2) then break end  -- end of file
+    loc2 = next_loc2
+  end
+end
+
 function Text.previous_screen_top1(State)
   -- duplicate some logic from love.draw
   -- does not modify State (except to populate line_cache)
@@ -811,19 +832,21 @@ end
 function Text.in_line(State, line_index, x,y)
   local line = State.lines[line_index]
   local line_cache = State.line_cache[line_index]
-  if line_cache.starty == nil then return false end  -- outside current page
-  if y < line_cache.starty then return false end
+  local starty = Text.starty(State, line_index)
+  if starty == nil then return false end  -- outside current page
+  if y < starty then return false end
   Text.populate_screen_line_starting_pos(State, line_index)
-  return y < line_cache.starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)
+  return y < starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)
 end
 
 -- convert mx,my in pixels to schema-1 coordinates
 function Text.to_pos_on_line(State, line_index, mx, my)
   local line = State.lines[line_index]
   local line_cache = State.line_cache[line_index]
-  assert(my >= line_cache.starty, 'failed to map y pixel to line')
+  local starty = Text.starty(State, line_index)
+  assert(my >= starty, 'failed to map y pixel to line')
   -- duplicate some logic from Text.draw
-  local y = line_cache.starty
+  local y = starty
   local start_screen_line_index = Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos)
   for screen_line_index = start_screen_line_index,#line_cache.screen_line_starting_pos do
     local screen_line_starting_pos = line_cache.screen_line_starting_pos[screen_line_index]
diff --git a/source_text_tests.lua b/source_text_tests.lua
index c17842a..ce9cf3c 100644
--- a/source_text_tests.lua
+++ b/source_text_tests.lua
@@ -255,7 +255,7 @@ function test_click_moves_cursor()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
   check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
@@ -812,7 +812,7 @@ function test_select_text_using_mouse()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   -- press and hold on first location
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   -- drag and release somewhere else
@@ -831,7 +831,7 @@ function test_select_text_using_mouse_starting_above_text()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   -- press mouse above first line of text
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,5, 1)
   check(Editor_state.selection1.line ~= nil, 'selection:line-not-nil')
@@ -890,7 +890,7 @@ function test_select_text_using_mouse_and_shift()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   -- click on first location
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
@@ -914,7 +914,7 @@ function test_select_text_repeatedly_using_mouse_and_shift()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   -- click on first location
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
diff --git a/text.lua b/text.lua
index f203950..c897f0b 100644
--- a/text.lua
+++ b/text.lua
@@ -7,7 +7,6 @@ function Text.draw(State, line_index, y, startpos)
 --?   print('text.draw', line_index, y)
   local line = State.lines[line_index]
   local line_cache = State.line_cache[line_index]
-  line_cache.starty = y
   line_cache.startpos = startpos
   -- wrap long lines
   Text.populate_screen_line_starting_pos(State, line_index)
@@ -357,6 +356,31 @@ function Text.pageup(State)
   Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
 end
 
+-- return the top y coordinate of a given line_index,
+-- or nil if no part of it is on screen
+function Text.starty(State, line_index)
+  -- duplicate some logic from love.draw
+  -- does not modify State (except to populate line_cache)
+  if line_index < State.screen_top1.line then return end
+  local loc2 = Text.to2(State, State.screen_top1)
+  local y = State.top
+  while true do
+    if State.lines[loc2.line].mode == 'drawing' then
+      y = y + Drawing_padding_top
+    end
+    if loc2.line == line_index then return y end
+    if State.lines[loc2.line].mode == 'text' then
+      y = y + State.line_height
+    elseif State.lines[loc2.line].mode == 'drawing' then
+      y = y + Drawing.pixels(State.lines[loc2.line].h, State.width) + Drawing_padding_bottom
+    end
+    if y + State.line_height > App.screen.height then break end
+    local next_loc2 = Text.next_screen_line(State, loc2)
+    if Text.eq2(next_loc2, loc2) then break end  -- end of file
+    loc2 = next_loc2
+  end
+end
+
 function Text.previous_screen_top1(State)
   -- duplicate some logic from love.draw
   -- does not modify State (except to populate line_cache)
@@ -737,19 +761,21 @@ end
 function Text.in_line(State, line_index, x,y)
   local line = State.lines[line_index]
   local line_cache = State.line_cache[line_index]
-  if line_cache.starty == nil then return false end  -- outside current page
-  if y < line_cache.starty then return false end
+  local starty = Text.starty(State, line_index)
+  if starty == nil then return false end  -- outside current page
+  if y < starty then return false end
   Text.populate_screen_line_starting_pos(State, line_index)
-  return y < line_cache.starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)
+  return y < starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)
 end
 
 -- convert mx,my in pixels to schema-1 coordinates
 function Text.to_pos_on_line(State, line_index, mx, my)
   local line = State.lines[line_index]
   local line_cache = State.line_cache[line_index]
-  assert(my >= line_cache.starty, 'failed to map y pixel to line')
+  local starty = Text.starty(State, line_index)
+  assert(my >= starty, 'failed to map y pixel to line')
   -- duplicate some logic from Text.draw
-  local y = line_cache.starty
+  local y = starty
   local start_screen_line_index = Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos)
   for screen_line_index = start_screen_line_index,#line_cache.screen_line_starting_pos do
     local screen_line_starting_pos = line_cache.screen_line_starting_pos[screen_line_index]
diff --git a/text_tests.lua b/text_tests.lua
index 40320b1..9e42088 100644
--- a/text_tests.lua
+++ b/text_tests.lua
@@ -255,7 +255,7 @@ function test_click_moves_cursor()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line Editor_state.line_cache
   edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   check_eq(Editor_state.cursor1.line, 1, 'cursor:line')
   check_eq(Editor_state.cursor1.pos, 2, 'cursor:pos')
@@ -812,7 +812,7 @@ function test_select_text_using_mouse()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line Editor_state.line_cache
   -- press and hold on first location
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   -- drag and release somewhere else
@@ -831,7 +831,7 @@ function test_select_text_using_mouse_starting_above_text()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   -- press mouse above first line of text
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,5, 1)
   check(Editor_state.selection1.line ~= nil, 'selection:line-not-nil')
@@ -890,7 +890,7 @@ function test_select_text_using_mouse_and_shift()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   -- click on first location
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
@@ -914,7 +914,7 @@ function test_select_text_repeatedly_using_mouse_and_shift()
   Editor_state.cursor1 = {line=1, pos=1}
   Editor_state.screen_top1 = {line=1, pos=1}
   Editor_state.selection1 = {}
-  edit.draw(Editor_state)  -- populate line_cache.starty for each line Editor_state.line_cache
+  edit.draw(Editor_state)  -- populate line_cache.startpos for each line
   -- click on first location
   edit.run_after_mouse_press(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)
   edit.run_after_mouse_release(Editor_state, Editor_state.left+8,Editor_state.top+5, 1)