Give up on drawing partial drawings at top of screen

There are still open questions with that:
- say there's a partial drawing up top. Do we want to support drawing on
  it? It would be jarring for it to move right as you click on it. But
  might also not be a great experience to only see part of it.

- the current problem with snapping cursor to bottom is that I only want
  to include whole screen lines in that particular call to edit.up.

  On the other hand, drawings were supporting partial screen lines,
  which added a second layer of complexity to it. Now there's at least
  only one problem.

- all my basic move operations were always maintaining yoff in drawings.
  It's meaningless and ignored in cursor for the most part. But if I
  ever copy screen_top from cursor I have to remember to reset yoff. Now
  there's one less thing to remember.

edit.lua

@@ -62,7 +62,7 @@ function new_editor(top, left, right, bottom, font, font_height, line_height)  -
     cursor = nil,  -- location where editing will occur
     -- Valid location values:
     --   {mode='text', line=, pos=}
-    --   {mode='drawing', line=, yoff=}
+    --   {mode='drawing', line=}
 
     selection1 = {},
     -- some extra state to compute selection between mouse press and release
@@ -94,8 +94,8 @@ function edit.scroll_to_top(Editor)
     Editor.screen_top = {mode='text', line=1, pos=1}
     Editor.cursor = {mode='text', line=1, pos=1}
   else
-    Editor.screen_top = {mode='drawing', line=1, yoff=0}
-    Editor.cursor = {mode='drawing', line=1, yoff=0}
+    Editor.screen_top = {mode='drawing', line=1}
+    Editor.cursor = {mode='drawing', line=1}
   end
 end
 
@@ -159,7 +159,7 @@ function edit.draw(Editor)
           onpress1 = function()
                        Editor.drawing_before = snapshot(Editor, line_index-1, line_index)
                        table.insert(Editor.lines, line_index, {mode='drawing', y=y, h=256/2, points={}, shapes={}, pending={}})
-                       Editor.cursor = {mode='drawing', line=line_index, yoff=0}
+                       Editor.cursor = {mode='drawing', line=line_index}
                        schedule_save(Editor)
                        record_undo_event(Editor, {before=Editor.drawing_before, after=snapshot(Editor, line_index-1, line_index+1)})
                      end,
@@ -196,13 +196,9 @@ function edit.draw(Editor)
       do_it(x,y, 0, line_index, utf8.len(line.data)+1, '')
       y = y + Editor.line_height
     elseif line.mode == 'drawing' then
-      local yoff = 0
-      if line_index == Editor.screen_top.line then
-        yoff = Editor.screen_top.yoff or 0
-      end
       local h = Drawing_padding_height + Drawing.pixels(line.h, Editor.width)
-      Drawing.draw(Editor, line_index, y+Drawing_padding_top-yoff)
-      y = y + h - yoff
+      Drawing.draw(Editor, line_index, y+Drawing_padding_top)
+      y = y + h
     else
       assert(false, ('unknown line mode %s'):format(line.mode))
     end

move.lua

@@ -5,9 +5,8 @@
 -- (pos counts in utf8 codepoints starting from 1)
 --
 -- locations within drawings look like this:
---   {mode='drawing', line=, yoff=}
--- (yoff is only meaningful for the very top-most screen line drawn on screen
--- when we need to start drawing partway down)
+--   {mode='drawing', line=}
+-- (drawing lines are atomic as far as the cursor is concerned)
 --
 -- all movements are built primarily using the following primitives, defined
 -- further down:
@@ -106,17 +105,11 @@ end  -- 0-1 scan
 
 function Text.pageup(Editor)
   Editor.screen_top = edit.up(Editor, Editor.screen_top, Editor.bottom - Editor.top - Editor.line_height) -- scan
-  if Editor.screen_top.mode == 'drawing' then
-    Editor.screen_top.yoff = 0
-  end
   Editor.cursor = deepcopy(Editor.screen_top)
 end  -- 1 scan
 
 function Text.pagedown(Editor)
   Editor.screen_top = edit.down(Editor, Editor.screen_top, Editor.bottom - Editor.top - Editor.line_height)  -- scan
-  if Editor.screen_top.mode == 'drawing' then
-    Editor.screen_top.yoff = 0
-  end
   Editor.cursor = deepcopy(Editor.screen_top)
 end  -- 1 scan
 
@@ -262,14 +255,9 @@ function edit.to_loc(Editor, mx,my)
       y = y + Editor.line_height
     else
       -- drawing
-      local yoff = 0
-      if line_index == Editor.screen_top.line then
-        assert(Editor.screen_top.mode == 'drawing')
-        yoff = Editor.screen_top.yoff or 0
-      end
-      local h = Drawing_padding_height + Drawing.pixels(line.h, Editor.width) - yoff
+      local h = Drawing_padding_height + Drawing.pixels(line.h, Editor.width)
       if my < y+h then
-        return {mode='drawing', line=line_index, yoff=yoff}
+        return {mode='drawing', line=line_index}
       end
       y = y + h
     end
@@ -326,11 +314,7 @@ function edit.to_coord(Editor, loc)  -- scans
       if loc.mode == 'drawing' and loc.line == line_index then
         return x, y
       end
-      local yoff = 0
-      if line_index == Editor.screen_top.line then
-        yoff = Editor.screen_top.yoff or 0
-      end
-      y = y + Drawing.height(Editor, line) - yoff
+      y = y + Drawing.height(Editor, line)
     else
       assert(false, ('unknown line mode %s'):format(line.mode))
     end
@@ -357,17 +341,11 @@ function edit.down(Editor, loc, dy)  -- scans
         y = y + Editor.line_height
       end
     elseif line.mode == 'drawing' then
-      local yoff = 0
-      if line_index == loc.line then
-        -- yoff matters only when loc is screen_top
-        assert(loc.mode == 'drawing')
-        yoff = loc.yoff or 0
-      end
       local h = Drawing.height(Editor, line)
-      if y + h - yoff >= dy then
-        return {mode='drawing', line=line_index, yoff=dy-y}
+      if y + h >= dy then
+        return {mode='drawing', line=line_index}
       end
-      y = y + h - yoff
+      y = y + h
     else
       assert(false, ('unknown line mode %s'):format(line.mode))
     end
@@ -401,13 +379,8 @@ function edit.up(Editor, loc, dy)  -- scans
       end
     elseif line.mode == 'drawing' then
       local h = Drawing.height(Editor, line)
-      if line_index == loc.line then
-        assert(loc.mode == 'drawing')
-        -- _only_ when loc is screen_top, yoff bounds how much height we have to scan up within this drawing
-        h = loc.yoff or 0
-      end
       if y + h >= dy then
-        return {mode='drawing', line=line_index, yoff=dy-y}
+        return {mode='drawing', line=line_index}
       end
       y = y + h
     else
@@ -425,7 +398,7 @@ function edit.top(Editor)
   if Editor.lines[1].mode == 'text' then
     return {mode='text', line=1, pos=1}
   else
-    return {mode='drawing', line=1, yoff=0}
+    return {mode='drawing', line=1}
   end
 end
 
@@ -543,7 +516,7 @@ function Drawing.height(Editor, line)
 end
 
 function edit.eq(a, b)
-  return a.mode == b.mode and a.line == b.line and --[[just for text mode]] a.pos == b.pos  -- ignore yoff
+  return a.mode == b.mode and a.line == b.line and --[[just for text mode]] a.pos == b.pos
 end
 
 function edit.lt(a, b)

text.lua

@@ -101,7 +101,7 @@ function Text.keychord_press(Editor, chord)
       if Editor.lines[Editor.cursor.line].mode == 'text' then
         Editor.cursor = {mode='text', line=Editor.cursor.line, pos=1}
       else
-        Editor.cursor = {mode='drawing', line=Editor.cursor.line, yoff=0}
+        Editor.cursor = {mode='drawing', line=Editor.cursor.line}
       end
       -- no need to scroll, but screen_top may have switched mode
       if Editor.screen_top.line == Editor.cursor.line then