another bugfix in scrolling while inserting text

I'm being unprincipled at the moment between pos and x,y coordinates.
Whatever is more convenient. Perhaps a cleaner approach will come to me
over time.

main.lua

@@ -166,6 +166,7 @@ function App.draw()
               Text.draw_cursor(25, y)
             end
           end
+        Screen_bottom1.pos = Screen_top1.pos
         y = y + Line_height
       elseif line.mode == 'drawing' then
         y = y+10 -- padding

text.lua

@@ -156,9 +156,8 @@ function Text.insert_at_cursor(t)
   Lines[Cursor1.line].data = string.sub(Lines[Cursor1.line].data, 1, byte_offset-1)..t..string.sub(Lines[Cursor1.line].data, byte_offset)
   Lines[Cursor1.line].fragments = nil
   Lines[Cursor1.line].screen_line_starting_pos = nil
-  local scroll_down = Text.le1(Screen_bottom1, Cursor1)
   Cursor1.pos = Cursor1.pos+1
-  if scroll_down then
+  if Cursor_y >= App.screen.height - Line_height then
     Text.populate_screen_line_starting_pos(Cursor1.line)
     Text.snap_cursor_to_bottom_of_screen()
 --?     print('=>', Screen_top1.line, Screen_top1.pos, Cursor1.line, Cursor1.pos, Screen_bottom1.line, Screen_bottom1.pos)

text_tests.lua

@@ -132,7 +132,7 @@ end
 
 function test_insert_from_clipboard()
   io.write('\ntest_insert_from_clipboard')
-  -- display a few lines with cursor on bottom line
+  -- display a few lines
   App.screen.init{width=25+30, height=60}
   Lines = load_array{'abc', 'def', 'ghi', 'jkl'}
   Line_width = App.screen.width
@@ -146,7 +146,7 @@ function test_insert_from_clipboard()
   App.screen.check(y, 'def', 'F - test_insert_from_clipboard/baseline/screen:2')
   y = y + Line_height
   App.screen.check(y, 'ghi', 'F - test_insert_from_clipboard/baseline/screen:3')
-  -- after hitting the enter key the screen scrolls down
+  -- paste some text including a newline, check that new line is created
   App.clipboard = 'xy\nz'
   App.run_after_keychord('C-v')
   check_eq(Screen_top1.line, 1, 'F - test_insert_from_clipboard/screen_top')
@@ -736,6 +736,25 @@ function test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom()
   App.screen.check(y, 'kl', 'F - test_enter_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:2')
 end
 
+function test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom()
+  io.write('\ntest_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom')
+  -- display just an empty bottom line on screen
+  App.screen.init{width=25+30, height=60}
+  Lines = load_array{'abc', ''}
+  Line_width = App.screen.width
+  Cursor1 = {line=2, pos=1}
+  Screen_top1 = {line=2, pos=1}
+  Screen_bottom1 = {}
+  App.draw()
+  -- after hitting the inserting_text key the screen does not scroll down
+  App.run_after_textinput('a')
+  check_eq(Screen_top1.line, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen_top')
+  check_eq(Cursor1.line, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:line')
+  check_eq(Cursor1.pos, 2, 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/cursor:pos')
+  local y = Margin_top
+  App.screen.check(y, 'a', 'F - test_inserting_text_on_final_line_avoids_scrolling_down_when_not_at_bottom/screen:1')
+end
+
 function test_typing_on_bottom_line_scrolls_down()
   io.write('\ntest_typing_on_bottom_line_scrolls_down')
   -- display a few lines with cursor on bottom line