revert commit 4c8960b5c7

Well, almost. I'm just reminding myself of the sort of plumbing I need,
not reintroducing the old logic that never worked right and had
undergone n iterations of corruption.

0019-B

@@ -1,4 +1,4 @@
-B = function()
+B = function(preserve_screen_top_of_cursor_node)
 	-- recompute various aspects based on the current viewport settings
 	for _,obj in ipairs(Surface) do
 		if obj.type == 'line' then
@@ -16,10 +16,10 @@ B = function()
 			obj.zdata = love.math.newBezierCurve(zdata):render()
 		elseif obj.type == 'text' then
 			if obj.w then
-				update_editor_box(obj)
+				update_editor_box(obj, preserve_screen_top_of_cursor_node)
 			else
 				obj.text = love.graphics.newText(love.graphics.getFont(), obj.data)
 			end
 		end
 	end
-end
+end

0021-compute_layout

@@ -1,4 +1,4 @@
-compute_layout = function(node, x,y, nodes_to_render)
+compute_layout = function(node, x,y, nodes_to_render, preserve_screen_top_of_cursor_node)
 	-- append to nodes_to_render flattened instructions to render a hierarchy of nodes
 	-- return x,y rendered until (surface coordinates)
 	if node.type == 'text' then
@@ -31,7 +31,7 @@ compute_layout = function(node, x,y, nodes_to_render)
 		if node.editor == nil then
 			initialize_editor(node)
 		else
-			update_editor_box(node)
+			update_editor_box(node, preserve_screen_top_of_cursor_node)
 		end
 		node.h = box_height(node)
 		table.insert(nodes_to_render, node)

0022-on.text_input

@@ -5,6 +5,6 @@ on.text_input = function(t)
 		if not eq(Cursor_node.editor.screen_top1, old_top) then
 			Viewport.y = Cursor_node.y + y_of_schema1(Cursor_node.editor, Cursor_node.editor.screen_top1)
 		end
-		A()
+		A(--[[preserve screen_top of cursor node]] true)
 	end
-end
+end

0023-on.keychord_press

@@ -22,7 +22,7 @@ on.keychord_press = function(chord, key)
 		if not eq(Cursor_node.editor.screen_top1, old_top) then
 			Viewport.y = Cursor_node.y + y_of_schema1(Cursor_node.editor, Cursor_node.editor.screen_top1)
 		end
-		A()
+		A(--[[preserve screen_top of cursor node]] true)
 	else
 		if chord == 'up' then
 			Viewport.y = Viewport.y - scale(20)

0028-A

@@ -1,8 +1,8 @@
-A = function()
+A = function(preserve_screen_top_of_cursor_node)
 	love.graphics.setFont(love.graphics.newFont(scale(20)))  -- editor objects implicitly depend on current font
 	Surface = {}
 	compute_layout(Page, Page.x,Page.y, Surface)
 	-- continue the pipeline
-	B()
+	B(preserve_screen_top_of_cursor_node)
 	-- TODO: ugly that we're manipulating editor objects twice
-end
+end

0030-update_editor_box

@@ -1,4 +1,4 @@
-update_editor_box = function(node)
+update_editor_box = function(node, preserve_screen_top_of_cursor_node)
 	if node.editor == nil then return end
 	edit.update_font_settings(node.editor, scale(20))
 	if node.y > Viewport.y then
@@ -14,4 +14,4 @@ update_editor_box = function(node)
 	node.editor.right = math.ceil(vx(node.x+node.w))
 	node.editor.width = node.editor.right - node.editor.left
 	Text.redraw_all(node.editor)
-end
+end