greatly simplify layout

I don't know why this was so hard, but I don't need this variable
preserve_screen_top_of_cursor_node at all. We only set it when the
cursor is in some node, but we also only check for when the current node
is the cursor. Comparing with a nil cursor node works just as well.

I've also checked that driver.love doesn't need
preserve_screen_top_of_cursor_node. I think it came from pensieve.love,
where I've since taken it out. Did I ever need it even there?

0019-B

@@ -1,4 +1,4 @@
-B = function(preserve_screen_top_of_cursor_node)
+B = function()
 	-- recompute various aspects based on the current viewport settings
 	love.graphics.setFont(love.graphics.newFont(scale(20)))  -- editor objects implicitly depend on current font so update it
 	for _,obj in ipairs(Surface) do
@@ -17,10 +17,10 @@ B = function(preserve_screen_top_of_cursor_node)
 			obj.zdata = love.math.newBezierCurve(zdata):render()
 		elseif obj.type == 'text' then
 			if obj.w then
-				update_editor_box(obj, preserve_screen_top_of_cursor_node)
+				update_editor_box(obj)
 			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, preserve_screen_top_of_cursor_node)
+compute_layout = function(node, x,y, nodes_to_render)
 	-- 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, preserve_screen_top_of_cur
 		if node.editor == nil then
 			initialize_editor(node)
 		else
-			update_editor_box(node, preserve_screen_top_of_cursor_node)
+			update_editor_box(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(--[[preserve screen_top of cursor node]] true)
+		A()
 	end
-end
+end

0023-on.keychord_press

@@ -17,7 +17,7 @@ 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(--[[preserve screen_top of cursor node]] true)
+		A()
 	else
 		if chord == 'up' then
 			Viewport.y = Viewport.y - scale(20)
@@ -51,4 +51,4 @@ on.keychord_press = function(chord, key)
 			B()
 		end
 	end
-end
+end

0028-A

@@ -1,4 +1,4 @@
-A = function(preserve_screen_top_of_cursor_node)
+A = function()
 	love.graphics.setFont(love.graphics.newFont(scale(20)))  -- editor objects implicitly depend on current font
 	-- translate Page to Surface
 	while #Surface > 3 do table.remove(Surface) end  -- HACK
@@ -9,9 +9,9 @@ A = function(preserve_screen_top_of_cursor_node)
 			red = not red
 		end
 	end
-	compute_layout(Page, Page.x,Page.y, Surface, preserve_screen_top_of_cursor_node)
-	compute_layout(Page2, Page2.x,Page2.y, Surface, preserve_screen_top_of_cursor_node)
+	compute_layout(Page, Page.x,Page.y, Surface)
+	compute_layout(Page2, Page2.x,Page2.y, Surface)
 	-- continue the pipeline
-	B(preserve_screen_top_of_cursor_node)
+	B()
 	-- TODO: ugly that we're manipulating editor objects twice
 end

0030-update_editor_box

@@ -1,8 +1,8 @@
-update_editor_box = function(node, preserve_screen_top_of_cursor_node)
+update_editor_box = function(node)
 	if node.editor == nil then return end
 	-- Compute screen_top1 in viewport coordinates because the editor's font takes scaling into account.
 	if vy(node.y) > 0 then
-		if not preserve_screen_top_of_cursor_node or node ~= Cursor_node then
+		if node ~= Cursor_node then
 			node.editor.screen_top1.line = 1
 			node.editor.screen_top1.pos = 1
 		end