snapshot: insight

Ugh, it's been in front of my eyes all along. The logs have been
repeatedly showing a recurrence within a single frame:

key press -> update Viewport.y from screen_top -> A -> B -> update_editor_box -> update screen_top from Viewport.y

We need both those updates, but both should never occur at the same
time to the same node.

I think this is why screen panning works if I take out the scale inside
update_editor_box: the scale has already happened "once" in
updating Viewport.y, and it doesn't converge if we perform it a second
time in a frame. But the solution is just to do one or the other to a
node, never both.

I knew this (learned it the hard way) when I first built pensieve.love,
and I had an assertion to avoid it. But my assertion was brittle, and it
kept failing, and I took it out, and then I slowly took out all the code
that prevented this recurrence.

0020-Page

@@ -70,7 +70,7 @@ Page = {
 '59',
 '60',
 		},
-        width=400, bg={r=1,g=1,b=0}
+        width=400, bg={r=0,g=0.8,b=0}
       },
     },
-}
+}

0026-on.draw

@@ -1,9 +1,18 @@
 on.draw = function()
 	love.graphics.setColor(0,0,0)
+	love.graphics.line(50, 0, 50, App.screen.height)
+	for i=0,100 do
+		love.graphics.print(tostring(i), 30, i*100)
+	end
+	local vy0 = vy(0)
+	love.graphics.line(100, vy0, 100, App.screen.height)
+	for i=0,100 do
+		love.graphics.print(tostring(i), 80, vy0+i*100)
+	end
 	love.graphics.line(vx(0), vy(0), vx(0), vy(1000000))
 	love.graphics.line(vx(0), vy(0), vx(1000000), vy(0))
 	for i=0,100 do
-		love.graphics.print(tostring(i), vx(0), vy(i*100))
+		love.graphics.print(tostring(i), vx(0)-20, vy(i*100))
 	end
 	for _,obj in ipairs(Surface) do
 		love.graphics.setColor(obj.r or 0, obj.g or 0, obj.b or 0)
@@ -27,4 +36,4 @@ on.draw = function()
 			end
 		end
 	end
-end
+end

0028-A

@@ -1,17 +1,8 @@
 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
-	local red = false
-	for x=-1000,2000,300 do
-		for y=-10000,10000,200 do
-			add_thick_line({type='line', data={x,y, x+200,y+200, x,y+400}, r=red and 1 or 0,g=red and 0 or 0.5,b=0}, 10)
-			red = not red
-		end
-	end
+	Surface = {}
 	compute_layout(Page, Page.x,Page.y, Surface)
-	compute_layout(Page2, Page2.x,Page2.y, Surface)
 	-- continue the pipeline
 	B()
 	-- TODO: ugly that we're manipulating editor objects twice
-end
+end

0030-update_editor_box

@@ -1,5 +1,6 @@
 update_editor_box = function(node)
 	if node.editor == nil then return end
+	edit.update_font_settings(node.editor, scale(20))
 	if node.y > Viewport.y then
 		if node ~= Cursor_node then
 			node.editor.screen_top1.line = 1
@@ -12,6 +13,5 @@ update_editor_box = function(node)
 	node.editor.left = math.floor(vx(node.x))
 	node.editor.right = math.ceil(vx(node.x+node.w))
 	node.editor.width = node.editor.right - node.editor.left
-	edit.update_font_settings(node.editor, scale(20))
 	Text.redraw_all(node.editor)
 end

0034-dump_state

@@ -1,10 +1,13 @@
 dump_state = function()
 	print('===')
 	print('zoom', Viewport.zoom)
-	print('viewport', Viewport.y)
-	print('node', Page.data[1].y)
-	print('node renders from', Page.data[1].editor.top)
-	print('screen top', Page.data[1].editor.screen_top1.line)
+	print('viewport', Viewport.y, 'spx')
+	local node = Page.data[1]
+	print('node', node.y, 'spx')
+	print('line height', node.editor.line_height, 'vpx')
+	print('node renders from', node.editor.top, 'vpx')
+	print('screen top', node.editor.screen_top1.line)
+	print('invariant', Viewport.y-node.y+node.editor.top - y_of_schema1(node.editor, node.editor.screen_top1))
 	local l = 25
-	print('y of line', l, y_of_schema1(Page.data[1].editor, {line=l, pos=1}))
+	print('y of line', l, y_of_schema1(node.editor, {line=l, pos=1}), 'spx')
 end