function log(stack_frame_index, obj)
	local info = debug.getinfo(stack_frame_index, 'Sl')
	local msg
	if type(obj) == 'string' then
		msg = obj
	else
		msg = json.encode(obj)
	end
	love.filesystem.append('log', info.short_src..':'..info.currentline..': '..msg..'\n')
end

function log_state(stack_frame_index)
	if stack_frame_index == nil then
		stack_frame_index = 3
	end
	log(stack_frame_index, {name='state', Ballp=Ballp, Ballv=Ballv, A=A, B=B})
end

-- for section delimiters we'll use specific Unicode box characters
function log_start(name, stack_frame_index)
	if stack_frame_index == nil then
		stack_frame_index = 3
	end
	-- I'd like to use the unicode character \u{250c} here, but it doesn't work
	-- in OpenBSD.
	log(stack_frame_index, '[ u250c ' .. name)
end
function log_end(name, stack_frame_index)
	if stack_frame_index == nil then
		stack_frame_index = 3
	end
	-- I'd like to use the unicode character \u{2518} here, but it doesn't work
	-- in OpenBSD.
	log(stack_frame_index, '] u2518 ' .. name)
end

function log_new(name, stack_frame_index)
	if stack_frame_index == nil then
		stack_frame_index = 4
	end
	log_end(name, stack_frame_index)
	log_start(name, stack_frame_index)
end

-- rendering graphical objects within sections/boxes
log_render = {}

Ball_color = {r=0.5, g=0, b=0.5}
A_color = {r=0, g=0.5, b=0}
B_color = {r=0, g=0, b=0.5}

function log_render.state(state, x,y, w)
	-- emit drawing to given space on screen (x to x+w, y downward); return lowest y drawn
	local h = 100
	love.graphics.rectangle('line', x+30,y, 100,h)
	local starty = y
	-- translate coordinate system
	x,y = x+30+50, y+50
	-- render -- with the actual numbers as Tufte commands
	App.color(Ball_color)
	love.graphics.circle('fill', x+state.Ballp.x, y+state.Ballp.y, 3)
	love.graphics.print(('%d,%d'):format(state.Ballp.x, state.Ballp.y), x+state.Ballp.x-40, y+state.Ballp.y-40)
	love.graphics.line(x+state.Ballp.x, y+state.Ballp.y, x+state.Ballp.x+state.Ballv.x*100, y+state.Ballp.y+state.Ballv.y*100)
	love.graphics.print(('Ball velocity: %0.2f,%0.2f'):format(state.Ballv.x, state.Ballv.y), x+200,starty+50)
--? 	love.graphics.print(('%0.2f,%0.2f -> %0.2f,%0.2f'):format(x+state.Ballp.x, y+state.Ballp.y, x+state.Ballp.x+state.Ballv.x, y+state.Ballp.y+state.Ballv.y), x+200, starty+50)  -- heh, debug prints for my debug prints
	App.color(A_color)
	love.graphics.rectangle('fill', x-50, y+state.A.ymin, 3, state.A.ymax-state.A.ymin)
	App.color(B_color)
	love.graphics.rectangle('fill', x+50-3+1, y+state.B.ymin, 3, state.B.ymax-state.B.ymin)
	App.color(Text_color)
	--
	return h+20
end

-- vim:noexpandtab