on.mouse_press = function(x,y, mouse_button)
	if Global_state.thread == nil then
		-- we're rendering the file picker
		-- check for any button clicks
		for _,button in ipairs(Global_state.file_picker) do
			-- do nothing; everything happens on release
			-- (to avoid changing the surface between press and release)
			if in_rect(button, x,y) then
				return
			end
		end
		-- no button clicked; pan surface
		Pan = {x=Viewport.x+x/Viewport.zoom,y=Viewport.y+y/Viewport.zoom}
		return
	end
	print('mouse press', x,y)
	if Cursor_node then
		Cursor_node.show_cursor = nil
		Cursor_node = nil
	end
	if mouse_press_consumed_by_any_button(HUD, x,y, mouse_button) then
		B()
		return
	end
	local node = on_text(x,y)
	if node then
		-- position cursor in node
		Cursor_node = node
		print('within node')
		edit.mouse_press(node.editor, x,y, mouse_button)
		print('cursor at', node.editor.cursor_x, node.editor.cursor_y)
		return
	end
	local button = on_button(x,y)
	if button then
		local n, id = new_comment(button.target_id, button.depth)
		local parent = find_node(Global_state.thread, button.target_id)
		assert(parent)
		table.insert(parent.metadata.replies, id)
		save_metadata(parent)
		local item_index = find_comment_index(button.target_id)
		table.insert(Global_state.thread.data,
			item_index+1,
			n)
		A()
	end
	-- pan surface
	Pan = {x=Viewport.x+x/Viewport.zoom, y=Viewport.y+y/Viewport.zoom}
end