koreader/frontend/apps/reader/modules/readerrotation.lua

local InputContainer = require("ui/widget/container/inputcontainer")
local Device = require("device")
local Event = require("ui/event")
local _ = require("gettext")

local ReaderRotation = InputContainer:new{
    current_rotation = 0
}

function ReaderRotation:init()
    if Device:hasKeyboard() then
        self.key_events = {
            -- these will all generate the same event, just with different arguments
            RotateLeft = {
                {"J"},
                doc = "rotate left by 90 degrees",
                event = "Rotate", args = -90 },
            RotateRight = {
                {"K"},
                doc = "rotate right by 90 degrees",
                event = "Rotate", args = 90 },
        }
    end
end

--- @todo Reset rotation on new document, maybe on new page?

function ReaderRotation:onRotate(rotate_by)
    self.current_rotation = (self.current_rotation + rotate_by) % 360
    self.ui:handleEvent(Event:new("RotationUpdate", self.current_rotation))
    return true
end

return ReaderRotation