koreader/frontend/ui/widget/container/centercontainer.lua

local WidgetContainer = require("ui/widget/container/widgetcontainer")

--[[
CenterContainer centers its content (1 widget) within its own dimensions
--]]
local CenterContainer = WidgetContainer:new()

function CenterContainer:paintTo(bb, x, y)
    local contentSize = self[1]:getSize()
    if contentSize.w > self.dimen.w or contentSize.h > self.dimen.h then
        -- throw error? paint to scrap buffer and blit partially?
        -- for now, we ignore this
    end
    local x_pos = x
    local y_pos = y
    if self.ignore ~= "height" then
        y_pos = y + math.floor((self.dimen.h - contentSize.h)/2)
    end
    if self.ignore ~= "width" then
        x_pos = x + math.floor((self.dimen.w - contentSize.w)/2)
    end
    self[1]:paintTo(bb, x_pos, y_pos)
end

return CenterContainer