button.lua

local button = {}

local function trackButton(event)
    local button = event.target
    if event.phase == "began" then
        display.getCurrentStage():setFocus(button)
        button._isFocused = true
        button._down = true
        button:dispatchEvent{name='Button.State'; target=button, down=true}
    elseif button._isFocused then
        if event.phase == "moved" then
            local bounds = button.contentBounds
            local isWithinBounds = bounds.xMin <= event.x and bounds.xMax >= event.x and bounds.yMin <= event.y and bounds.yMax >= event.y
            if isWithinBounds ~= button._down then
                button._down = isWithinBounds
                button:dispatchEvent{name='Button.State'; target=button, down=button._down}
            end
        elseif event.phase == "ended" or event.phase == "cancelled" then
            button:dispatchEvent{name='Button.State'; target=button, down=false}
            button:dispatchEvent{name='Button'; target=button, activate=button._down and event.phase == "ended"}
            display.getCurrentStage():setFocus(button, nil)
            button._down = nil
            button._isFocused = nil
        end
    end
    return true
end

function button.new(object)
    object:addEventListener('touch', trackButton)
end

local function spriteButton(event)
    event.target.currentFrame = event.down and 2 or 1
end

function button.sprite(object)
    object = button.new(object)
    object:addEventListener('Button.State', spriteButton)
    return object
end

return button