Code snippets for the Corona SDK Tutorial: Game controllers and axes (https://coronalabs.com/blog/2013/09/24/tutorial-controllers-and-axis)

part5.lua

local function onAxisEvent( event )

    -- Display some info on the screen about this axis event
    local message = "Axis '" .. event.axis.descriptor .. "' was moved " .. tostring( event.normalizedValue )
    myAxisDisplayText.text = message

    -- Map event data to simple variables
    local abs = math.abs
    local controller = event.device.descriptor
    local thisAxis = event.axis.number
    local thisPlayer

    -- Check which controller this is coming from; you can trust the names
    -- "Joystick 1" and "Joystick 2" to represent player 1, player 2, etc.
    -- Based on the controller for this event, pick the object to manipulate

    if ( controller == "Joystick 1" ) then
        thisPlayer = redPlayer
    elseif ( controller == "Joystick 2" ) then
        thisPlayer = greenPlayer
    end

    -- Now that we know which controller it is, determine which axis to measure
    -- Because the "right trigger" might be 6 on one brand of controller
    -- but 14 on another, we use the mapping system described above

    if ( axis[controller]["left_x"] and axis[controller]["left_x"] == thisAxis ) then

        -- This helps handle noisy sticks and sticks that don't settle back to 0 exactly
        -- You can adjust the value based on the sensitivity of the stick
        -- If the stick is moved far enough, then move the player, else force it to
        -- settle back to a zero value

        -- Set the X distance in the player object so the enterFrame function can move it

       if ( abs(event.normalizedValue) > 0.15 ) then
           thisPlayer.isMovingX = event.normalizedValue
       else
           thisPlayer.isMovingX = 0
       end

       -- Draw the blue dot around the center to show how far you actually moved the stick
       blueDot.x = display.contentCenterX + event.normalizedValue * 10

    elseif ( axis[controller]["left_y"] and axis[controller]["left_y"] == thisAxis ) then

       -- Just like X, now handle the Y axis

       if ( abs(event.normalizedValue) > 0.15 ) then
           thisPlayer.isMovingY = event.normalizedValue
       else
           thisPlayer.isMovingY = 0
       end

       -- Move the blue dot
       blueDot.y = display.contentCenterY + event.normalizedValue * 10

    elseif ( axis[controller]["right_x"] and axis[controller]["right_x"] == thisAxis ) then

        -- We will use the right stick to rotate our player
        thisPlayer.isRotatingX = event.normalizedValue

        -- Use Pythagoras' Theorem to compute the distance the stick is moved from center

        local a = math.abs( thisPlayer.isRotatingX * thisPlayer.isRotatingX )
        local b = math.abs( thisPlayer.isRotatingY * thisPlayer.isRotatingY )
        local d = math.sqrt( a + b )

        -- If the distance isn't very far, set it to zero to account for
        -- stick "slop" and not settling back to perfect center

        if ( d < 0.15 ) then
            thisPlayer.rotationDistance = 0
        else

            -- In the Runtime enterFrame listener we look at the current angle and the
            -- last angle to determine which direction we need to rotate

            thisPlayer.rotationDistance = d * 3
            thisPlayer.lastAngle = thisPlayer.thisAngle
            thisPlayer.thisAngle = math.floor( calculateAngle(thisPlayer.isRotatingX, thisPlayer.isRotatingY) )
        end

    elseif ( axis[controller]["right_y"] and axis[controller]["right_y"] == thisAxis ) then

        -- Repeat for the Y axis on the right stick
        thisPlayer.isRotatingY = event.normalizedValue

        local a = math.abs( thisPlayer.isRotatingX * thisPlayer.isRotatingX )
        local b = math.abs( thisPlayer.isRotatingY * thisPlayer.isRotatingY )
        local d = math.sqrt( a + b )

        if ( d < 0.15 ) then
            thisPlayer.rotationDistance = 0
        else
            thisPlayer.rotationDistance = d * 3
            thisPlayer.lastAngle = thisPlayer.thisAngle
            thisPlayer.thisAngle = math.floor( calculateAngle(thisPlayer.isRotatingX, thisPlayer.isRotatingY) )
        end

    elseif ( axis[controller]["left_trigger"] or axis[controller]["right_trigger"] == thisAxis ) then

        -- Use the analog triggers to gradually change the color of the player
        -- No trigger pressure will be full brightness
        -- The more you squeeze the trigger, the darker the square gets

        local color = 1 * (1 - event.normalizedValue)
        if ( color < 0.125 ) then
            color = 0.125
        elseif ( color >= 1 ) then
            color = 1
        end

        if ( thisPlayer.color == "red" ) then
            thisPlayer:setFillColor( color, 0, 0 )
        else
            thisPlayer:setFillColor( 0, color, 0 )
        end
    end

    return true
end

Runtime:addEventListener( "axis", onAxisEvent )