display.setStatusBar( display.HiddenStatusBar )
 
local halfW = display.contentCenterX
local halfH = display.contentCenterY
 
-- Black background
local bkg = display.newRect( 0, 0, 768, 1024 )
bkg:setFillColor( 0 )
 
-- Image to be masked
local image = display.newImageRect( "image.png", 768, 1024 )
image:translate( halfW, halfH )
 
-- Mask
local mask = graphics.newMask( "circlemask.png" )
image:setMask( mask )
 
 
local radiusMax = math.sqrt( halfW*halfW + halfH*halfH )
 
function onTouch( event )
        local t = event.target
 
        local phase = event.phase
        if "began" == phase then
                display.getCurrentStage():setFocus( t )
 
                -- Spurious events can be sent to the target, e.g. the user presses 
                -- elsewhere on the screen and then moves the finger over the target.
                -- To prevent this, we add this flag. Only when it's true will "move"
                -- events be sent to the target.
                t.isFocus = true
 
                -- Store initial position
                t.x0 = event.x - t.maskX
                t.y0 = event.y - t.maskY
        elseif t.isFocus then
                if "moved" == phase then
                        -- Make object move (we subtract t.x0,t.y0 so that moves are
                        -- relative to initial grab point, rather than object "snapping").
                        local maskX = event.x - t.x0
                        local maskY = event.y - t.y0
                        t.maskX = maskX
                        t.maskY = maskY
 
                        -- Stretch the flashlight as it moves further away 
                        -- from the screen's center
                        local radius = math.sqrt( maskX*maskX + maskY*maskY )
                        local scaleDelta = radius/radiusMax
                        t.maskScaleX = 1 + scaleDelta
                        t.maskScaleY = 1 + 0.2 * scaleDelta
 
                        -- Rotate it appropriately about screen center
                        local rotation = math.deg( math.atan2( maskY, maskX ) )
                        t.maskRotation = rotation
 
                elseif "ended" == phase or "cancelled" == phase then
                        display.getCurrentStage():setFocus( nil )
                        t.isFocus = false
                end
        end
 
        return true
end
image:addEventListener( "touch", onTouch )
 
-- Display instructions
local labelFont = "Zapfino" -- if not found, system font will be used
local myLabel = display.newText( "Touch circle to move flashlight", 0, 0, labelFont, 34 )
myLabel:setTextColor( 255, 255, 255, 180 )
myLabel.x = halfW
myLabel.y = 200