corona sdk pinch to zoom - lua

Question

i am using the function contained in corona sample codes for the pinch to zoom. But since i am developing an app, i need to make every single place of interest zoommable. Do i have to copy and paste the horribly long function for every single image or can i redirect every image on just one function? I am new to lua, here is the pinch to zoom function included in the sample code:
function background:touch( event )
local result = true
local phase = event.phase
local previousTouches = self.previousTouches
local numTotalTouches = 1
if ( previousTouches ) then
-- add in total from previousTouches, subtract one if event is already in the array
numTotalTouches = numTotalTouches + self.numPreviousTouches
if previousTouches[event.id] then
numTotalTouches = numTotalTouches - 1
end
end
if "began" == phase then
-- Very first "began" event
if ( not self.isFocus ) then
-- Subsequent touch events will target button even if they are outside the contentBounds of button
display.getCurrentStage():setFocus( self )
self.isFocus = true
previousTouches = {}
self.previousTouches = previousTouches
self.numPreviousTouches = 0
elseif ( not self.distance ) then
local dx,dy
if previousTouches and ( numTotalTouches ) >= 2 then
dx,dy = calculateDelta( previousTouches, event )
end
-- initialize to distance between two touches
if ( dx and dy ) then
local d = math.sqrt( dx*dx + dy*dy )
if ( d > 0 ) then
self.distance = d
self.xScaleOriginal = self.xScale
self.yScaleOriginal = self.yScale
print( "distance = " .. self.distance )
end
end
end
if not previousTouches[event.id] then
self.numPreviousTouches = self.numPreviousTouches + 1
end
previousTouches[event.id] = event
elseif self.isFocus then
if "moved" == phase then
if ( self.distance ) then
local dx,dy
if previousTouches and ( numTotalTouches ) >= 2 then
dx,dy = calculateDelta( previousTouches, event )
end
if ( dx and dy ) then
local newDistance = math.sqrt( dx*dx + dy*dy )
local scale = newDistance / self.distance
print( "newDistance(" ..newDistance .. ") / distance(" .. self.distance .. ") = scale(".. scale ..")" )
if ( scale > 0 ) then
self.xScale = self.xScaleOriginal * scale
self.yScale = self.yScaleOriginal * scale
end
end
end
if not previousTouches[event.id] then
self.numPreviousTouches = self.numPreviousTouches + 1
end
previousTouches[event.id] = event
elseif "ended" == phase or "cancelled" == phase then
if previousTouches[event.id] then
self.numPreviousTouches = self.numPreviousTouches - 1
previousTouches[event.id] = nil
end
if ( #previousTouches > 0 ) then
-- must be at least 2 touches remaining to pinch/zoom
self.distance = nil
else
-- previousTouches is empty so no more fingers are touching the screen
-- Allow touch events to be sent normally to the objects they "hit"
display.getCurrentStage():setFocus( nil )
self.isFocus = false
self.distance = nil
self.xScaleOriginal = nil
self.yScaleOriginal = nil
-- reset array
self.previousTouches = nil
self.numPreviousTouches = nil
end
end
end
return result
end

Answer 1

You could probably use a closure to accomplish this, assuming all of your points of interest are alike.
Example:
local function createPOI(properties)
local pointOfInterest = createPointOfInterest() -- code to create your object
--set properties based on argument
function pointOfInterest:touch(e)
--do stuff
end
pointOfInterest:addEventListner("touch")
return pointOfInterest
end
Corona has some code here that might be useful. Check the 'Multiple Touches' section.