I bought Codea a couple of days ago, and now I’m trying to understand the workings of Lua by studying the examples. In the multi touch example there’s something I don’t quite understand:
-- Use this function to perform your initial setup
function setup()
print("This example tracks multiple touches and colors them based on their ID")
-- keep track of our touches in this table
touches = {}
end
function touched(touch)
if touch.state == ENDED then
touches[touch.id] = nil
else
touches[touch.id] = touch
end
end
-- This function gets called once every frame
function draw()
background(0, 0, 0, 255)
for k,touch in pairs(touches) do
-- Use the touch id as the random seed
math.randomseed(touch.id)
-- This ensures the same fill color is used for the same id
fill(math.random(255),math.random(255),math.random(255))
-- Draw ellipse at touch position
ellipse(touch.x, touch.y, 100, 100)
end
end
It seems the function touched() stores every new touch in the table ‘touches’, but where is it called? And even though it’s not called anywhere, it’s apparantly executed every step.
touched is a built in event, called automatically when you touch the screen, and it is checked between each call to draw.
You may find it easier to start with Lua (touch is really part of the extra functionality added by Codea). The wiki page has links, and I have an ebook here
touched(touch) is called by Codea whenever a touch occurs, changes state, or ends. It is called once per-state change per-touch.
So if I put one finger on the screen, Codea might call the touched() method as follows:
touched( touch ) -- With touch.state == BEGAN
touched( touch ) -- With touch.state == MOVING
touched( touch ) -- With touch.state == MOVING
... MOVING sent for every time the touch changes position, even slightly
touched( touch ) -- ENDED (I lifted my finger)
If I place two fingers on the screen, Codea might call the touched() method as follows:
touched( t1 ) -- With state BEGAN
touched( t1 ) -- With state MOVING
touched( t1 ) -- With state MOVING
touched( t2 ) -- With state BEGAN
touched( t1 ) -- With state MOVING
touched( t2 ) -- With state MOVING
touched( t1 ) -- With state MOVING
touched( t2 ) -- With state MOVING
touched( t1 ) -- With state MOVING
touched( t2 ) -- With state MOVING
... and so on
touched( t2 ) -- With state ENDED
touched( t1 ) -- With state MOVING
touched( t1 ) -- With state MOVING
touched( t1 ) -- With state ENDED
Because your fingers won’t touch the screen at exactly the same time (or lift at exactly the same time) you won’t get touch events perfectly timed together.
Thank you both for the quick reply and clear explanation, I appreciate it. Also, I read the ebook, it was really helpful. I have a little bit experience with programming, so it was quick to understand.