Zoom In Out Pinch

--gestures
--this could be improved by considering angles between tocuhes
--angles could be used to zoom in on something other than the center
--angles could also be used for rotate behavior
function setup()
    --create a table of 10 random shapes[drawn as ellipses in draw()]
    s = {}
    for i = 1,10 do
        x = math.random() * WIDTH
        y = math.random() * HEIGHT
        w = math.random() * WIDTH
        h = math.random() * HEIGHT
        s[i] = {x=x,y=y,w=w,h=h}
    end
    --set up two touch tables
    t1 = {id=nil}
    t2 = {id=nil}
    --set current scale, 1 is 100%
    cs = 1
end

function touched(touch)
    if touch.state == BEGAN then
        --store two touches
        if t1.id == nil then
            t1 = touch
        elseif t2.id == nil then
            t2 = touch
        end
    elseif touch.state == MOVING then
        if (t1.id ~= nil) and (t2.id ~= nil) then
            --if we have both touches active
            if touch.id == t1.id then
                --determine the current (cd) and previous (pd)
                --distances between the two touches
                --using the movement of the first touch
                t1 = touch
                --the systems keeps prevX and PrevY updated
                --(you won't find them set anywhere in this code)
                pv = vec2(t1.prevX,t1.prevY)
                t1v = vec2(t1.x,t1.y)
                t2v = vec2(t2.x,t2.y)
                cd = t1v:dist(t2v)
                pd = pv:dist(t2v)
            end
            if touch.id == t2.id then
                --using the movement of the first touch
                t2 = touch
                pv = vec2(t2.prevX,t2.prevY)
                t1v = vec2(t1.x,t1.y)
                t2v = vec2(t2.x,t2.y)
                cd = t1v:dist(t2v)
                pd = pv:dist(t1v)
            end
            --recaculate current scale
            --based on the change in current and previous distance
            cs = cs * (cd/pd)
        end
    else --if touch.state == ENDED then
        if t1.id ~= nil then
            if touch.id == t1.id then
                --forget touch 1
                t1 = {id=nil}
            end
        end
        if t2.id ~= nil then
            if touch.id == t2.id then
                --forget touch 2
                t2 = {id=nil}
            end
        end
    end
end

function draw()
    background(0,0,0,255)
    --scale the drawing area to the current scale
    scale(cs)
    --keep the shapes in the center
    --without this zoom out would push everthing to the lower right
    translate((WIDTH/2/cs)-WIDTH/2,(HEIGHT/2/cs)-HEIGHT/2)
    strokeWidth(30)
    stroke(0, 255, 57, 255)
    fill(6, 10, 239, 255)
    for i = 1,10 do
        ellipse(s[i].x,s[i].y,s[i].w,s[i].h)
    end
end