rotating object around point or other object using touch corona sdk

Question

I am trying to have a number of boxes rotate like a ferris wheel based on touch input

so imagine a ferris wheel on the screen and dragging one of the carts down would rotate the wheel one way and dragging up would rotate the wheel the other way

each box or 'cart' on the ferris wheel doesnt rotate they will only move in a circular motion, exactly like a ferris wheel

i pretty much have this working now, however my boxes are snapping away from the initial grab point so when i touch one of the boxes it will quickly appear elsewhere but then rotate as normal, i want it to continue to rotate smoothly from initial grab point

here is my current code below

local squares = display.newGroup()

local square = display.newRect(0,0,200,200)
square.x, square.y = 320, 320
square:setFillColor(100,255,55)
squares:insert(square)

local square2 = display.newRect(0,0,200,200)
square2.x, square2.y = 320, 320
square2:setFillColor(999,255,55)
squares:insert(square2)

local function onTouch( event )
local t = event.target

local phase = event.phase
if "began" == phase then

    local parent = t.parent
    parent:insert( t )
    display.getCurrentStage():setFocus( t )
    t.isFocus = true

    -- Store initial position
    t.x0 = event.x - t.x
    t.y0 = event.y - t.y

elseif t.isFocus then
    if "moved" == phase then

   local degrees = event.y

        local rads = degrees * (math.pi / 360.0)
            square.x = 300 * math.cos(rads) + 500
            square.y = 300 * math.sin(rads)+ 500
            degrees = degrees + 100
           print (square.x, square.y)

         local rads2 = degrees * (math.pi / 360.0)
            square2.x = 300 * math.cos(rads2)+ 500
            square2.y = 300 * math.sin(rads2)+ 500
            degrees = degrees - 100

           print (square.x, square.y)




    elseif "ended" == phase or "cancelled" == phase then
        display.getCurrentStage():setFocus( nil )
        t.isFocus = false
    end
end
return true
end


squares:addEventListener( "touch", onTouch )

please feel free to point out any silly mistakes I have made and also if you could show me how to get the same affect but around another object rather than a point i would be really greatful, thanks

Answer 1

This is a complete working example.

local squares = display.newGroup()

local wheelX =  display.contentCenterX
local wheelY =  display.contentCenterY

local radius = 220
local degrees = -180
local squareH = 150

local square = display.newRect(0,0,squareH,squareH)
square:setFillColor(255,255,255)
square.degStart = 100
squares:insert(square)

local square2 = display.newRect(0,0,squareH,squareH)
square2:setFillColor(999,255,55)
square2.degStart = -10
squares:insert(square2)


local function drawRects(degrees)
    local rads = (square.degStart + degrees) * (math.pi / 180.0)
    square.x = radius * math.cos(rads) + wheelX
    square.y = radius * math.sin(rads) + wheelY

    local rads2 = (square2.degStart + degrees) * (math.pi / 180.0)
    square2.x = radius * math.cos(rads2) + wheelX
    square2.y = radius * math.sin(rads2) + wheelY
end

local function getDegrees(square)
    local x = square.x
    local y = square.y

    local degrees = math.atan2((y - wheelY) , (x - wheelX)) * (180 / math.pi)

    return degrees
end


local function onTouch( event )
    local t = event.target

    local phase = event.phase
    local parent = t.parent

    if "began" == phase then
        print("began")
        parent:insert( t )
        display.getCurrentStage():setFocus( t )
        t.isFocus = true

        square.degStart = getDegrees(square)
        square2.degStart = getDegrees(square2)
    elseif t.isFocus then
        if "moved" == phase then
            degrees = math.atan2((event.yStart - wheelY) , (event.xStart - wheelX)) * (180 / math.pi)

            degrees2 = math.atan2((event.y - wheelY) , (event.x - wheelX)) * (180 / math.pi)

            diffDegrees = degrees2 - degrees
            drawRects(diffDegrees)

            print("diffDegrees: " .. diffDegrees)
        elseif "ended" == phase or "cancelled" == phase then
            display.getCurrentStage():setFocus( nil )
            t.isFocus = false
        end
    end
return true
end

squares:addEventListener( "touch", onTouch )

drawRects(degrees)

It took me a lot of time.

Answer 2

You should try to get event.y and event.x and then retrieve the degrees with formula:

degrees = Math.atan(event.y / event.x)