Please help with flick motion

I have a code where I have a control panel (simplified to a white rectangle in the code below) that I want the user to be able to drag / flick.
I got the drag functionality to work pretty well, but I can't get the flick working (acceleration caused by the drag) properly.

I think it tracked the problem to the way I calculate the acceleration in the lines:

1 2	local flickSpeed = ((localEventY-t.y0) / dT )*.001 local newYAfterAcelleration = setToWithinLimits((t.y+flickSpeed),lowestDragPos,highestDragPos

Nokia did a great writeup on kinetic scrolling: http://www.developer.nokia.com/Community/Wiki/Qt_Kinetic_scrolling_-_from_idea_to_implementation

Calculating velocity is important: v = d / t

http://ceres.hsc.edu/homepages/classes/astronomy/fall97/Mathematics/sec5.html

Thanks. The Nokia article was an interesting reading.

I was able to solve the problem by recording the initial event.y position and using it to calculate the finger distance movement. I also used a new t.direction valuable to store the direction of the last finger movement.

here is the new code if it helps anyone in the future:

-------------------
--helper function
-------------------
local function setToWithinLimits(setTo,lowerLimit,upperLimit)
        local result
        if (setTo > upperLimit ) then result = upperLimit
    elseif (setTo < lowerLimit) then result = lowerLimit
    else result = setTo
    end
    return result
end
-------------------
--objects
-------------------
 
local localGroup=display.newGroup()
 
local panelGroup = display.newGroup()
 
localGroup:insert(panelGroup)
 
local panelBG = display.newRect(0,0,200,display.contentHeight*2)
panelBG:setFillColor(255,255,255)
 
local referenceObject=display.newCircle(20,100,5)
referenceObject:setFillColor(0,255,0)
panelGroup:insert(panelBG)
panelGroup:insert(referenceObject)
 
-------------------
--drag function
-------------------
local function dragPanel( event )
        local t = event.target
    local phase = event.phase
    
    local highestDragPos = panelBG.contentHeight + display.contentHeight 
    local lowestDragPos = 0
    
    local initialTimeMsec = system.getTimer()
    local localEventX , localEventY = t.parent:contentToLocal(event.x,event.y)
    if "began" == phase then
                display.getCurrentStage():setFocus( t, event.id )
                t.isFocus = true
 
                -- Store initial position
                t.y0 = localEventY - t.y
                t.lastY = localEventY
                initialTimeMsec = system.getTimer()
    elseif t.isFocus then
                if "moved" == phase then
                
                local newY = localEventY - t.y0
                if t.y>newY then t.direction=-1 else t.direction=1 end
                print(t.direction)
                t.y = setToWithinLimits(newY,lowestDragPos,highestDragPos)
 
                elseif "ended" == phase or "cancelled" == phase then
                                -- calc speed
                                                local dT = system.getTimer() - initialTimeMsec
                                                
                                                local flickSpeed = t.direction*math.abs(((localEventY-t.lastY) / dT ))*.01
                                                local newYAfterAcelleration = setToWithinLimits((t.y+flickSpeed),lowestDragPos,highestDragPos)
                                                
                                                transition.to(t,{y=newYAfterAcelleration,transition=easing.outExpo})
                
                        display.getCurrentStage():setFocus( t, nil )
                        t.isFocus = false
                end
        end
        return true
end
 
panelGroup:addEventListener("touch",dragPanel)

views:1795 update：2011/10/15 21:01:16


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