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CoronaSDK 2012.741 | Released: 7 Feb 2012, 8:45am | What's New | Download Now

Time Animation

Features demonstrated:

Time-based animation.

Code:

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local screenW, screenH = display.contentWidth, display.contentHeight
local friction = 0.8
local gravity = .09
local speedX, speedY, prevX, prevY, lastTime, prevTime = 0, 0, 0, 0, 0, 0
 
local background = display.newImage( "metal_bg.png", true )
background.x = screenW / 2
background.y = screenH / 2
 
local infoLabel = display.newText( "Drag or fling ball to bounce", 0, 0, native.systemFontBold, 20 )
infoLabel:setTextColor( 0, 0, 0 )
infoLabel.x = screenW / 2
infoLabel.y = 60
 
local ball = display.newCircle( 0, 0, 40)
ball:setFillColor(255, 255, 255, 166)
ball.x = screenW * 0.5
ball.y = ball.height
 
function onMoveCircle(event) 
        local timePassed = event.time - lastTime
        lastTime = lastTime + timePassed
 
        speedY = speedY + gravity
 
        ball.x = ball.x + speedX*timePassed
        ball.y = ball.y + speedY*timePassed
 
        if ball.x >= screenW - ball.width*.5 then
                ball.x = screenW - ball.width*.5
                speedX = speedX*friction
                speedX = speedX*-1 --change direction     
        elseif ball.x <= ball.width*.5 then
            ball.x = ball.width*.5
                speedX = speedX*friction
                speedX = speedX*-1 --change direction     
        elseif ball.y >= screenH - ball.height*.5 then
                ball.y = screenH - ball.height*.5 
                speedY = speedY*friction
                speedX = speedX*friction
                speedY = speedY*-1  --change direction  
        elseif ball.y <= ball.height*.5 then
                ball.y = ball.height*.5
                speedY = speedY*friction
                speedY = speedY*-1 --change direction     
        end
end
        
-- A general function for dragging objects
local function startDrag( event )
        local t = event.target
        local phase = event.phase
 
        if "began" == phase then
                display.getCurrentStage():setFocus( t )
                t.isFocus = true
 
                -- Store initial position
                t.x0 = event.x - t.x
                t.y0 = event.y - t.y
                                                
                -- Stop current motion, if any
                Runtime:removeEventListener("enterFrame", onMoveCircle)
                -- Start tracking velocity
                Runtime:addEventListener("enterFrame", trackVelocity)
 
        elseif t.isFocus then
                if "moved" == phase then
                                        
                        t.x = event.x - t.x0
                        t.y = event.y - t.y0
 
                elseif "ended" == phase or "cancelled" == phase then
                        lastTime = event.time           
 
                        Runtime:removeEventListener("enterFrame", trackVelocity)
                        Runtime:addEventListener("enterFrame", onMoveCircle)
 
                        display.getCurrentStage():setFocus( nil )
                        t.isFocus = false
                end
        end
 
        -- Stop further propagation of touch event!
        return true
end
 
function trackVelocity(event) 
        local timePassed = event.time - prevTime
        prevTime = prevTime + timePassed
        
        speedX = (ball.x - prevX)/timePassed
        speedY = (ball.y - prevY)/timePassed
 
        prevX = ball.x
        prevY = ball.y
end                     
 
ball:addEventListener("touch", startDrag)
Runtime:addEventListener("enterFrame", onMoveCircle)