How to have a car driving off screen

flyhere · February 2014

Sorry if this is basic, but I spent a couple of hours looking and still couldn't find the answer.

I want to have a car moving along and going off the screen, and of course it came from off screen into play. Just like traffic passing by. I used MovieClip to get the tweening but that's for animation within the frame, how to get the continuous traffic coming into the screen and going off the screen?

I don't want to use some kind of endless moving background, as my other characters are static within my frame.

Thanks

flyhere · February 2014

I played around a bit more, and I think I found the answer.

kredor7 · February 2014

You can try using Gtween

http://appcodingeasy.com/Gideros-Mobile/Gideros-GTween-with-easing

In short if you set your objects position off screen first and then set up a tween to a position on the other side of the screen this should work fine.

thanhquan1512 · February 2014

In my experience, I used onEnterframe event to control object position. Create a car (bitmap or movieClip) at left center of the screen then move from left to right like below:

local function runGame()
       car:setX(car:getX() + CAR_SPEED)
end
stage:addEventListener(Event.ENTER_FRAME, runGame)

If you want more details answer, just ask. I will post tonight.

flyhere · February 2014

Thanks, that's exactly what I did. I use movieclip to position the car off frame, then play the movie clip to the other side (also off screen), and that worked fine.

My current problem is I want to loop thru and randomly generate a new car, trying to detect when a car has gone off the frame before spawning a new car. I either only spawn 1 car or too many cars at the same time.

It's a simple game with random car traffic running pass and the hero has to avoid collision, but I want no more than 2 cars (or max # of cars) in the frame.

@kredor7: Thanks, I'll take a look at Gtween, may use it for something else.
@thanhquan1512: I like your simple logic, will try it, detecting car going off frame when X coord is beyond the display frame. Then randomly spawn another car.

Thanks
Phi

OZApps · February 2014

local _W = SCREEN_WIDTH
local _xPos = car:getX()
local CAR_SPEED = 4 -- adjust for your speed and liking
 
if _xPos > _W then 
  --Car is off the screen
  -- either reposition this one of spawn a new one
  car:setX(-car:getWidth()) -- this will wrap the car off the right to the left
else 
  car:setX(xPos + CAR_SPEED)
end

if you want more, pull a random number and after those many frames have passed, spawn another car, when you spawn a new car, increase the number of cars by 1 and when the car goes off screen, decrease the number by 1. That way you can track the number of cars on screen at any given moment. Place the cars into an array rather than have variables like car1, car2, car3 and so on

Here are some articles I had written long long ago on starting out with game development

http://howto.oz-apps.com/2011/08/designing-game-movement.html
http://howto.oz-apps.com/2011/09/referencing-multiple-objects-of-same.html
http://howto.oz-apps.com/2011/09/creating-dynamic-variables.html

Some more that could help (written for another Lua Framework, but principles are the same)
http://howto.oz-apps.com/2011/09/scopes-for-functions.html
http://howto.oz-apps.com/2011/09/function-scope-answers.html
http://howto.oz-apps.com/2011/09/how-to-change-event-handlers-without.html

Plus there are many more articles if you scroll down on the page.

thanhquan1512 · February 2014

Try this:

local grpCar = Sprite.new()
local spawnCar() --check to spawn car every 1 second
     if frameCount % 60 == 0 and grpCar:getNumOfChilren() < 2 then
          local car = createCar(carX, carY)  --write a func to create a car at x=0, y = math.random(0, application:getContentHeight)
          grpCar:addChild(car)
     end
end
 
local function moveCar()
     car:setX(car:getX() + CAR_SPEED)
     if car:getX() > application:getContentWidth then
          car:removeFromParent()
          car = nil
     end
end
 
local function runGame()
     frameCount = frameCount + 1
     moveCar()
     spawnCar()
end
 
stage:addEventListener(Event.ENTER_FRAME, runGame)

flyhere · February 2014

Many thanks. Will try.

flyhere · February 2014

OZApps, thanhquan1512: I ended up not using your codes, but I got enough ideas from you to make it work with MovieClip.

Many thanks for your help.

OZApps · February 2014

@flyhere, cool as long as you got it working

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