Trouble with Movement of Physics Objects

Questions
1

Hey, I’m having trouble with moving my physics objects stated in the setup function. There are tabs of code missing, but none of them are important in this case.


-- Neon Air Hockey

-- Main

supportedOrientations(PORTRAIT_ANY)
displayMode(OVERLAY)
rectMode(RADIUS)
ellipseMode(RADIUS)

function setup()
    
    print("Pong")
    
    -- Menu
    menu = true
    
    -- Button
    button = Images:getButton()
    buttonStart = Button("Start",WIDTH/2,HEIGHT/5*2,350,150,100,0,255,0,button,menuOff)
    
    -- Ball
    ball = physics.body(CIRCLE,25)
    ball.type = DYNAMIC
    ball.x = WIDTH/2
    ball.y = HEIGHT/2
    ball.gravityScale = 0
    ball.sleepingAllowed = false
    
    -- variables for Player 1 and 2 paddles
    pos1 = vec2(WIDTH/2, HEIGHT/4)
    pos2 = vec2(WIDTH/2, HEIGHT/4*3)
    steer1 = vec2(0,0)
    steer2 = vec2(0,0)
    speed = 1600
    
    -- Player 1's Controller
    controller1 = VirtualStick {
    moved = function(v) steer1 = v end,
    released = function(v) steer1 = vec2(0,0) end,
    x0=0,x1=1,y0=0,y1=0.25,name="Player 1",nameSide="right"}
    
    -- Player 1's Paddle
    Player1 = physics.body(CIRCLE,50)
    Player1.type = KINEMATIC
    Player1.x = pos1.x
    Player1.y = pos1.y
    Player1.gravityScale = 0
    Player1.sleepingAllowed = false
    
    -- Player 2's Controller
    controller2 = VirtualStick {
    moved = function(v) steer2 = v end,
    released = function(v) steer2 = vec2(0,0) end,
    x0=0,x1=1,y0=0.75,y1=1,name="Player 2",nameSide="left",orientation="back"}
    
    -- Player 2's Paddle
    Player2 = physics.body(CIRCLE,50)
    Player2.type = KINEMATIC
    Player2.x = pos2.x
    Player2.y = pos2.y
    Player2.gravityScale = 0
    Player2.sleepingAllowed = false
    
    allControllers = All({controller1,controller2})
    
end

function touched(touch)

allControllers:touched(touch)

end

function draw()
    
    background(15, 15, 15, 255)
    
    if menu == true then
        drawMenu()
        buttonStart:draw()
        else
        
        pushStyle()
        strokeWidth(10)
        stroke(0, 255, 0, 255)
        lineCapMode(SQUARE)
        line(0,HEIGHT/2,WIDTH,HEIGHT/2)
        strokeWidth(20)
        fill(0, 0, 0, 0)
        rect(WIDTH/2,HEIGHT/2,WIDTH/2,HEIGHT/2)
        popStyle()
        
        -- Ball
        ellipse(ball.x,ball.y,25)
        
        -- Player 1
        pos1 = pos1 + steer1*speed*DeltaTime
        pos1.x = math.max(0,pos1.x)
        pos1.x = math.min(WIDTH,pos1.x)
        pos1.y = math.max(0,pos1.y)
        pos1.y = math.min(HEIGHT/2,pos1.y)
        fill(255,0,0,255)
        ellipse(Player1.x, Player1.y, 50)
        
        -- Player 2
        pos2 = pos2 + steer2*speed*DeltaTime
        pos2.x = math.max(0,pos2.x)
        pos2.x = math.min(WIDTH,pos2.x)
        pos2.y = math.max(HEIGHT/2,pos2.y)
        pos2.y = math.min(HEIGHT,pos2.y)
        fill(0,255,255,255)
        ellipse(Player2.x, Player2.y, 50)
        
        
        allControllers:draw()
        
    end
    
end

There are 3 physics objects, and 2 of them would be moved by my virtual controller sticks. These controllers work fine on moving sprites by the 2D vectors ‘pos1’ and ‘pos2’. However, these don’t seem to apply to the kinematic circles named ‘Player1’ and ‘Player2’.

The physics lines corresponding to these physics objects are under ‘-- Player 1’s Paddle’ and ‘-- Player 2’s Paddle’.

Please help.

2

Also, the grey boxes containing the code are being formatted weirdly, unless I’m not quite using them right.

3

You nearly had the code formatting right, use three ~

Actually, the missing code could be important, because none of the code above changes the positions of Player1 and Player2…

4

Simply put, the positions are changed like this:

  • pos (1 or 2) is the starting position.
  • steer is the vector direction that changes as the controllers receive information on which way to change. Steer directs which way the object moves (a sprite worked before with this)
  • the speed is just how many pixels the object moves per second (i think)

Because I know that all the position work on the other tabs is correct, and all physics work is done on this tab only, the rest should not matter, unless you want to know exactly how it changes the movement.

EDIT - The ball, I think, should move as planned, but with no way to move the paddles (player1 and player2) I am not ale to test it out.

5

The paddles are kinematic objects, which are not affected by gravity, only by your changing their positions in code.

That does not happen in the code above. If you have code that does change the paddle positions, please post it. (If you don’t have that code, there is your problem).

6

I’m sorry, I mis-posted the explanation about the code. You see, I said that pos1 and pos2 were the starting positions. What I failed to mention was that pos1 and pos2 are variables that start out as the starting position, bu are changed by steer, speed, and deltaTime to produce a change of a position in x and y. In short, they actually ARE changing the position, or they should…
Is that sufficient for you to work out why the paddles are not moving?

7

Ah, I see.

Your problem may be that when you say (in setup) Player1.x = pos1.x, that makes Player1.x equal to whatever is in pos.x, but won’t update it for changes in pos.x.

The way to make it update automatically is to write this instead in setup

Player1.pos=pos

Now, because you are assigning something more complicated (a vec2) than a number or text, to a variable, Codea will store the address of pos, not the hard coded value, and this means Player.pos will be linked to pos and update when it changes.

(If you do this, you will need to change any code that used Player1.x and Player1.y to use Player1.pos.x and Player1.pos.y instead).

Let me know if unclear.

8

Just to make sure -

Recap: Change the .x and the .y to object.position, because .position is for vec2.

Correct?

9

no, the name for a vec2 can be anything, but pos or position is a good choice.

Previously you said Player1.x=pos1.x

We can’t replace that with Player1=pos1, obviously, we need to create a property under Player1, so I simply called it pos

10

The key change is assigning a vec2 to the Player1 position variable, so Codea stores an address (of pos1), and not just a fixed number.

11

I see, but I tried what you said anyway, and it has not worked yet. I’ll see if there is anything I missed, but…

EDIT - does it need to be in the draw function, or should it still be in setup()?

12

Try this little app (add a new tab to the right,put it there and run). And no, this code doesn’t need to be in draw, setup is the right place.

(In your code, make sure you have changed all previous references to Player1.x and Player1.y)

function setup()
    pos1=vec2(100,200)
    --your code
    Player1={}
    Player1.x=pos1.x
    Player1.y=pos1.y
    --my code
    Player1A={}
    Player1A.pos=pos1
    --change pos1
    pos1.x=500
    --print results
    print("pos=",pos1.x,pos1.y)
    print("yours=",Player1.x,Player1.y)
    print("mine=",Player1A.pos.x,Player1A.pos.y)
end

function draw() end
13

I just experimentally moved the object.pos = pos lines into the draw function, seems they now work! Thanks for your support, Ignatz!

14

I’ll still try your tab to see if there is any difference there.

15

It made the screen black, literally.

16

results=

Output
pos= 500 200
yours= 100 200
mine= 500 200

17

oh well, as long as it works now

18

Thanks for your support though, Ignatz, the .pos worked wonders.

19

@CayDay47 - I realised the reason you got a black screen running my code was you must have made your app full screen, and my printing out was hidden

If you put this line at the top of my code displayMode(STANDARD) you should see that my solution fixes your problem

If you haven’t come across memory pointers before, try this

http://coolcodea.wordpress.com/2013/06/14/84-tables-and-pointers/

20

Was this what happened when you said,

Now, because you are assigning something more complicated (a vec2) than a
number or text, to a variable, Codea will store the address of pos, not the hard
coded value, and this means Player.pos will be linked to pos and update when it
changes.