How should I handle collision using setSpritePosition?

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Kobaltic

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Posted: 22nd Sep 2012 07:11

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I use setSpritePosition to move my player around. I have a ton of walls and want collision. Using setSpritePhysicsOn doesn't work when you use setSpritePosition. I can do a simple collision check but I am not sure how to do this to test all the walls in the level. I don't want to make several hundred checks each loop. Thanks in advance.

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Hodgey

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Posted: 22nd Sep 2012 08:14

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Quote: "I can do a simple collision check but I am not sure how to do this to test all the walls in the level. I don't want to make several hundred checks each loop. "

You'll have to perform some sort of check against each wall (unless you've set up your program in such a way that it doesn't need collision detection e.g tiles). You could do a distance check to narrow it down but you'll still have to check each wall (either distance or collision). You can also check for collision every x amount of milliseconds.

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baxslash

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Posted: 22nd Sep 2012 09:06

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You could put all your walls in a particular group using setSpriteGroup and then rayCastGroup around your player to see what is around him.

Another way would be to set your character up as a physics sprite and let box2d take care of collisions for you...

this.mess = abs(sin(times#))

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Kobaltic

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Posted: 22nd Sep 2012 20:44

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Quote: "Another way would be to set your character up as a physics sprite and let box2d take care of collisions for you..."

I have physics on both the walls and my player. The problem is that setSpritePosition overrides the physics.

Maybe I could move the player in a different fashion to allow box2d to work. Right now when you click a button (such as up, left, right, or down) I run through a small loop increasing the movement by .25 until it reaches a total movement of 10%.

Here is my movement code for north or up.

+ Code Snippet

function north()

        playSprite (SMW, 15,1, 9,16)
       do
        if newY# > currentY# - 8
            newY# = newY# - .20
        setSpritePosition(SMW, newX#, newY#)
        else
        stopSprite(SMW)
        exit
        endif

sync()
loop
endfunction

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Ancient Lady

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Posted: 22nd Sep 2012 21:20

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I use the SetSpritePhysicsImpulse command to move my player. It lets you set a direction and speed and then the physics takes over.

Decide what you want the x/y direction is and how fast and then something like this:

+ Code Snippet

vX = <some x direction> * <some x speed>
vY = <some y direction> * <some y speed>
currX = GetSpriteXByOffset(spriteid) // assumes you set the offset at center of sprite
currY = GetSpriteYByOffset(spriteid)
SetSpritePhysicsImpulse(spriteid,currX,currY,vX,Vy)

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Ancient Lady
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baxslash

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Posted: 22nd Sep 2012 22:43

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Impulse works but I tend to use velocity as it's easier to control. Impulse keeps building and building whereas velocity is a set speed and your player still reacts to other objects.

this.mess = abs(sin(times#))

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Ancient Lady

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Posted: 23rd Sep 2012 01:25

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The same code works with velocity, just don't worry about the current position. It reacts much faster.

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Ancient Lady
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Kobaltic

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Posted: 24th Sep 2012 19:54

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I got velocity to work but still having problems with physics not working. If I set the wall to physicsOn 2, then I can push the wall around. Any other setting and I walk right through it.

Here is my character code

+ Code Snippet


SMWI = loadimage ("walkingSwordMan.png") //SMWI swordManWalking Image
    SMW = createSprite (SMWI)
    setSpriteSize(SMW, 20, -1)
    setSpritePosition (SMW, 50,60)
    setSpriteDepth(SMW, 5)
    setSpriteAnimation(SMW,96,96,64 )
    setSpriteShape(SMW,3)
    setSpritePhysicsOn(SMW, 3)
    playSprite(SMW, 15,0,9,9)
    stopSprite(SMW)

Here is the code for my wall

+ Code Snippet

wall1 = CreateSprite ( wall1 )
    SetSpriteSize ( wall1 , 20 , -1 )
    setSpritePosition (wall1,50,50)
    setSpriteDepth (wall1,5)
    setSpriteShape(wall1, 2)
    setSpritePhysicsOn (wall1, 3)

Here is the check to see which button is pushed

+ Code Snippet

if (  getPointerPressed ()= 1)
    dir =  getSpriteHit (getPointerX (), getPointerY ())
        if dir = bNorth

             north()
        elseif dir = bEast
             east()
        elseif dir = bSouth
             south()
        elseif dir = bWest
             west()
        elseif dir = bNW
             NW()
        elseif dir = bNE
             NE()
        elseif dir = bSW
             SW()
        elseif dir = bSE
             SE()
      remstart
        elseif dir = bTurn
        if n > 56
            n = 1
        endif
        n = n + 7
    playSprite(SMW, 15,0,n,n)
    stopSprite(SMW)
    remend
    endif

Here is the new movement and animation code

+ Code Snippet

 function north()
    SetSpritePhysicsVelocity(SMW,0,negY# )
    playSprite (SMW, 15,1, 9,16)

    newY#=negY#

 do
        if newY# < negY# + 10
            newY# = newY# + .20

        else
            SetSpritePhysicsVelocity(SMW,0,0 )
            stopSprite(SMW)
            exit
        endif

sync()
loop

endfunction

Two things. I am not sure how to stop the velocity so I set it to 0,0. Also I am not sure if the collision isn't picking up do to the loop I am running inside the function.

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Ancient Lady

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Posted: 24th Sep 2012 20:54

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Your player should be dynamic: setSpritePhysicsOn(SMW, 2)

Do you want the wall to move? If not, make it static: setSpritePhysicsOn (wall1, 1)

Do you want your player to stop when they reach a wall or bounce?

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Ancient Lady
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Ancient Lady

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Posted: 24th Sep 2012 20:56

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And I don't really see what you are accomplishing with the do loop in your function. It looks like it just adjusts a value until it reaches some value and then you stop the player. This is definitely killing your collision.

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Ancient Lady
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Kobaltic

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Posted: 24th Sep 2012 21:10 Edited at: 24th Sep 2012 21:11

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OK I set the player physics to 2 and gravity to 0,0. Now the collision works but the player now spins when he hits the wall.

How should I stop the velocity? I was moving him in the loop and then using the number to determine the stopping point to stop the velocity and stop the animation.

edit: I want the player to stop when he hits the wall.

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Ancient Lady

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Posted: 24th Sep 2012 22:09

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Do you always want to stop the player when it hits an object?

If so, you can check for collision with a wall each main loop (take the loops out of your north(), NW(), etc. functions, they aren't doing anything useful) and stop if there is a collision.

Here is some sample code based on yours:

// all your setup stuff

// main loop
do
  // check for collision, assumes wall is what we hit
  icnt = GetSpriteFirstContact(SMW)
  if (icnt > 0)
    // you might want to check if icnt is same as one of your
    // wall objects in here as well
    SetSpritePhysicsVelocity(SMW,0,0)
    StopSprite(SMW)
  endif

// check for pointer pressed
  if (GetPointerPressed())
    dir = GetSpriteHit(GetPointerX(),GetPointerY())
    select dir
      case bNorth
        north()
      endcase
      case bEast
        east()
      endcase
      case bSouth
        south()
      endcase
      case bWest
        west()
      endcase
      case bNW
        NW()
      endcase
      case bNE
        NE()
      endcase
      case bSW
        SW()
      endcase
      case bSE
        SE()
      endcase
      case default
        // maybe you do something
      endcase
    endselect
  endif
loop

// do the same for the other functions as this one
function north()
  SetSpritePhysicsVelocity(SMW,0,negY#)
  playSprite (SMW, 15,1, 9,16)
endfunction

+ Code Snippet

// all your setup stuff

// main loop
do
  // check for collision, assumes wall is what we hit
  icnt = GetSpriteFirstContact(SMW)
  if (icnt > 0)
    // you might want to check if icnt is same as one of your
    // wall objects in here as well
    SetSpritePhysicsVelocity(SMW,0,0)
    StopSprite(SMW)
  endif

  // check for pointer pressed
  if (GetPointerPressed())
    dir = GetSpriteHit(GetPointerX(),GetPointerY())
    select dir
      case bNorth
        north()
      endcase
      case bEast
        east()
      endcase
      case bSouth
        south()
      endcase
      case bWest
        west()
      endcase
      case bNW
        NW()
      endcase
      case bNE
        NE()
      endcase
      case bSW
        SW()
      endcase
      case bSE
        SE()
      endcase
      case default
        // maybe you do something
      endcase
    endselect
  endif
loop

// do the same for the other functions as this one
function north()
  SetSpritePhysicsVelocity(SMW,0,negY#)
  playSprite (SMW, 15,1, 9,16)
endfunction

I might also suggest creating a UDT with x and y velocity and start and stop frames for each direction. Then make an array of them and initialise with all the values for each direction, use the 'dir' value (adjust the sprite ids and the returned value so that it matches the appropriate entry in the array). Then you can have one function that you pass an index and it handles the rest. And you would not not the select or if/elseif setup.

Cheers,
Ancient Lady
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Kobaltic

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Posted: 25th Sep 2012 20:00

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OK I got the collision working now. Thank goodness I didn't want to have to check every single wall individuality.

I used the loop in the functions to control the distance traveled. The player will roll a die and then move that many spaces. The loop determined how much distance to move for one space. Now I need a way to only allow one button push to move the player 10% of the Y axis and 12% of the X axis.

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Kobaltic

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Posted: 29th Sep 2012 06:24

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well, everything worked correctly. Until I walked off the screen and realized I need screen scrolling. So I added that in and now my collision is broken again. I can't even do a collision check. I printed out the collision to make sure it was working and nothing. If the screen is moving I have no collision. Is there a different collision command for a scrolling screen? Thanks again.

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baxslash

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Posted: 29th Sep 2012 11:23

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You might need to change screen co-ordinate a into world co-ordinate a using screenToWorldX and screenToWorldY?

this.mess = abs(sin(times#))

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Kobaltic

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Posted: 30th Sep 2012 07:13

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Ok well here is my code it. As far as I can tell it never checks for a collision.

definitions:

+ Code Snippet

//set the speed of the player  and direction
 posX# = 12
 negX# = -12
 posY# = 10
 negY# = -10

 currentX# =  GetViewOffsetX()
    currentY# =  GetViewOffsetY()
    newX# = currentX#
   newY# = currentY#

loop

do
icnt =  GetSpriteFirstContact(move) // check if we hit something
 print ("collision ="+ str (icnt))
  // if GetSpriteCollision ( move, wall1 ) = 1
    if (icnt > 0) //if we did hit something stop
            SetSpritePhysicsVelocity(move,0,.25) // back up just off the wall so we don't have collision right away on next move
        //SetSpritePhysicsAngularVelocity(move,0) // set this so our player doesn't spin from physics
        StopSprite(move) // stop the animation from playing
        setSpritePhysicsOff(move)// turn off physics so no collisions will move the player
     else
      setViewOffset( currentX#,  currentY#) //move the screen not the player
       if currentY# > currentY# + negY#// check grid distance
       currentY# = currentY# -.25// move on Y axis this number of units per frame, controls speed
       currentX# = currentX#      // move on x axis this number of units per frame, controls speed

endif

if currentY# = newY# +negY#

SetSpritePhysicsVelocity(move,0,0 )
            setSpritePhysicsOff(move)
            stopSprite(move)
            dice = dice - 1
            exit
        endif
endif

sync()
loop

+ Code Snippet

do
icnt =  GetSpriteFirstContact(move) // check if we hit something
 print ("collision ="+ str (icnt))
  // if GetSpriteCollision ( move, wall1 ) = 1
    if (icnt > 0) //if we did hit something stop
            SetSpritePhysicsVelocity(move,0,.25) // back up just off the wall so we don't have collision right away on next move
        //SetSpritePhysicsAngularVelocity(move,0) // set this so our player doesn't spin from physics
        StopSprite(move) // stop the animation from playing
        setSpritePhysicsOff(move)// turn off physics so no collisions will move the player
     else
      setViewOffset( currentX#,  currentY#) //move the screen not the player
       if currentY# > currentY# + negY#// check grid distance
       currentY# = currentY# -.25// move on Y axis this number of units per frame, controls speed
       currentX# = currentX#      // move on x axis this number of units per frame, controls speed

    endif

if currentY# = newY# +negY#

            SetSpritePhysicsVelocity(move,0,0 )
            setSpritePhysicsOff(move)
            stopSprite(move)
            dice = dice - 1
            exit
        endif
endif

sync()
loop

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Hodgey

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Posted: 30th Sep 2012 08:38

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I'm not sure about your collision but a small piece of programming advice: it's generally not a good idea to do an equality comparison between two floats.

E.g if currentY# = newY# +negY#

currentY# will rarely, if ever, be equal in the computer's eyes to newY# + negY#. It's best to cater for some small degree of variance.

A quick work around:

if abs(currentY# - (newY# + negY#)) < 0.2

Where 0.2 is the variance permitted (you can change this).

Cheers

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Kobaltic

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Posted: 30th Sep 2012 17:44

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Thanks. For the tip.

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Kobaltic

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Posted: 1st Oct 2012 18:04

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Ok I found my problem. It turns out that the collision sticks to the screen. When I move my view the sprite moves correctly but the collision seems to be fixedToScreen. So the collision is always the same distance from my player since my player is fixedToScreen. Any thoughts on how to get the collision to stay with the sprite it is assigned to?

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baxslash

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Posted: 1st Oct 2012 18:07

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The collision shape will only be fixed to the screen if the player sprite is also fixed using "fixSpriteToScreen". It's not really a good idea to use this for anything you want to interact with the rest of the "world".

this.mess = abs(sin(times#))

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Kobaltic

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Posted: 1st Oct 2012 18:15

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My wall collision is what seems to be fixed to screen. The wall itself is not. The wall moves correctly when I change my view offset but the wall's collision is fixed to the screen.

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baxslash

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Posted: 1st Oct 2012 18:19

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Try using "fixSpriteToScreen(wallSpriteID,0)", that should stop it from being fixed to the screen but it is set to zero by default so if that fixes the problem it must be set to one somewhere in your code.

this.mess = abs(sin(times#))

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Kobaltic

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Posted: 1st Oct 2012 18:36

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Didn't fix the problem. This is strange. I added a second wall and it does the exact same thing. I played around with the shape and the physicsOn options and nothing seems to be working.

Is there a way to place the wall in world coordinates?

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baxslash

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Posted: 1st Oct 2012 18:38

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When you position a sprite it is always in world co-ordinates unless you fix to screen.

Have you checked for that in your code? Maybe you could post something to debug?

this.mess = abs(sin(times#))

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Kobaltic

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Posted: 1st Oct 2012 18:55

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I uploaded my whole file. just put into the basic folder. I know my code is not clean and it isn't perfect.

I only have one call to the fixSpriteToScreen that is for (move) which really should say player.

How to move and test. First you need to hit the up arrow button in the middle of the screen to roll the dice. I fixed the dice to always give 10 moves for right now. The buttons on the left move the player, disregard the direction of the arrows I need to fix them. The position of the button will tell you the direction it moves. The middle button switches which character the player is controlling.

North and East buttons move the screen and you will see he walks through the wall. The other buttons only move the player. After you walk through the wall, use the NorthWest and NorthEast buttons to walk up and hit the collision from the wall.

password is abc

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baxslash

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Posted: 1st Oct 2012 19:17

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Yes, the player is being fixed to the screen:
FixSpriteToScreen(move, 1)

Your collision system seems to work if you don't set this.

this.mess = abs(sin(times#))

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Kobaltic

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Posted: 1st Oct 2012 19:30

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Yes that is true. The problem lies with the wall's collision. If the player is fixed to the screen the wall's collision shouldn't be.

Maybe I can move the player at the same speed that the scrolling is happening.

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Kobaltic

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Posted: 1st Oct 2012 19:38

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ok I turned off the fixSpriteToScreen for the player and now I am moving him when the screen scrolls. I just have to match the speed and I should be good.

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Kobaltic

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Posted: 1st Oct 2012 21:50

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Thanks Baxslash, I am all set moving perfect. Colliding perfect. All 8 directions working perfect. I have never been so happy to hit a wall.

Now I can work on updating the screen position when I switch characters. That should be fun.

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baxslash

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Posted: 1st Oct 2012 22:14

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Excellent! Looks like a fun project

this.mess = abs(sin(times#))

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AppGameKit Classic Chat / How should I handle collision using setSpritePosition?

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