Sometimes physics bounds don't work

General
1

I have a chain that boxes in the game field. But sometimes objects, moving fast, can ignore the boundary and pass through it…how can I fix this?

2

See physics.continuous and “bullet” under physics.body in the reference.

3

@dave1707: thank you :slight_smile:

4

@dave1707 I’ve noticed in Codea 2.0 sometimes this doesn’t make a difference when using a chain body. It only happens when the game is below 35fps and I think it could be fixed by adding in more iterations, I haven’t tried this.

5

@Luatee I just tried a physics.body(CHAIN,…) and a physics.body(CIRCLE,0), (the smallest I could set the CIRCLE size). I set the linearVelocity of the CIRCLE to a velocity of 120 and the CIRCLE went thru the CHAIN. I then set physics.continuous=true and set the velocity to it max (3840) and the CIRCLE was stopped by the CHAIN each time. So it appears that physics.continuous works. I didn’t bother to set bullet to anything.

6

I’m operating at 160 velocity on the x, 0 on the y, radius of 1…hit or miss sometimes

7

@Invad3rZIM Without seeing the code it’s hard to say why it’s not working. In my test, I even set the CIRCLE size to 0 with a speed of 3840 and it was stopped by the CHAIN. I had physics.continuous=true in the setup() function.

8

@Invad3rZIM Are all of your velocities based on physics movement. If you move physics objects directly, then that causes problems.

9

@dave1707 yes, circles work flawlessly I know. But try this polygon:

local verts = {vec2(-9,0),vec2(-9,-4),vec2(-5,-6),vec2(0,-6),vec2(5,-6),vec2(9,-5),vec2(10,-3),vec2(10,3),vec2(7,6),vec2(4,5),vec2(2,4),vec2(-2,5),vec2(-6,4)}

And maybe more of a constant force on a jagged chain.
I’ve come to notice box2D has unreliable physics when using some sets of vertices, like a polygon rectangle with chamfered corners (45 degrees 16 pixel chamfer, total of 8 points) will cause bodies to pass through.

10

@Luatee I tried your verts on a POLYGON with a jagged CHAIN and it stops every time, even at max velocity. Maybe we’re doing thing differently.

11

@Luatee Here the code I was testing with.


displayMode(FULLSCREEN)
supportedOrientations(LANDSCAPE_ANY)

function setup()
    verts = {vec2(-9,0),vec2(-9,-4),vec2(-5,-6),
        vec2(0,-6),vec2(5,-6),vec2(9,-5),
        vec2(10,-3),vec2(10,3),vec2(7,6),
        vec2(4,5),vec2(2,4),vec2(-2,5),vec2(-6,4)}
    physics.continuous=true -- comment this and the chain wont stop the polygon
end

function setup1()
    maxVel=0
    if p then
        p:destroy()
        d:destroy()
    end
    p=physics.body(POLYGON,unpack(verts))
    p.x=0
    p.y=421
    p.gravityScale=0
    tab={}
    for z=1,50 do
        table.insert(tab,vec2(900+math.random(100),z*20-20))
    end
    d=physics.body(CHAIN,false,unpack(tab))
end

function draw()
    background(40,40,50)
    fill(255)
    stroke(255)
    strokeWidth(2)
    if p then
        for z=2,#tab do
            line(tab[z-1].x,tab[z-1].y,tab[z].x,tab[z].y)
        end
        i=#verts
        p:applyForce(vec2(200,0))
        for z=1,#verts do
            line(p.x+verts[i].x,p.y+verts[i].y,p.x+verts[z].x,p.y+verts[z].y)
            i=z            
        end
        maxVel=math.max(p.linearVelocity.x,maxVel)
        text("Velocity "..maxVel,WIDTH/2,HEIGHT-60)
        text("Max velocity is 3840",WIDTH/2,HEIGHT-30)
    end
    text("tap screen to start",WIDTH/2,HEIGHT-90)
end

function touched(t)
    if t.state==BEGAN then
        setup1()
    end
end
12

@dave1707 we are doing it differently, I’ve got a five second clip of the foot going through and it looks like it’s at where two points meet in the chain body, but I’m going to try a few other things

13

@Dave1707 mind if I pm you my code?

14

You can send it.