About the inaccuracy in collision reports

Questions
1

Hi!

I’m dealing with collisions for some gameplay tests, and I think I’m getting to this point:

Touching: bool, whether or not the contact is currently touching. ***Due to the way contacts are cached this can be false under some circumstances***

(from the reference, about physics.contact)

Indeed, some contacts are left unreported. Not often, but often enough to make my little prototype frustrating. Is there a way to force the collide function to update itself in order to catch contacts it was previously ignoring?

Thanks!

2

Are you talking about problems with collisions (the collide function), or currently touching objects?

Also, are your objects moving fast? If so, you may need to turn bullet mode on.

3

That line in the reference just refers to the touching flag, not the collide function. I only use the collide function. If you need an isTouching flag, you can set it and clear it yourself on collide state began and ended.

A tip, if you don’t already use this method: have a table that indexes your game objects by their physics body.

In the class init:

Body = class() --master class for all physics bodies

bodies = {} --index instances of this class by their physics body

function Body:init()
    local bod = physics.body(CIRCLE, 10)
    bodies[bod] = self
end

Give the class a collide method:

function Body:collide(c, bod)
    if c.state == BEGAN then
        self.isTouching = true --flag for collision state
        if bodies[bod].category = categories.enemyBullet then --do some tests for what object has collided with
            --deduct some health
        end
    elseif c.state == ENDED then
        self.isTouching = false
    end
end

Then the global collide function just looks like this:

function collide(c)
    if bodies[c.bodyA] then bodies[c.bodyA]:collide(c, c.bodyB) end --pass the other body (the collide-ee) to the collide-er 
    if bodies[c.bodyB] then bodies[c.bodyB]:collide(c, c.bodyA) end
end
4

Hey, thanks to both of you! The objects were very slow, so it wasn’t the tunneling problem… But, I forced:

if contact.state == BEGAN then
    contact.bodyA.touching = true
    contact.bodyB.touching = true
end

if contact.state == END then
    contact.bodyA.touching = false
    contact.bodyB.touching = false
end

At the beginning of my collide(contact) function, and it seems to be working now!

I need to test it more, but the problem didn’t happen in a few minutes of gameplay. I’m really happy, thanks so much!

Now I need to fix that crazy Xcode issue so I can send it for review…

Cheers!

5

It should be ENDED not END

6

Oh yes, thanks!