matamouros [Lexaloffle Blog Feed]

Maths for deflecting two objects off each other

Tue, 19 Jul 2022 17:08:54 UTC

Hi all, just a quick noob question. I'm struggling with making two objects (asteroids in this case) coming down a trajectory on x,y and colliding, deflect each other a little more realistically (but without having to implement a physics engine!). I don't have the maths skills as of yet, I'm guessing something to do with angles/trigonometry?

At the moment I'm basically forcing the leftmost asteroid to the left and the rightmost object to the right, but 90% of times this just looks very unnatural.

Would someone kindly point me some resource I could check up on/read/watch on how to approach this? I don't have the smarts to figure it out on my own, but will be more than ok researching it on my own - just need to be pointed in the right direction. Any tips or pointers would be greatly appreciated.

Thank you in advance!

Pedro.

Random bool

Sun, 26 Jun 2022 18:03:01 UTC

Aw man, I'm so sorry, I feel really silly... How on earth do you generate a random bool? I can't find any way to cast an int into a bool, so I'm down to doing the sort of stuff below:

randbool=flr(rnd(2))
if randbool==0 then randbool=false else randbool=true end

This feels really dirty and silly. What's the established way of doing this please? And apologies in advance.

Thanks,

Pedro.

Weird thing, can't catch zero anymore

Sun, 19 Jun 2022 11:45:16 UTC

Hi everyone, I think this can't be a bug that only I just found out so I'm posting it here for some help instead of in the bugs forum.

I seem to be having the weirdest behaviour easing out a negative var towards 0: it never becomes zero again (either negative or positive), despite printing as such. Check the below reproducer code and gif, neither y==0 nor y==-0 conditions catch the zero, even though at first you can see true.

Please help?

Thanks!

function _init()
 y=0
end

function _update()
 y*=0.85
 if btn(2) then
  y-=0.65
 end
end

function _draw()
 cls()
 print("time: "..time())
 print("y="..y)
 print("is y==0? "..(y==0 and 'true' or 'false'))
 print("is y==-0? "..(y==-0 and 'true' or 'false'))
end