bump.lua - minimal collision detection lib

[Roland_Yonaba]

Well that won't work. Let's see, if an item doesn't have a getBBox function, it will error, not just that, if it does, only the first return value will get used, and the rest will be item.t, w and h.

Sorry, you're totally right about the err, if item doesn't have a getBBox function.
The correct version will be:

Code: Select all

-- (Overridable) Given an item, return its bounding box (l,t,w,h)
function bump.getBBox(item)
  return item.getBBox and (item:getBBox()) or item.l, item.t, item.w, item.h
end

Actually it will work - I tried it - because everywhere in bump's code where getBBox is invoked (line 183), it is supposed to return 4 args. :

Code: Select all

  -- if the new bounding box is different from the stored one
  local l,t,w,h = bump.getBBox(item)

[Puzzlem00n]

The correct version will be:

Code: Select all

-- (Overridable) Given an item, return its bounding box (l,t,w,h)
function bump.getBBox(item)
  return item.getBBox and (item:getBBox()) or item.l, item.t, item.w, item.h
end

Ah, thanks a lot! Kikito, you should consider putting something like that in the master copy.

[kikito]

Code: Select all

-- (Overridable) Given an item, return its bounding box (l,t,w,h)
function bump.getBBox(item)
  return item.getBBox and (item:getBBox()) or item.l, item.t, item.w, item.h
end

You don't need item:getBBox(). That was just an example implementation. If your items don't have a :getBBox method, it is fine to do this (adapt to however your items return a bounding box):

Code: Select all

function bump.getBBox(item)
  return item.l, item.t, item.w, item.h
end

[Puzzlem00n]

You don't need item:getBBox(). That was just an example implementation. If your items don't have a :getBBox method, it is fine to do this (adapt to however your items return a bounding box:

Code: Select all

function bump.getBBox(item)
  return item.l, item.t, item.w, item.h
end

Oh, alright then. Even better.

I feel that the majority of my comments on this library have been negative, so I'll take this opportunity to say that I do appreciate your work on it and as soon as I get it working I'm sure it'll become very useful in the future!

[bartbes]

Code: Select all

-- (Overridable) Given an item, return its bounding box (l,t,w,h)
function bump.getBBox(item)
  return item.getBBox and (item:getBBox()) or item.l, item.t, item.w, item.h
end

Nope, still won't work, the ternary doesn't work quite right with multiple return values, in this case it returns
((item:getBBox()) or item.l), item.t, item.w, item.h

Actually, your parentheses only make it worse (not that it will work without them), because they force only the first return value to be used.

[Roland_Yonaba]

@bartbes:
Let's say, that I have, for instance :

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obj  = { a = 1, b = 2, c = 3, d  =4 }
function obj:out() return self.a,self.b,self.c,self.d end

function out(i)
	return i.out and (i:out()) or i.a, i.b, i.c, i.d
end

local a,b,c,d = out(obj)
print(a,b,c,d) --> 1, 2, 3, 4
obj.out = nil
a,b,c,d = out(obj)
print(a,b,c,d) --> 1, 2, 3, 4

So, what did I missed ?

@kikito: sorry for being off-topic, but I needed to understand bartbes' point.

[bartbes]

So, what did I missed ?

That your code only works because the names happen to be the same:

Code: Select all

Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
> obj = { w = 1, x = 2, y = 3, z = 4 }
> function obj:out() return self.w, self.x, self.y, self.z end
> function out(i)
>> return i.out and (i:out()) or i.a, i.b, i.c, i.d
>> end
> print(out(obj))
1	nil	nil	nil

[Roland_Yonaba]

That your code only works because the names happen to be the same

And yes, I got your point.
Actually, an if-return-else-return-end works fine. Thanks pointing that out.

[kikito]

Hi,

I am back from my holidays. I did the "simplified demo" that Puzzlem00n was requesting some time ago. It has its own branch on github now:

https://github.com/kikito/bump.lua/tree/simpledemo

I'm also attaching the .love file here:

bump-simpledemo.love

(7.36 KiB) Downloaded 214 times

This is probably not needed any more, but it was a good exercise after 3 weeks not touching any code

[tilmah]

Hi Kikito,
To remove all static objects in Bump, can you simply make a huge selection. For example the width and height of the screen (perhaps 800 by 600)?

Anyway... I am trying to hack a one way platform system using ATL and Bump.

I found a way of getting the information of a layer of tiles and adding static objects in bump in their place when the character jumps/reaches a certain height on screen, but I can't seem to do the reverse in removing them when the character goes below that height.

It worked when used a 'static' table into Bump. So it seems plausible.

Any suggestions would be appreciated.

Again thanks for your libraries.
p.s. Why do you have 't' and 'l' in Bump instead of 'x' and 'y'? What do they stand for?