Itempools Guide

[MindWorX]

This is a tutorial I decided to make, because from what i've experienced, very few people actually know about the itempool natives, and even fewer knows how to use them.

Itempools are an internal system, just like a normal units droptable, you know, the ones where you doubleclick a unit, and sets it's droptable.

Short explanation of the natives:

//Creates an itempool.
native CreateItemPool           takes nothing returns itempool

//Destroys an itempool.
native DestroyItemPool          takes itempool whichItemPool returns nothing

//Adds an item to an itempool.
native ItemPoolAddItemType      takes itempool whichItemPool, integer itemId, real weight returns nothing

//Removes an item from an itempool.
native ItemPoolRemoveItemType   takes itempool whichItemPool, integer itemId returns nothing

//Creates a random item from an itempool.
native PlaceRandomItem          takes itempool whichItemPool, real x, real y returns item

That's the natives from Common.j.

Here's some examples:
This creates an item pool, with 1/2(50%) chance of dropping item 'I001' and 1/2(50%) chance of dropping item 'I002'.

 local itempool ip = CreateItemPool()
    call ItemPoolAddItemType(ip, 'I001', 1)
    call ItemPoolAddItemType(ip, 'I002', 1)

This creates an item pool, with 1/3(33%) chance of dropping item 'I001' and 2/3(66%) chance of dropping item 'I002'.

 local itempool ip = CreateItemPool()
    call ItemPoolAddItemType(ip, 'I001', 1)
    call ItemPoolAddItemType(ip, 'I002', 2)

This creates an item pool, with 1/5(20%) chance of dropping item 'I001', 2/5(40%) chance of dropping item 'I002' and 2/5(40%) chance of dropping item 'I003'.

 local itempool ip = CreateItemPool()
    call ItemPoolAddItemType(ip, 'I001', 1)
    call ItemPoolAddItemType(ip, 'I002', 2)
    call ItemPoolAddItemType(ip, 'I003', 2)

As you can see it's pretty simple actually, the "weight" determines the chance of how often an item will drop. The easiest way to get the drop chance of an itempool, is to add the weight's together and divide the individual weight. Like the last example there's 1+2+2 which is 5, then 'I001' has 1 as weight, then you just do 1/5 which is 0.20, then you multiply by 100, and you have 20%.

To create an item using an itempool, you just use the PlaceRandomItem native, like this:

 local itempool ip = CreateItemPool()
    call ItemPoolAddItemType(ip, 'I001', 1)
    call ItemPoolAddItemType(ip, 'I002', 2)
    call ItemPoolAddItemType(ip, 'I003', 2)
    call PlaceRandomItem(ip,x,y)

This will place a random item from the itempool created, and return the item created, incase you want to do something with it.

An example of using the returned item would be the following function i use in hero rewards:

function GiveUnitRandomItem takes unit u, itempool ip returns nothing
 local item i = PlaceRandomItem(ip,0,0)
    call UnitAddItem(u,ip)
    set i = null
endfunction

Leaks: You should always remember to destroy itempools that you don't use. And also, remember to null any itempool variabels after you're done using them.

Hope this tutorial helps someone understanding itempools.

- MindWorX

 

[PurgeandFire]

Short but good tutorial. It is descriptive as well. This tutorial actually gave me an understanding of JASS itempools. Gj and +rep!

 

[Dr Super Good]

Only reason I see this not being approved is that it has no demo map showing how to use it to make a basic system, but next to that this should definatly be approved. Also you should add a warning that they can leak unless you destroy them if you use them only once as a local.

 

[MindWorX]

Only reason I see this not being approved is that it has no demo map showing how to use it to make a basic system, but next to that this should definatly be approved. Also you should add a warning that they can leak unless you destroy them if you use them only once as a local.

Done and Done.

 

[Wolverabid]

Tutorial Approved!

~ Thread moved to JASS/AI Scripts Tutorials.

 

[Tasyen]

One can add a nothing roll to an itempool by using 0 as itemCode in ItemPoolAddItemType(ip, 0, 1).