Interactions with Items

[Jake Style]

How do I make inventory items interact? I want to take one inventory item, put it ontop of another inventory item and they both dissapear and it creates a new inventory item which will be a combo of both.... Like, Water, And a cup... put them together, they dissapear and I now have a cup of water.

[Proskrito]

you have to make 3 inventory items: the empty cup, the water, and the cup filled with water.
Then, in the empty cup "use inventory item" interaction, you write something like:(suppose that empty cup is item #5, water is #6, and cup filled is #7)

if (player.activeinv==6){// if used water on cup
LoseInventory(5);
LoseInventory(6);
AddInventory(7);
}

and in the water interaction:

if (player.activeinv==5){//if used cup on water
LoseInventory(5);
LoseInventory(6);
AddInventory(7);
}