I've got a project now that I'm creating sprites in but I'm having trouble finding the documentation for freeing up those slots and making them available to use again.
Okay that makes sense, I'm just a little worried about the memory that it would use since would the sprite data still be held in memory?
Also just so I don't have to make a new thread, can I still check collisions on a layer even if it isn't being drawn?
Don't worry by the memory. Each sprite takes about 100 bytes, so if you preallocate 128 sprites (SNES for example) it just takes about 13 kbytes. Nothing to worry about! Disabled sprites are free as they don't take any CPU cycles.
Yes, to check collisions with a given layer you must interrogate the layer tiles with
TLN_GetLayerTile():
http://www.tilengine.org/doc/md_layers.h...totoc_md47
This just requires having the layer loaded with a valid tileset and tilemap, but it will work even if you've disabled the layer with
TLN_DisableLayer() so it is not drawn.