Is caching tiles like this a good idea?

Question

I have a 2d int array which represents tiles on level like this:

0000000000000000000000
0000000000000000000000
0000000000000000000000
1111111111111111111111

I have a tileset vector, where each element has it's own tileX and tileY value(position of a tile in a tileset image), collision data etc. So, when I draw a level each time I draw a tile, I ask about them like this:

draw(tileset[currentTile]->tx, tileset[currentTile]->tY, tileWidth, tileHeight);

But, as you can see, there will be lots of the same elements when I iterate through for loop, so do I need to keep lastCollisionData variable in level class to reduce time used to access each tile separately?

Answer 1

Depending on how many times you need to traverse the list, as well as how big it will be in the long run, using something such as run length encoding could be valuable, but you have to consider the time required to encode the tiles each time there is a change to it. This is a situation where the trade off of more time spent up front, could increase performance during actual usage. If the performance hit is insignificant though, then it may not be necessary at all.

edit run length encoding is a process for identifying multiple values of the same time within a single run. For instance, rather than representing 00000000 as so, it could be represented as 80, where 8 represents the number, and 0 the value. Of course this takes time up front to perform the encoding, and may not save you time depending on how you are using the data.

http://en.wikipedia.org/wiki/Run-length_encoding