XNA Tile Based Collision

Question

I have a tile map of 64 x 64 pixel tiles (10 rows, 10 columns) I want to detect collision between the moving units and any walls or objects. How can i keep the units centered in the tile map while moving then detect if a unit should change direction without updating his position to soon, and throwing him off the center of the tile?

Example: If there is an object at TilePositionX = 3, and TilePosition = 0 and that object makes a unit change his direction but always stay centered. If the unit is heading right towards the object at a XVelocity = 1.0f (this could be any velocity) every update. Do i have to detect the center position of the unit then add an offset and check if I'm completely inside a tile? I can't of a good solution for my problem.

Answer 1

What I did in a similar situation was work out the target destination of the unit (in pixels) which was the centre of the tile it was moving toward, and then every update move the unit closer to that target. Only once the unit was in the centre of the tile did it check for a new destination.

For example: Unit A is at coordinates (0,0) which in pixels (32,32) (the centre of that tile) A moves toward tile (0,1), so new destination is (32,96). Every update the unit moves (0,1) pixels down. Once the unit is a (32,96) which is the centre of the tile (0,1), it can then decide where it is going to move next.

Answer 2

The way i handled this in a few of my games was i held a Tile and a Pixel offset, the Tile always stays a solid number I.E 1,2 and the pixel offset was moved negative positive based on direction. When it got above the size of a tile we would reset it to zero and add or subtract to the corrosponding Tile type. From there it becomes fairly easy to determine if you are hitting a tile that you cannot move on.