Tile map collision and object handling

Question

I want to program a game. In this game there is a tile map and objects that interact with it and them self.

For that I made first a TileMap class, in it is only the data of the tile map. Its a very simple tile map without layers and a tile have only and integer id.

Secondly I have a class TileMapRenderer that draws the map. It iterate threw all tiles and draw them dependent on there id.

So now I don't know how I can go further. How I handle different objects like players, animals, table, chests and let them "clean" interact with the tile map..... Has someone a idea?

And at last another problem with collision. [URL=http://www.directupload.net][IMG]http://s1.directupload.net/images/140303/q2n5ebsm.png[/IMG][/URL] If in this example the speed is smaller than 48, its perfect but if it bigger than 48 there is a problem. Because normally I check whether on the new Position (current position + velocity) would be a collision and if yes put it a tile before. But in a second case the player would be glitch threw on tile. How I should handle collision in relationship to a object system.

I hope there is someone how know a good solution.

Answer 1

I suggest to keep a tile as simple as possible, like you do with only giving it an ID, perhaps a bool for collision or any other simple things to identify what type of tile this represents. A class like this should look like, (All pseudo code, i'm a C# guy but implementing this in java should be a breeze if you know the basics):

class Tile
{
    public int baseID;
    public bool Collision;
}

This is pretty much all you need to draw everything necessary and have collision working. You just build layers of these in this order from back to front from left to right from top to bottom. (It does not need to be in this order if every sprite fits within the tilesize.)

Tile[,] baseMap = new Tile[100,100]; //Put in all your backgrounds
Tile[,] objectLayer = new Tile[100,100]; //Put in all your objects
Tile[,] anotherObjectLayer = new Tile[100,100]; //Put more objects in a separate layer.

You would draw it like this:

for (int y = 0; y < mapheight; y++)
{
    for (int x = 0; x < mapwidth; x++)
    {
        draw(baseMap[x,y]); //Obviously you need your implementation of ID to texture here.
//If your tiles are 32*32 you would draw it on x*32, y*32, width 32, height 32.
        draw(objectLayer[x,y]);
        draw(anotherObjectLayer[x,y]);
//Drawing it like this will result higher/further tiles to be covered by larger objects like tree's. 
//You need to find out where the moving things are, like the player, to draw them on the correct [x,y] iteration.
    }
}

If you need slightly different variables and parameters for a layer you are free to create another class for these. Maybe inheriting from the base tile class will do you good. Here is an example for a chest tile:

class Chest : Tile
{
    //The baseID would be it's texture.
    //The Collision can be used to have hidden chest or buried treasure.
    int ChestItemID; //The item ID this chest holds.
    List<int> MultipleItems; //For loot frenzy.
    bool MonsterInABox; //For oldschool feeling
    int Lock; //First get the key with this ID to unlock it.
}

Since this class inherits from tile it is perfectly fine to put this in one of the above layers so you do not have to create a complete layer arrays just for chests.

Next time make a new question for the collision issue since it is so different. Anyway, you glitch true since your tiles are probably 48*48 and this your character never steps on the tile with the collision on it. Therefor you should write a method that predicts what tiles your crossing. Depending on your needs you can check every pixel or just one step in between. Another option would be to calculate the next tile the player goes to remembering the first, with a tilemap like this it is very simple to check which tiles have been crossed between those points. First ask yourself if you need to move at speeds larger then your tiles, and what would be the maximum speed? If you just use the fast moving for debugging create a debug method for it.

Answer 2

From what I can gather, your second problem is caused by checking the end position and assuming that there are no obstacles in between. One solution would be to define a collision detection step-size (stepSize) which would have to be smaller than the size of your smallest obstacle. Then instead of checking just the end position, check for obstacles at playerPosition + stepSize, playerPosition + (2*stepSize)... until you reach the end position.

This is just a quick and dirty method and will likely fail when not using rectangles. Another method would be Cohen-Sutherland, which is designed for clipping on a rectangular viewport. There are many other ways, depending on how complex the layout could get. Reading up on Clipping will be useful, particularly Sutherland-Hodgman for non-rectangular obstacles.