Right. So I was making this simple game. The player is two tiles wide, and four tiles high. My current code is really buggy (it was better before my rewrite)

Here it is:

    float newx = position.x + velocity.x;
    float newy = position.y + velocity.y;
    
    int tx = (int) newx;
    int ty = (int) newy;
    
    Tile tile = WorldHandler.currentWorld.getTile(tx, ty);
    Tile ground = WorldHandler.currentWorld.getTile((int) position.x, (int) position.y-1);
    
    if (tile.type == 0) {
        position.x = newx;
        position.y = newy;
    }
    if (ground.type != 0) {
        grounded = true;
        //position.y = Math.round(position.y);
    }       
    
    if (grounded) {
        velocity.x = 0.0f;
        velocity.y = 0.0f;
        //position.y = Math.round(position.y);
    } else {
        velocity.x = velocity.x * (1.0f - Math.min(0.1f, 1.0f));
        velocity.y += 0.0f;
    }

it basically uses the indices for performance.

But I need a decent collision detection system that wouldn't be painful to implement, would AARBs be of use here? Also, the game loop is a tick based one, it runs at 30 ticks/s.