2D游戏平铺碰撞检测

我有这样的东西:

        // checking on which tile are players corners
        // ignore this big mess below, please. It can be put in smaller
        //  equations, but for now it does its job
        left_downX = ((int)Position.X) / 32 * 32 / 32 - map.mapOffsetX / 32 * 32 / 32;
        left_downY = ((int)Position.Y + height) / 32 * 32 / 32 - map.mapOffsetY / 32 * 32 / 32;
        right_downX = ((int)Position.X + width) / 32 * 32 / 32 - map.mapOffsetX / 32 * 32 / 32;
        right_downY = ((int)Position.Y + height) / 32 * 32 / 32 - map.mapOffsetY / 32 * 32 / 32;
        left_upX = ((int)Position.X) / 32 * 32 / 32 - map.mapOffsetX / 32 * 32 / 32;
        left_upY = ((int)Position.Y) / 32 * 32 / 32 - map.mapOffsetY / 32 * 32 / 32;
        right_upX = ((int)Position.X + width) / 32 * 32 / 32 - map.mapOffsetX / 32 * 32 / 32;
        right_upY = ((int)Position.Y) / 32 * 32 / 32 - map.mapOffsetY / 32 * 32 / 32;
        // checking if there is collision and responding to it
        if (map.mapData[left_downX, left_downY] == (int)Map.Tiles.air &&
            map.mapData[left_upX, left_upY] == (int)Map.Tiles.air)
        {
            if (keyboardState.IsKeyDown(Keys.A))
            {
                Speed.X = playerSpeed;
                Direction.X = MOVE_LEFT;
            }
        }
        if (map.mapData[right_downX, right_downY] == (int)Map.Tiles.air &&
            map.mapData[right_upX, right_upY] == (int)Map.Tiles.air)
        {
            if (keyboardState.IsKeyDown(Keys.D))
            {
                Speed.X = playerSpeed;
                Direction.X = MOVE_RIGHT;
            }
        }
        if (map.mapData[left_downX, left_downY] == (int)Map.Tiles.air &&
            map.mapData[right_downX, right_downY] == (int)Map.Tiles.air)
        {
            if (keyboardState.IsKeyDown(Keys.S))
            {
                Speed.Y = playerSpeed;
                Direction.Y = MOVE_DOWN;
            }
        }
        if (map.mapData[left_downX, left_downY] == (int)Map.Tiles.air &&
            map.mapData[right_downX, right_downY] == (int)Map.Tiles.air)
        {
            if (keyboardState.IsKeyDown(Keys.W))
            {
                Speed.Y = playerSpeed;
                Direction.Y = MOVE_UP;
            }
        }

当它看起来正常工作时，它没有。例如，当玩家与地面碰撞时，它会停留在地面上，不能移动到任何方向。这与只与侧面的瓷砖碰撞时类似，但在那里，你可以移动到不同的一侧。

我做错了什么?也许有更好的方法来检查碰撞而不用遍历所有贴图?