You might be able to make a separate array called immediateEnvironment or
something like that which will periodically be updated, maintaining a list
of only near by objects to be considered.
 

-----Original Message-----
From: gamers-boun...@audyssey.org [mailto:gamers-boun...@audyssey.org] On
Behalf Of Rynhardt Kruger
Sent: Tuesday, December 07, 2010 5:31 AM
To: Gamers Discussion list
Subject: Re: [Audyssey] game objects in memory

Hi Cara,

The reason I thought the 3d array would be faster is:
Lets say you want to check if the player object moves into a wall when it
takes a step. In the case where every object has attributes for the 3d
coordinate, you have to search through all the objects currently in the
level and check if one of them is at the position of the players next
position. If all the objects are stored in a 3d array, it requires only
using the players next location as an array index and checking if an object
occupies that array element. In languages like c or c++, getting an array
element requires only the calculation of the correct offset in memory based
on the array index and element size and referencing that location in memory.

In this case I'd thought of storing wall-like elements in the array apposed
to rooms.
Another way might be to (as you said) give each object bounding coordinates
e.g. a left upper coordinate and a right lower coordinate and have all the
objects in an array or other data structure. May be having rooms in stead of
walls represented by objects will decrease the number of objects so the
search time isn't so big?
A reason I like this method is that rooms can have interesting shapes e.g. a
round room and that you can move a hole room to another location, possibly
moving everything inside as well to create a vehicle like object.

Take care,

Rynhardt

* Cara Quinn <caraqu...@draconisentertainment.com> [101207 07:53]:
> Rynhardt;
> 
> -It occurred to me that I didn't completely answer your question in my 
> last note, so my apologies. :)
> 
> In my own personal opinion, yes, it's good to have map data in an array,
as well as using a flexible coordinate system as in my code example.
HOwever, even though game objects can still rely on a coordinate system to
move within the game, they can still be stored in an array as well.
> 
> I.E. one could use two arrays in-game; one to store the amount of active
entities and the other to represent rooms in a level. Within the rooms
array, game entities can freely move in 3D space using the usual 3D
coordinate system we're discussing.
> 
> this is one approach I personally like, but it's also not perfect in my
opinion.
> 
> For one thing, using one element of an array per room, can make it
difficult to accurately or easily map certain complex room layouts, though
on the up-side, it can be really easy to juggle and switch rooms around to
cause some really neat effects for cool game-play.
> 
> Perhaps my very fav mapping type would simply be to map out the entire
space with a coordinate system and simply take the 3D coordinate-based
physics approach and rely on collision management and such?
> 
> -Just my thoughts?
> 
> -Hope this comes closer to answering your questions / addressing your
comments?
> 
> Smiles,
> 
> Cara :)
> On Dec 6, 2010, at 5:22 PM, Cara Quinn wrote:
> 
> Hi Rynhardt;
> 
> ACtually collision detection really isn't that expensive. Here's some C++
for checking two axis-aligned bounding boxes in 3D.
> 
> // set the lower and upper coordinates of each box // and set their 
> position
> 
> Box A (-1.0, -1.0, -1.0, 1.0, 1.0, 1.0); A.setPosition (3.0, 3.0, 
> 3.0);
> 
> Box B (-1.0, -1.0, -1.0, 1.0, 1.0, 1.0); B.setPosition (0.0, 0.0, 
> 0.0);
> 
> // check to see if any part of the above boxes touch or overlap
> 
> if((A.lower.x <= B.upper.x && A.lower.y <= B.upper.y && A.lower.z <= 
> B.upper.z) && (A.upper.x >= B.lower.x && A.upper.y >= B.lower.y && 
> A.upper.z >= B.lower.z)) {
> 
> // Manage collision
> 
> }
> 
> In this case, the two boxes are not touching, as the bottom-most point of
A is at 2.0, 2.0, 2.0 and the top-most point of B is at 1.0, 1.0, 1.0 so
there's a length of one coordinate between them. Does this make sense??
> 
> The above code is all you need to detect whether two boxes in 3D space
touch or overlap each other. This really isn't overly intensive. YOu can
also check for collision of spheres easily too, but it is a bit more
expensive than the above, but it is equally simple, relying on the
Pythagorus theorem. Basically you can just check the length of the line
between the centers of two spheres and see if it's less than or greater than
the radii of each sphere. So if the two radii add up to (or are greater
than) the distance you just found, then the spheres are touching or
overlapping.
> 
> On the subject of arrays, (depending on the type of array) it's not
necessarily any less expensive to access an array vs doing something like
the above every frame of a game, since the system may need to move through
the array to find what it needs, regardless of how easy it looks to the
user. so just because you can call an element of an array as in array[x]
doesn't mean the system doesn't need to do any work to access that element.
> 
> There are faster ways of storing data which are easier on the system 
> in C++ but I'm not as familiar with them as I'd like, so forgive me 
> but I just know they're there, but have no explanation for you. :)
> 
> Anyway, hope this sheds some light?
> 
> Smiles,
> 
> Cara :)
> On Dec 6, 2010, at 3:19 PM, Rynhardt Kruger wrote:
> 
> Hi,
> 
> Another question to the devs on this list:
> 
> What have you find to be the best way of representing the map and other
game objects in software?
> Two ways I can think of is to either have everything in an big 3d 
> array, or to give each object attributes specifying the 3d position.
> 
> Advantages of giving each object an x y and z attribute:
> * objects can have floating point positions
> * uses less memory than the array method (not really an issue anymore)
> * More than one object can be in the same position (think of doors or 
> walking through walls in SOD)
> * Possible for objects to be bigger than one unit e.a. having a start 
> position as well as an end position
> 
> Disadvantages:
> * Detecting collisions may be expensive as all the objects need to be
searched to find an object at a specific position. 
> Something like binary search may be useful, but then all the objects must
be sorted every time an object moves.
> * Increasing the number of objects in the game may decrease 
> performance as the list of objects to be searched gets longer.
> 
> Advantages of the 3d array method:
> * Very fast to reference an object at a specific position.
> This makes path finding and collision detection very fast.
> * One object may be placed in several array locations, e.g. having a 
> lot of references/pointers in the array point to one wall object.
> * If the array size stays constant, adding more objects will not have such
a great effect on game performance.
> 
> Disadvantages:
> * Not possible to have more than one object at the same position, unless
each array location points to another list.
> * Not possible for an object to be bigger than one unit.
> * Not possible for objects to have floating point positions.
> 
> Something I've missed?
> 
> Another way might be to combine the two approaches, e.g. having all 
> fixed objects like walls and floors be placed in a 3d array, and the
movable objects like the player and items use the other method.
> 
> What are your thoughts on this?
> 
> Take care,
> 
> Rynhardt
> 
> 
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