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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