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Help with a simple 3D engine

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Guest Anonymous Poster
I am wanting to create a simple 3D engine kind of like the old Bard's Tale games (except using Direct3DRM
rather than raycasting).
The ground will be flat and all of the walls will be perpendicular to the ground. The movement will
be a square at a time and you will only be able to turn 90 degrees at a time. So I am dealing with 4 possible
directions. I have a couple of questions regarding this:

1) How should I store level data so that I can build my little 3D world based on it? Should I use 2D arrays like
a tile game or is something else better for 3D worlds?? Should the walls be built from cubes?

2) I need help with collision detection. I can only find very complex collision detection articles on the
net. I need something simpler. I just want to keep a player from walking through a wall or a
large item (fountain,tree, etc).

Any help that you can provide will be appreciated. Thanks.

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Well, if you want to make a _simple_ 3d engine, ala WolfenStein3d, you basically need to plot out your maze on a 2d graph. The easiest way is to just fill a square if it's a wall, and leave it empty if it's empty (for example:

struct square
int isfilled;
) grid[xsize][ysize];

You can of course add fields to hold more data like what texture you want to put on each face, etc. Finally, you need a scalar factor like:

In the 3d world, your character will have a position X,Z (we'll forget Y since this is a flat game). To figure out if you should be in a space or not, you don't have to check any 3d stuff, but instead you can check against your 2d data. So if the square at X/METERS_PER_SQUARE,Z/METERS_PER_SQUARE is a 'filled' one, there's been a collision and the player shouldn't move there. Trees and other large objects can be added to the square structure (for example a tree can be a circular radius inside the square where the player can't go.) If you're using C++ you can make a square class and add a method called bool LegalMove() to it, which would make things more tidy.

A step up from that system would have each square empty, but add:
#define NORTH 0
#define EAST 1
#define SOUTH 2
#define WEST 3

int wallexists[4]
to your square structure. This way you can have thin walls instead of fat, cubefaced walls.
Collision detection would now happen if the player would end up in a different square from the one they're in now (in other words, if they cross a potential wall), so it is almost as simple. You have the added benefit of making one-way doors this way also.

The next step up from that method would be a 2d system that uses a list or array of lines for walls. Collision checks are still 2d and not so complicated (given a player's current position A and potential ending position B, draw a line from A to B. If it intersects any wall-line, a collision has occured), and you can have walls facing in any direction, not just along the cardinal directions.

Hope this gets you started

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