I''ve been playing RollerCoaster Tycoon lately, and i''ve started to have some "how''d they do that?" questions. I''m not sure if any of yall''d know, but i''m still curious! 1. How the nutty are all those people handled? How can 1000 people all think and find their way around in real-time?! 2. How does it draw all that stuff that fast?! I mean, it has to draw the terrain, the trees and junk, the paths, the rides, and ALL those people! How does it do that with any speed at all? 3. How did he make the user able to change the color of everything?! 4. How does he change the lighting between rainy and sunny days?

1) Fast computers & efficent code
2) He doesn''t, DirectDraw does; It uses a tile engine if you want to track down more info
3) Simple pixel replacement code
4) Probably the same as 3, maybe some alpha blending

Magmai Kai Holmlor
- The disgruntled & disillusioned

I thought I might share what little I know about the game.

Firstly, it is almsot 100% written in assembly language. Read that again -- the only other code (in C) is for the DirectX / Win32 interfacing -- the rest of the code is 100% x86 asm. Most of the source is based upon Transport Tycoon, so many things (terrain handling etc) came with the old source.

The AI stuff is pretty miserable -- they get lost on paths! Each person is stored as an array, and this is just part of a larger array (lists don''t _really_ exist in assembly...). He then passes this data through some simple AI stuff, and that''s really about it from that side.

The graphics are all pre-rendered, and he uses DirectDraw to stick them to the screen. And, thanks to his assembly, he can make things really fast and efficient too. I don''t know for sure, but I think the answer to Q4 sounds pretty good to moe, or at least that''s how I''d do it. I''m not sure about Q3 thought... I know it can be done with pixel replacement, but something tells me he didn''t use that. If you want to find out for yourself, check out his website (http://www.chrissawyer.com/), and I think there''s a "Making of..." at http://www.rollercoastertycoon.com

Hope this helps!

Simon Wilson,
XEOS Digital Development