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Vol. 2, Issue 13
February 25, 2000

Beaker's Bent:

Making the Outdoors
(part 2)

by Rich "Beaker" Wyckoff




elcome back, after a long delay, to Beaker’s Bent.  It’s been two months since my last column, where I started to describe some of the techniques I’ve built up over the years for making realistic outdoor environments.  Hopefully no aspiring designers of outdoor environments have been forced into anything drastic out of frustration while waiting for this new installment.  At any rate, they can relax now as I divulge some details about the geometry of outdoor environments.

Last time, I discussed texturing and lighting, two aspects of an outdoor level which actually supercede the geometry in importance.  With excellent textures and sparkling, sun-like lighting even very simplistic geometry can capture some of the feeling of the outdoors.

Geometry of an outdoor level is highly dependent on the engine involved.  Many outdoor-oriented engines use height-mapped terrain engines.  For the true neophytes out there or those who have never touched anything beyond an FPS, a height-mapped engine uses a grid of points of varying heights, with the geometry between those points often out of the designer’s control.  It is possible to programmatically reduce detail in height-mapped terrain as it gets further away from the player, which allows for extended viewing distances as the furthers hills are rendered with the minimum number of polygons.

It is also very easy to apply fractal algorithms to a grid of points to quickly get mountains and valleys, and to make simple editing tools that can raise or lower hills.  However, this very ease of use contributes to one of the most common problems with outdoor geometry: what I call, until I can come up with a shorter description, the “metal balls in a rubber sheet” look.  In short, the most simple fractal algorithms and editing tools, which are often all that get put into a game editor for height mapped terrain, create a generic and unnatural look to the terrain.  Keep an eye out for landscapes made of many hills and valleys of similar size distinctive, bell-curve shape (as if metal balls had been pressed up through or laid down on a rubber sheet).  You’ll begin to notice this effect in the most hastily assembled outdoor scenes, both real time and pre-rendered.

There are, indeed, some parts of the real world that look similar to “rubber sheet world,” but the far more interesting parts of the world (those which you would like to put in a game) have much more variation than this.  Achieving this kind of terrain requires much more thought and hard work than merely applying fractal noise and a smoothing routine to a grid of height points, and I’ll write more about the technique in a moment.  However, the very nature of the height-mapped terrain engine also contributes to this. 

The biggest technical drawback to height-mapped terrain is that overhangs or even completely vertical surfaces are impossible to create, since none of the height points could possibly overlap another.  A secondary and related drawback is that it is difficult to reproduce very fine detail, such as the branching run-off patterns that you see on the sides of real hills, or the rounded banks of small streams.  Better height-mapped engines have variable-resolution grids, which means that in areas which need high detail such as stream banks or the foundation of a building, the spacing between height points can be decreased.  This also allows for near-vertical slopes, but still not overhangs of course.  The overhang issue can be avoided by using objects cleverly placed on or in the terrain, but it can be difficult to mask the transition between the terrain and the overhang object itself.

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Credits: Illustration © 2000 Dan Zalkus. Beaker's Bent is © 2000 Rich Wyckoff. All other content is © 1999 loonyboi productions. Unauthorized reproduction is prohibited, so don't do it or we'll sick our lawyers on you. Muhahahahahahahah. ph3ar our m@d l3gal sk1lz y0.