Terrain in Games

Traditional implementation of terrain in games (1995-2002)

Navigational Constraints

The type of terrain used in a game depends on the range of navigation needed.  Some common styles of navigation are:

1. Top-down games only let you look at a downward angle, and do not have to deal with a wide range of distances.  Hither clipping and LOD is greatly simplified or not needed.
2. Unconstrained ground games let you look up or down, and get close to the surface.  They must allow a wide range of distances and levels of detail, and deal with hither clipping.  Some have third-person display modes, but allow the full navigational freedom of a 1st-person point of view.
3. Unconstrained air games are similar, but do not have to deal with drawing near objects/scenery accurately.

Traditionally, each of these styles had different tradeoffs resulting in different algorithms.  More recently with the rise of powerful GPUs (2002-) terrain rendering systems have tended to have a more unified approach which can handle any style of navigation.

Top-down examples

• Black & White
  • in their art notes, claims to have novel approaches for ground textures:
  • .. "different terrain types meld together using various criteria and filters so you should never see the same piece of texture twice on the landscape"
  • "unique texture for every square inch of the ground, allowing it to reflect all sorts of terrain – without a hard edge in sight... glistening lakes and tiny, pixel perfect ripples lapping at the coastline"
  • wireframe screenshots indicate that the terrain is a simple brute-force regular grid

Unconstrained ground examples

• Treadmarks (1999)
  • most impressive terrain in a game as of year 2000
  • dynamic LOD and a deformable(!) terrain
  • OpenGL-based, variable error threshold and clipping distance
  • very fun
  • author Seumas McNally cited ROAMing Terrain as a good starting point
  • learned many things in a conversation with Seumas, July 1999
• Colin McRae Rally (1998-)
  • for PlayStation and PC, from UK developers CodeMasters
  • very impressive-looking screenshots
  • trees look like billboards, but roads and roadsides look great
  • good art for sky textures and countryside, but is the user allowed to leave the road?
• Trespasser (1998)
  • before release, this game was intensely hyped for its terrain:
    • "Trespasser is largely an outdoor game, the most beautiful and detailed ever attempted in 3D. You will have kilometers of forest, plain, and dark jungle to cross, beautiful vistas and hidden canyons."
  • however, the released game was very disappointing
    • They used a continuous LOD approach, and their allowed error bound is enormous - resulting in visual "pops" of as much as 50 pixels or more.  The ground grid spacing is very wide, making it appear extremely planar.
    • Looked terrible on the 8MB cards common at the time, and on 16 MB / AGP systems, there were still problem with ground texture tiling too obvious, and significant elevation pops.
  • all "levels" were hand-modeled in 3DS MAX
  • approximately 30 developers were on the team. graphics people included: Mark Langerak: development lead in charge of terrain, and Scott Peter: rendering (including lighting and water modeling/rendering)

Unconstrained air examples

• Bombs-Away B17-II
  • Flight combat simulation
  • "Countryside" has no discernible elevation variation, but very good textures
  • One of the developers, Dominic Robinson of Wayward Design, tells us:
  • "65x65 cells, paged quadtrees, wavelets..."
  • "All the textures are resolution independent, procedurally generated with both color and bump channels. They currently resolve down to a feature size of 20cms ( but can go lower ). The terrain is rendered with a full sky light model, self shadowing, plus shadows from buildings and clouds. Texture areas are trimmed and composited with sub-pixel, anti-aliased cubic beziers.
  • The terrain mesh is generated on the fly from a procedurally amplified DEM height map - the current raw DEM dataset is ~600Mb ( 100m spacing 16 bit height samples ) for a sizeable chunk of NW Europe. The mesh is frame coherent and morphs to introduce/remove detail. No 'variance' or other pre-processing is required other than structuring for disk access.
  • View point and direction can be completely arbitrary, with no draw distance limit - you can zoom from an altitude in excess of 600 million feet, at which the full dataset is visible at about the size of a postage stamp, to zero feet, continuously."
• Falcon 4 , late 1990s
  • used a patchwork of re-used aerial photos for high resolution large-area coverage
  • excellent water and water boundary textures
  • supported time-of-day with sunset and stars
  • designer's notes gave insight into the terrain engine used, but they're not online anymore
  • personnel: Scott Randolph, Senior Graphics Engineer, Falcon 4.0 Team, Spectrum HoloByte/Microprose
• Joint Strike Fighter
  • developed by Innerloop, distributed by Eidos Interactive
  • from an interview with Henning Rokling of Innerloop Studios:
  • "The terrain engine - IFS, Iterated Function Systems - is a clever way of storing extremely huge terrains in very little space. It reduces the number of polygons of the terrain in the distance, while keeping the texture and elevation detail at the same high quality. We've created an in-house tool allowing us to take real-world elevation data and texture maps, and generate the math data for displaying all of this realtime. When rendered, it uses normal polygons for the mesh.
    Each terrain map has 1.125 billion billion polygons.
    Each campaign is made up of 2.4 million square miles of real world terrain. The elevation in each campaign has been taken from satellite images, with elevation correct down to a grid of 100x100 meters. In between the elevation grid, we fill in the most plausible elevation pattern through complex algorithms to make it seem real, and according to a lot of enthusiastic beta testers, it looks very realistic."
  • does not support Direct3D or OpenGL!  uses a software renderer or Glide.
  • very high-resolution and beautiful soft lighting on the terrain, but ground is much too smooth to be realistic
  • trees are very, very small billboards - probably accurate size, but much too sparse
  • cities consist of nicely-modeled rectangular buildings, but just buildings
• Flight Unlimited II from Looking Glass Studios
  • probably the most realistic aerial terrain in any PC game title as of 2003
  • uses the SF bay area as data
  • it's likely they used the BARD data and colorized it: by hand, or by algorithm, or by using color information from lower-resolution satellite images
  • from an interview with Constantine Hantzopoulos of Looking Glass Technologies:
    • An immense amount of both research and work has gone into creating ZOAR, their terrain and object rendering engine, created by their lead programmer Jaemz Fleming. Their 4 main goals were:
      • rendering 4 meter per pixel color satellite imagery
      • getting a ton of it somehow
      • rendering out to the horizon - no clipping of terrain and objects
      • no popping of terrain.
    • ZOAR removes polygons, not textures, intelligently on the fly, only renders height when needed,
    • The effect is truly rolling terrain as you get lower and lower without loss of frame rate.
    • SAIC provided them with the ortho-corrected data as they felt that having DOQ imagery to government QA specs would be better than handling it themselves
    • Super sneaky methods were used to color correct and render it all.
    • They could render 1 meter per pixel imagery if they so choose. They didn't because they don't have the storage capacity for that. That's why they went with 4 meter data. DVD though...
  • they were working on a Flight Unlimited III (but it never got distribution)