Destructible Terrain
Worms' secret weapon
The technique of modifying bitmap landscapes in real-time, famously used in Worms to create satisfying explosions that reshape the battlefield.
Destructible terrain is a landscape that the game edits while you play: a shot takes a bite out of a hillside, a digger leaves a tunnel, and every later shot has to reckon with the new shape. The idea belongs to the artillery game — two guns on either side of a hill — and reached its best-known form in Team 17’s Worms (1995), which the Amiga press summed up as an old idea with new weapons: “underneath it all, Worms IS Scorched Tanks. The addition of tunnel-digging meets with our approval, as does the dynamite.”
Fast facts
- Ancestor: the artillery game — angle, power, wind, and a hill in the way.
- Scorched Earth: Wendell Hicken’s shareware PC version, reviewed in 1993 as “a modern version of one of the oldest computer games around” with randomly generated terrain and up to ten players.
- Scorched Tanks: Michael Welch’s Amiga public-domain artillery game, on the Amiga Power 41 coverdisk (September 1994); the game Worms was compared to.
- Lemmings (1991): bashers, miners and diggers cut through the level; the nuke takes “most of the scenery” with it.
- Worms (1995): Andy Davidson’s game, written in Blitz Basic, sent in to an Amiga Format competition and picked up by Team 17 at the 1994 Amiga Trade Show.
The artillery game
The shape is old: two tanks, a hill, and a shot that has to clear it. Computer Gaming World’s shareware column called Scorched Earth “a modern version of one of the oldest computer games around”, and described what the modern version added — “play begins with the random generation of the current level, creating the terrain”, up to ten players, a purse for buying better weapons between rounds, and shots that demand “compensation for wind velocity and intervening objects”. COMPUTE’s SharePak listing of version 1.2 sold it as a “256-color VGA artillery game” with configurable “weapons, defense mechanisms, weather, economics, terrain, and much more”. Registration was $10, sent to Hicken’s home address in Sierra Madre, California.
On the Amiga the same formula circulated as public domain. Amiga Power put Michael Welch’s Scorched Tanks on its issue 41 coverdisk in September 1994 — “top ballistic fun for anything up to four players” — and noted it belonged to a lineage: “We’ve seen many of these ‘shoot the tank at the other side of the hill’ type games over the years, but this one’s got more fiddly bits, add-ons and features than all of them put together.”
Lemmings
DMA Design’s Lemmings (Psygnosis, 1991) made terrain editing a puzzle mechanic rather than a side-effect of gunfire. Three of its eight skills exist to remove level: The One’s skill list defines the basher as one who digs “horizontally through the first appropriate surface”, the miner “diagonally down through the floor”, and the digger who burrows “vertically”, while the builder adds a bridge “only twelve tiles long”. Amiga Computing’s review put it more bluntly — the basher “is a destructive fellow. His role in life is to bash a tunnel through an obstacle” — and described the nuke: “every Lemming explodes taking most of the scenery with them!”
Worms
Amiga Computing’s 1997 profile tells the origin story. Andy Davidson, “bored witless during his A levels”, started “a game in which teams of little worms did battle with each other”, tested it on customers at the Amiga shop where he worked, and took the game — “provisionally entitled Total Wormage” — to the 1994 Amiga Trade Show, where “within five minutes of presenting his two skanky looking diskettes to the Team 17 stand, they offered to sponsor and market the project”. Amiga Format’s version is that the game came in through its own reader competition and was “passed on to Team 17”; the magazine later noted that Davidson “developed Worms on the Amiga, with the Blitz Basic Coverdisk which we gave away (AF52)”, and Blitz Basic’s own adverts led with “The Language Used To Write Worms!”
Reviewers placed the game in the artillery lineage without hesitation. Amiga Power’s April 1995 preview saw “a sophisticated evolution of Scorched Tanx from AP41’s coverdisk. Imagine, if you will, a randomly-generated landscape, like the ones in Scorched Tanx only more intricate, with trees, bridges and other obstacles. Now mentally litter it with worms, equivalent to the ‘tanx’.” CU Amiga’s preview called it “a variation on the old Tanks theme” in which “your task is to destroy an enemy that is hiding somewhere in a generated landscape”. Amiga Power’s review by Jonathan Davies opened with “it’s Scorched Tanks, the PD game”, and its list of uppers named the two things the landscape added: tunnel-digging and dynamite.
The landscape was the game’s variety. Amiga Format counted “eight different terrain types in all (A500/600 owners can’t access all of them) which make a considerable difference to the way Worms plays”, and judged that “mastering the art of using terrain to best effect is part of the battle toward mastering Worms”. Davidson told Amiga Computing that “no two Worms games will ever be the same, but with rendered games you’ll never get that much variety”. The Director’s Cut went further by letting players paint their own: “by enabling players to decide the battlefield, the lethality of the weapons and even the speech of the individual worms, Andy Davidson has designed the game so it can be tailored exactly to the requirements of the individual” — the “graffiti mode” that Amiga Computing’s profile credited with “a billion levels”.
How it works
The general approach treats the landscape as a bitmap rather than a tilemap. Terrain is drawn once; an explosion is then subtracted from it by clearing a disc of pixels centred on the blast, and a tunnel is a series of small discs cleared along the digger’s path. Collision comes from the same bitmap: a projectile or character tests the pixels ahead of it, so a freshly blown crater is passable the instant it appears, with no separate map to update. Anything the landscape rests on — a floor line, water — is a boundary the bitmap does not need to describe.