Pseudo-3D Road
OutRun's famous perspective
A perspective road drawn as horizontal strips bent for corners and shifted for hills, with sprites scaled by distance. Sega's Turbo had it in 1982, Out Run perfected it in 1986, and conversion programmers wrote the road routine first.
A pseudo-3D road is a perspective road drawn without 3D geometry: a stack of horizontal strips, each narrower and closer together toward the horizon, bent sideways for corners and shifted up or down for hills, with sprites scaled by distance for cars and scenery. Sega’s Turbo had the hills and tunnels in 1982, Namco’s Pole Position had the Grand Prix framing in the same year, and Sega’s Out Run (1986) set the look every home computer then tried to copy. Programmers who did those copies treated the road as the first routine written and the one everything else hung on.
Fast facts
- First described here: Sega’s Turbo, 1982 — “the most graphically outstanding car race videogame ever created” (Electronic Games, June 1982), with hills, tunnels and night.
- The reference point: Pole Position (Namco, distributed by Atari), “this year’s champion in the tire-squealing sweepstakes” in 1983.
- The high-water mark: Out Run, September 1986, “the first game to use the Super Scaler technology” by Yu Suzuki’s own account.
- The rule of the trade: “We always do the road first” — Pete Hickinson, Teque Software, 1989.
How it is done
Below a horizon line the screen is divided into strips. Each strip stands for a slice of road at some distance ahead, and the further the slice the narrower and thinner the strip, so a straight road converges to a point. The mapping is the one perspective always uses — apparent size falls with distance — and a table of it can be computed once.
A corner is not a change in the road’s shape but in where each strip is drawn. Scanning from the horizon downward, a small sideways offset is added to every strip and accumulated; a constant offset bends the road one way, and reversing its sign partway makes an S-bend. Hills move the strips vertically instead: the road ahead rises above the flat horizon on a crest and drops below it in a dip. Speed is a matter of scrolling the road’s stripes and the roadside objects toward the viewer at a rate that increases as they get closer, which is what makes near things rush and far things crawl. Cars and scenery are sprites drawn at a scale taken from the same distance table, back to front.
None of that needs multiplication in the inner loop if the tables are prepared, which is why the technique ran on a Z80 or 6502. What it cannot cheaply do is let the player leave the road, and it draws only what is directly ahead.
The road first: Chase H.Q.
The One visited Teque Software in 1989 while Pete Hickinson and Bill Caunt were converting Taito’s Chase H.Q. for Ocean, fresh from Continental Circus. Asked where they started: “On the road. We always do the road first — that’s the central routine that the entire game is based on, so it’s vital to get that working first.”
Hickinson called a moving, winding road “really just a mathematical exercise”, with one trap: “It’s not just a case of moving the road towards the screen really quickly. If you try to do that, the road looks as though it’s going the wrong way. You don’t need to create speed — only the impression of it — which can be done using a few simple routines like ‘wirelines’, where objects appear to move more slowly the further away they are, even though the actual speed doesn’t change.”
The road code was not portable between games. “The principle is pretty much the same in both games, but we’ve had to produce the road calculator and most of the maths from scratch. Chase has a more complex road system than Circus — it changes in width, passes through tunnels and even breaks into two separate roads.” Width changes were done with “small ‘snakes’ in the side of the road that move it inwards or outwards. And when two appear together (one on each side) the road is thinned or widened.”
Arcade origins
Electronic Games reviewed Sega’s Turbo in June 1982 as a terrain show: a tree-lined highway with mountains in the distance, then a city, then night with street lights, then hills where “cars moving toward the [horizon] rise and fall from view as they climb and descend”, then tunnels. That is the whole vocabulary of the pseudo-3D road, a year before Pole Position.
Pole Position — “a first-person driving game developed by Namco in Japan and distributed to this country’s arcades by Atari” — was the 1983 champion for a different reason. Its road was flat; what it added was a real circuit, Fuji Speedway, qualifying laps against a 73-second limit, and roadside billboards. Electronic Games called it “an eye-popping spectacle, but the focus here is on your car’s position regarding the other participants”.
Sega’s answer was scaling hardware. Yu Suzuki dated the line in a 1994 interview: Hang-On (July 1985), Space Harrier (December 1985, “an impressive display of Sega’s sprite-scaling technology”), Out Run (September 1986), After Burner (1987) and Power Drift (1988, “advanced sprite scaling and an axis of rotation”). Out Run, he said, “was the first game to use the Super Scaler technology”. To a British reviewer in 1987 the difference from Pole Position was the vertical: “Out Run’s road swoops up and down … you often shoot straight over the brow of a hill and mangle yourself under a truck.” ACE singled out the “large (and frighteningly solid) pieces of roadside scenery” that “hurtle past very convincingly” and the end-over-end crash when you hit them.
On home machines
The 8-bit conversions of Out Run (US Gold, Christmas 1987) could scale nothing in hardware; ACE found the C64 version gave “a good impression of speed” with fixed, learnable traffic. On the 16-bit machines the technique became a house skill for conversion studios like Teque, and on the SNES it competed with the console’s own rotating-background mode. Kemco’s Top Gear (1992) chose the software road anyway: Ritchie Brannan, “responsible for the road and sprite routines”, said its “road moves faster and the corners and hills are more extreme to try to make the game faster and more cartoon like”, and that “‘Give me a faster processor and I’ll do it’ is a poor and over-used excuse”. His next job was “a road routine with more than twice the depth of Top Gear and a much smoother feel”.