Texture Mapping

Texture mapping wraps a flat picture onto a polygon, so a wall or a car body carries detail that would otherwise need thousands more polygons to draw. The magazines held here first use the term for Chris Roberts’ Strike Commander in 1991; within three years it defined Doom on the PC and Ridge Racer in the arcade, and by 1996 the argument had moved on to whether the mapping was done in perspective.

Fast facts

First named here: Strike Commander, Summer CES 1991 — “texture mapping, shading and use of disguised polygons” (Computer Gaming World, September 1991).
The PC generation: Ultima Underworld and Wolfenstein 3-D (1992), Doom (1993).
The arcade benchmark: Namco’s Ridge Racer (1993), “the best ever Gouraud-shaded and texture-mapped realtime polygons” (Edge, April 1994).
The PlayStation’s flaw: textures interpolated “linearly, without perspective correction” (Edge, February 1996).
Built into the N64: mip-mapping — several sizes of each texture, chosen by the hardware.

What it does

A polygon on its own is a flat patch of one colour, or a smooth shade between its corners. Texture mapping assigns each corner a position in a small image — the texture — and, as the polygon is drawn, looks up the colour for each screen pixel from the corresponding point in that image. A brick wall becomes one polygon and one picture instead of a lattice of tiny bricks.

The hard part is deciding which point in the texture each pixel should read. Stepping evenly across the texture as the renderer steps across the screen is cheap, but wrong for a surface seen at an angle: the far end of a wall covers fewer pixels than the near end, so an even step makes the texture bend and slide as the view moves. Dividing by depth for each pixel — perspective correction — fixes it at a cost the mid-1990s consoles and CPUs mostly could not pay for every pixel. Games of the period split the difference: correct every few pixels, subdivide large polygons, or keep polygons small enough that the error does not show.

On the PC

Computer Gaming World’s Summer CES report in September 1991 is the earliest use of the phrase in the magazines held here. Chris Roberts “unveiled his Strike Commander, a post-disaster air combat game using a simplified F-16 flight model. Roberts has taken his graphics techniques of texture mapping, shading and use of disguised polygons and created a near-future environment”; the requirements were “steep (one really needs 2 MB of RAM and a fast 386 to get the most out of the game)”. By February 1994 the same magazine could look back on the escalation: “Successive releases like Strike Commander and Aces Over Europe have expanded the detail on the texture maps that cover the blocky polygon shapes and, once again, the technological ante has been upped. Now, gamers need 486s”.

The first-person games followed. The September 1992 review of Wolfenstein 3-D placed it “Much like Origin’s Ultima Underworld… in a free-scrolling, texture mapped environment. Though less detailed than Underworld, the scrolling action is much faster.” The March 1994 review of Doom found “The detailed textures of the walls, ceilings, and floors, the superb shading effects, and the fluid animation provide the most believable environment”, and called the game “a huge technical improvement over id’s earlier titles”. The same issue’s report from the January CES summed up the year: “Want to talk about texture-mapping? It’s here in a lot of places.”

In the arcade

Edge used the technique to separate Namco’s Ridge Racer from Sega’s Virtua Racing in April 1994: “While Virtua Racing oozes class and, of course, has those incredible camera angles, the sheer quality of Ridge Racer’s texture-mapped images has the contest sewn up: 400 million floating-point operations per second, if anyone is interested in the maths involved, and enough polygons generated at 60fps to give a Silicon Graphics rep a heart attack.” A caption made the point plainer: “Remember the blocky pit crew in Virtua Racing? Texture-mapping makes all the difference”. Sega’s answer was the Model 2 board, whose texture-mapping chips came from Martin Marietta; by 1995 the merged Lockheed Martin was selling the same lineage to PC makers as Real3D, with a specification that listed “True-perspective corrected texture” and up to 192 mip-mapped 128×128 textures.

The PlayStation and warping textures

The PlayStation brought Ridge Racer home and made texture mapping standard on consoles, but its graphics processor stepped across textures evenly. Edge’s February 1996 feature on Sony’s in-house studio stated the problem directly: “The PlayStation can present specific problems to programmers, especially with its propensity to warp textures. Texture warping is caused by the GPU interpolating texture coordinates linearly, without perspective correction.” Tenka’s designer Paul Hilton did not expect a cure “without severely limiting the graphical-environment”, and the feature added that “the PlayStation’s habit of smearing larger polygons when they reach the edges of the screen” was likewise “something that cannot be avoided”.

The magazine had already taken a position in October 1995, answering a reader: “Given that the PlayStation is a fraction of the cost of a high-end Pentium PC and yet is considerably more powerful, its lack of perspective correction is a small and excusable omission.” Reviews treated the warping as a known quantity. Alien Trilogy’s engine, in April 1996, “very rarely surrenders to PlayStation’s habit of warping textures when it fancies.”

The Nintendo 64 and mip-mapping

N64 Magazine’s first issue, in April 1997, gave its readers a glossary: “Texture mapping: Mapping a 2D pattern of pixels onto a 3D polygon. Texture detailing: Having more than one texture for a particular object. The machine picks the right one, so detail is preserved as you zoom in. Tri-linear mip map interpolation: (Good grief.)” Its October 1997 graphics feature explained why that mattered: “The more you ‘zoom in’ on a texture, the more blocky it becomes.” The Nintendo 64 “allows designers to store a number of different versions of each texture, and it decides for itself which version to be used based on the distance from the camera or the angle of view. The designers at DMA working on Silicon Valley, for instance, use a set of six versions of each texture at definitions of 32x32 pixels, 16X16, 8x8… and so on to 1x1.” The magazine was careful about the claim: “people have been doing all that in PC games for ages. What’s wonderful is that the N64 can handle all that for itself — it’s built into the hardware.”

The cost, and the cards that paid it

PC Zone in May 1996 named texture mapping as “one of the biggest killers of frame rates… The effort needed to wrap those pretty bitmaps round polygons can cause serious strain to even the fastest CPU”, and observed that flight simulators such as US Navy Fighters and Apache Longbow “really benefit from leaving textures out”. Perspective correction became a selling point for the first PC 3D accelerators. PC Gamer’s PowerVR feature list in March 1996 included “Perspective-correct textures do not bend or warp”; Edge’s June 1996 round-up marked Yamaha’s earlier chip down for “no perspective-correct textures” and noted Rendition’s Vérité “offers perspective-correct texturing, bilinear filtering, z-buffering, alpha effects”, with id already calling it “the premier platform for Quake”.

Images on polygons