Sprite (computer graphics)


In computer graphics, a sprite is a two-dimensional bitmap that is integrated into a larger scene, most often in a 2D video game. The term was first used by Danny Hillis at Texas Instruments in the late 1970s.
Originally sprites referred to fixed-sized objects composited together, by hardware, with a background. This composition occurs as each scan line is prepared for the video output device, such as a CRT, without involvement of the main CPU and without the need for a full-screen frame buffer. Sprites can be positioned or altered by setting attributes used during the hardware composition process.
Systems with hardware sprites include the TI-99/4A, Atari 8-bit family, Commodore 64, Nintendo Famicom / NES, Amiga, Sega Mega-Drive / Genesis, and many coin-operated arcade machines of the 1980s. Sprite hardware varies in how many sprites are supported, how many can be displayed on a single scan line, the dimensions and colors of each sprite, and special effects such as scaling or reporting pixel-precise overlap.
Use of the term sprite has expanded to refer to any two-dimensional bitmap used as part of a graphics display, even if drawn into a frame buffer instead of being composited on-the-fly at display time.

History

The use of sprites originated with arcade games. The first video game to represent player characters as human player images was Taito's Basketball, which was licensed in February 1974 to Midway, releasing it as TV Basketball in North America.
Signetics devised the first chips capable of generating sprite graphics for home systems. The Signetics 2636 video processors were first used in the 1978 1292 Advanced Programmable Video System and later in the 1979 Elektor TV Games Computer.
The Atari VCS, released in 1977, features a hardware sprite implementation where five graphical objects can be moved independently of the game playfield. The term sprite was not in use at the time. The VCS's sprites are called movable objects in the programming manual, further identified as two players, two missiles, and one ball. These each consist of a single row of pixels that are displayed on a scan line. To produce a two-dimensional shape, the sprite's single-row bitmap is altered by software from one scan line to the next.
The 1979 Atari 400 and 800 home computers feature similar, but more elaborate, circuitry capable of moving eight single-color objects per scan line: four 8-bit wide players and four 2-bit wide missiles. Each is the full height of the display—a long, thin strip. DMA from a table in memory automatically sets the graphics pattern registers for each scan line. Hardware registers control the horizontal position of each player and missile. Vertical motion is achieved by moving the bitmap data within a player or missile's strip. The feature was called player/missile graphics by Atari.
The Namco Galaxian arcade system board, for the 1979 arcade game Galaxian, featured animated, multi-colored sprites. It pioneered a sprite system that animated pre-loaded sprites over a scrolling background, which became the basis for Nintendo's Radar Scope and Donkey Kong arcade hardware and home consoles such as the Nintendo Entertainment System. According to Steve Golson from General Computer Corporation, the term "stamp" was used instead of "sprite" at the time.
The term sprite was first used in the graphic sense by one of the definers of the Texas Instruments 9918 video display processor. The term was derived from the fact that sprites, rather than being part of the bitmap data in the framebuffer, instead "floated" around on top without affecting the data in the framebuffer below, much like a ghost or "sprite". By this time, sprites had advanced to the point where complete two-dimensional shapes could be moved around the screen horizontally and vertically with minimal software overhead.

Systems with hardware sprites

These are base hardware specs and do not include additional programming techniques, such as using raster interrupts to repurpose sprites mid-frame.
Computer systemSprite hardwareYearSprites on screenSprites on lineMax. texels on lineTexture widthTexture heightColorsHardware zoomRotationBackgroundCollision detectionTransparencySource
Amstrad Plus19901616?1616151 bitmap layerColor key
Atari 2600TIA197753171, 826211 bitmap layerColor key
Atari 8-bit familyGTIA/ANTIC197988402, 8128, 2561,31 tile or bitmap layerColor key
Commodore 64VIC-II19828896, 19212, 24211, 31 tile or bitmap layerColor key
Amiga Denise1985Arbitrary812816Arbitrary3, 15 list2 bitmap layersColor key
Amiga Lisa1992Arbitrary851216, 32, 64Arbitrary3, 152 bitmap layersColor key
ColecovisionTexas Instruments TMS99181983324648, 168, 1611 tile layerColor key
Texas Instruments TI-99/4ATexas Instruments TMS99181981324648, 168, 1611 tile layerColor key
Gameduino2011256961,53616162551 tile layerColor key
IntellivisionSTIC AY-3-89001979886488,1611 tile layerColor key
MSXTexas Instruments TMS99181983324648, 168, 1611 tile layerColor key
MSX2Yamaha V993819863281288, 168,161, 3, 7, 15 per line1 tile or bitmap layerColor key
MSX2+ / MSX turbo RYamaha V995819883281288,168,161, 3, 7, 15 per line1 tile or bitmap layerColor key
Namco Pac-Man
TTL19806696161631 tile layerColor key
TurboGrafx-16HuC6270A1987641625616, 3216, 32, 64151 tile layerColor key
Namco Galaxian
TTL197977112161631 tile layerColor key
Nintendo Donkey Kong, Radar Scope
197912816256161631 tile layerColor key
Nintendo DSIntegrated PPU20041281281,2108, 16, 32, 648, 16, 32, 6465,536, affine, affine4 layers per screen; each layer is independentColor key, blending
NES/FamicomRicoh RP2C0x PPU19836486488, 1631 tile layerColor key
Game BoyIntegrated PPU198940108088, 1631 tile layerColor key
Game Boy AdvanceIntegrated PPU200112812812108, 16, 32, 648, 16, 32, 6415, 255, affine, affine4 layers, 2 layers, and 1 affine layer, 2 affine layersColor key, blending
Master System,
Game Gear		VDP
19856481288, 168, 16151 tile layerColor key
Sega GenesisYM7101 VDP
198880203208, 16, 24, 328, 16, 24, 32152 tile layersColor key
Sega OutRun 198612812816008 to 5128 to 25615, anisotropic2 tile layers and 1 bitmap layerAlpha
Sharp X68000Cynthia jr., Cynthia 1987128325121616151-2 tile layers and 1-4 bitmap layersColor key
Neo GeoLSPC2-A219903849615361616 to 512151 tile layerColor key
Super NES/
Super Famicom		S-PPU1, S-PPU21990128342728, 16, 32, 648, 16, 32, 64153 tile layers or 1 affine mapped tile layerColor key, averaging
Computer systemSprite hardwareYearSprites on screenSprites on lineMax. texels on lineTexture widthTexture heightColorsHardware zoomRotationBackgroundCollision detectionTransparencySource

Use in 3D rendering

2D images with alpha channels constrained to face the camera may be used in 3D graphics. They are common for rendering vegetation, to approximate distant objects, or for particle effects. These are sometimes called "billboards" or "Z-sprites". If rendered on the fly to cache an approximate view of an underlying 3D model, such sprites are called impostors. Modern GPU hardware can mimic sprites with two texture-mapped triangles or specific primitives such as point sprites.

Synonyms

Some hardware makers used terms other than sprite.
Player/Missile Graphics was a term used by Atari, Inc. for hardware-generated sprites in the Atari 8-bit computers and Atari 5200 console. The term reflected the usage for both characters and smaller associated objects that share the same color. The earlier Atari 2600 and some Atari arcade games also used player, missile, and ball for sprites.
Movable Object Block, or MOB, was used in MOS Technology's graphics chip literature However, Commodore, the main user of MOS chips and the owner of MOS for most of the chip maker's lifetime, used the term sprite for the Commodore 64.
The developer manuals for the Nintendo Entertainment System, Super NES, and Game Boy refer to sprites as OBJs, and the region of RAM used to store sprite attributes and coordinates was known as OAM. This also applies on the Game Boy Advance and Nintendo DS handheld systems.