Sprite (computer graphics)

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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. [1]

Contents

Originally sprites referred to fixed-sized objects composited together, by hardware, with a background. [2] 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. [2] Sprites can be positioned or altered by setting attributes used during the hardware composition process.

Systems with hardware sprites include the TI-99/4A (1979), Atari 8-bit family (1979), Commodore 64 (1982), Nintendo Famicom / NES (1983), Amiga (1985), Sega Mega-Drive / Genesis (1988), 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 (which is often a lower number), 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 (by either software or a GPU) 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. [3] [4]

Signetics devised the first chips capable of generating sprite graphics (referred to as objects by Signetics) 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. [5] 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 displaya 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. [6] 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. [7] According to Steve Golson from General Computer Corporation, the term "stamp" was used instead of "sprite" at the time. [8]

The term sprite was first used in the graphic sense by one of the definers of the Texas Instruments 9918(A) video display processor (VDP). [9] 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 line Texture widthTexture heightColorsHardware zoom Rotation Background Collision detection Transparency Source
Amstrad Plus 19901616?1616151, 2, 4× vertical, 1, 2, 4× horizontalNo1 bitmap layerNoColor key [10]
Atari 2600 TIA 197753171, 826211, 2, 4, 8× horizontalHorizontal mirroring1 bitmap layerYesColor key [11]
Atari 8-bit family GTIA/ANTIC 197988402, 8128, 2561,31, 2× vertical, 1, 2, 4× horizontalNo1 tile or bitmap layerYesColor key [12]
Commodore 64 VIC-II 19828896, 19212, 24211, 31, 2× integerNo1 tile or bitmap layerYesColor key [13]
Amiga (OCS) Denise 1985Arbitrary812816Arbitrary3, 15Vertical by display listNo2 bitmap layersYes Color key [14]
Amiga (AGA) Lisa 1992Arbitrary851216, 32, 64Arbitrary3, 15Vertical by display listNo2 bitmap layersYesColor key
Colecovision Texas Instruments TMS9918 1983324648, 168, 1611, 2× integerNo1 tile layerPartialColor key
Texas Instruments TI-99/4A Texas Instruments TMS9918 1981324648, 168, 1611, 2× integerNo1 tile layerPartialColor key
Gameduino 2011256961,5361616255NoYes1 tile layerYesColor key [15]
Intellivision STIC AY-3-89001979886488,1611, 2, 4, 8× vertical, 1, 2× horizontalHorizontal and vertical mirroring1 tile layerYesColor key [16]
MSX Texas Instruments TMS9918 1983324648, 168, 1611, 2× integerNo1 tile layerPartialColor key [17]
MSX2 Yamaha V9938 19863281288, 168,161, 3, 7, 15 per line1, 2× integerNo1 tile or bitmap layerPartialColor key
MSX2+ / MSX turbo R Yamaha V9958 19883281288,168,161, 3, 7, 15 per line1, 2× integerNo1 tile or bitmap layerPartialColor key
Namco Pac-Man
(arcade)
TTL1980669616163NoHorizontal and vertical mirroring1 tile layerNoColor key [18]
TurboGrafx-16 HuC6270A1987641625616, 3216, 32, 6415NoNo1 tile layerYesColor key
Namco Galaxian
(arcade)
TTL19797711216163NoHorizontal and vertical mirroring1 tile layerNoColor key [19] [20] [21]
Nintendo Donkey Kong, Radar Scope
(arcade)
19791281625616163IntegerNo1 tile layerYesColor key [22]
Nintendo DS Integrated PPU20041281281,2108, 16, 32, 648, 16, 32, 6465,536Yes, affine Yes, affine 4 layers per screen; each layer is independentNoColor key, blending [23]
NES/Famicom Ricoh RP2C0x PPU 19836486488, 163NoHorizontal and vertical mirroring1 tile layerPartialColor key [24]
Game Boy Integrated PPU198940108088, 163NoHorizontal and vertical mirroring1 tile layerNoColor key [25]
Game Boy Advance Integrated PPU200112812812108, 16, 32, 648, 16, 32, 6415, 255Yes, affine Yes, affine 4 layers, 2 layers, and 1 affine layer, 2 affine layersNoColor key, blending [26]
Master System,
Game Gear
VDP
(TMS9918-derived)
19856481288, 168, 16151, 2× integer, 1, 2× verticalBackground tile mirroring1 tile layerYesColor key [27] [28]
Sega Genesis YM7101 VDP
(SMS VDP-derived)
198880203208, 16, 24, 328, 16, 24, 3215NoHorizontal and vertical mirroring2 tile layersYesColor key [29] [30]
Sega OutRun (arcade)198612812816008 to 5128 to 25615Yes, anisotropic Horizontal and vertical mirroring2 tile layers and 1 bitmap layerYesAlpha [31] [32] [33] [34] [35] [36] [37]
Sharp X68000 Cynthia jr. (original), Cynthia (later models)1987128325121616151, 2× integerHorizontal and vertical mirroring1-2 tile layers and 1-4 bitmap layersPartialColor key [38] [39] [40]
Neo Geo LSPC2-A219903849615361616 to 51215Sprite shrinkingHorizontal and vertical mirroring1 tile layerPartialColor key [41] [42] [43]
Super NES/
Super Famicom
S-PPU1, S-PPU21990128342728, 16, 32, 648, 16, 32, 6415Background onlyHorizontal and vertical mirroring3 tile layers or 1 affine mapped tile layerYesColor key, averaging
Computer systemSprite hardwareYearSprites on screenSprites on lineMax. texels on line Texture widthTexture heightColorsHardware zoom Rotation Background Collision detection Transparency Source

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. [44] 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. [45] The term reflected the usage for both characters ("players") and smaller associated objects ("missiles") 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 (data sheets, etc.) 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 (short for "objects"), and the region of RAM used to store sprite attributes and coordinates was known as OAM (Object Attribute Memory). This also applies on the Game Boy Advance and Nintendo DS handheld systems.

See also

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