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.[1]

For the technique of combining images into a single bitmap, see texture atlas.

For the process of drawing sprites, see pixel art.

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 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.[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 system	Sprite hardware	Year	Sprites on screen	Sprites on line	Max. texels on line	Texture width	Texture height	Colors	Hardware zoom	Rotation	Background	Collision detection	Transparency	Source
Amstrad Plus		1990	16	16	?	16	16	15	1, 2, 4× vertical, 1, 2, 4× horizontal	No	1 bitmap layer	No	Color key	[10]
Atari 2600	TIA	1977	5	3	17	1, 8	262	1	1, 2, 4, 8× horizontal	Horizontal mirroring	1 bitmap layer	Yes	Color key	[11]
Atari 8-bit family	GTIA/ANTIC	1979	8	8	40	2, 8	128, 256	1	1, 2× vertical, 1, 2, 4× horizontal	No	1 tile or bitmap layer	Yes	Color key	[12]
Commodore 64	VIC-II	1982	8	8	96, 192	12, 24	21	1, 3	1, 2× integer	No	1 tile or bitmap layer	Yes	Color key	[13]
Amiga (OCS)	Denise	1985	Arbitrary	8	128	16	Arbitrary	3, 15	Vertical by display list	No	2 bitmap layers	Yes	Color key	[14]
Amiga (AGA)	Lisa	1992	Arbitrary	8	512	16, 32, 64	Arbitrary	3, 15	Vertical by display list	No	2 bitmap layers	Yes	Color key
Colecovision	Texas Instruments TMS9918A	1983	32	4	64	8, 16	8, 16	1	1, 2× integer	No	1 tile layer	Partial	Color key
Texas Instruments TI-99/4A	Texas Instruments TMS9918A	1981	32	4	64	8, 16	8, 16	1	1, 2× integer	No	1 tile layer	Partial	Color key
Gameduino		2011	256	96	1,536	16	16	255	No	Yes	1 tile layer	Yes	Color key	[15]
Intellivision	STIC AY-3-8900	1979	8	8	64	8	8,16	1	1, 2, 4, 8× vertical, 1, 2× horizontal	Horizontal and vertical mirroring	1 tile layer	Yes	Color key	[16]
MSX	Texas Instruments TMS9918A	1983	32	4	64	8, 16	8, 16	1	1, 2× integer	No	1 tile layer	Partial	Color key	[17]
MSX2	Yamaha V9938	1986	32	8	128	8, 16	8,16	1, 3, 7, 15 per line	1, 2× integer	No	1 tile or bitmap layer	Partial	Color key
MSX2+ / MSX turbo R	Yamaha V9958	1988	32	8	128	8,16	8,16	1, 3, 7, 15 per line	1, 2× integer	No	1 tile or bitmap layer	Partial	Color key
Namco Pac-Man (arcade)	TTL	1980	6	6	96	16	16	3	No	Horizontal and vertical mirroring	1 tile layer	No	Color key	[18]
TurboGrafx-16	HuC6270A	1987	64	16	256	16, 32	16, 32, 64	15	No	No	1 tile layer	Yes	Color key
Namco Galaxian (arcade)	TTL	1979	7	7	112	16	16	3	No	Horizontal and vertical mirroring	1 tile layer	No	Color key	[19][20][21]
Nintendo Donkey Kong, Radar Scope (arcade)		1979	128	16	256	16	16	3	Integer	No	1 tile layer	Yes	Color key	[22]
Nintendo DS	Integrated PPU	2004	128	128	1,210	8, 16, 32, 64	8, 16, 32, 64	65,536	Yes, affine	Yes, affine	4 layers per screen; each layer is independent	No	Color key, blending	[23]
NES/Famicom	Ricoh RP2C0x PPU	1983	64	8	64	8	8, 16	3	No	Horizontal and vertical mirroring	1 tile layer	Partial	Color key	[24]
Game Boy	Integrated PPU	1989	40	10	80	8	8, 16	3	No	Horizontal and vertical mirroring	1 tile layer	No	Color key	[25]
Game Boy Advance	Integrated PPU	2001	128	128	1210	8, 16, 32, 64	8, 16, 32, 64	15, 255	Yes, affine	Yes, affine	4 layers, 2 layers, and 1 affine layer, 2 affine layers	No	Color key, blending	[26]
Master System, Game Gear	VDP (TMS9918-derived)	1985	64	8	128	8, 16	8, 16	15	1, 2× integer, 1, 2× vertical	Background tile mirroring	1 tile layer	Yes	Color key	[27][28]
Sega Genesis	YM7101 VDP (SMS VDP-derived)	1988	80	20	320	8, 16, 24, 32	8, 16, 24, 32	15	No	Horizontal and vertical mirroring	2 tile layers	Yes	Color key	[29][30]
Sega OutRun (arcade)		1986	128	128	1600	8 to 512	8 to 256	15	Yes, anisotropic	Horizontal and vertical mirroring	2 tile layers and 1 bitmap layer	Yes	Alpha	[31][32][33][34][35][36][37]
Sharp X68000	Cynthia jr. (original), Cynthia (later models)	1987	128	32	512	16	16	15	1, 2× integer	Horizontal and vertical mirroring	1-2 tile layers and 1-4 bitmap layers	Partial	Color key	[38][39][40]
Neo Geo	LSPC2-A2	1990	384	96	1536	16	16 to 512	15	Sprite shrinking	Horizontal and vertical mirroring	1 tile layer	Partial	Color key	[41][42][43]
Super NES/ Super Famicom	S-PPU1, S-PPU2	1990	128	34	272	8, 16, 32, 64	8, 16, 32, 64	15	Background only	Horizontal and vertical mirroring	3 tile layers or 1 affine mapped tile layer	Yes	Color key, averaging
Computer system	Sprite hardware	Year	Sprites on screen	Sprites on line	Max. texels on line	Texture width	Texture height	Colors	Hardware 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

• 2.5D
• Layers (digital image editing)

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