Sprite (computer graphics)

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In computer graphics, a sprite is a two-dimensional bitmap that is integrated into a larger scene.

Originally sprites referred to independent objects that are composited together, by hardware, with other elements such as a background.[1] This 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.[1] Sprites can be positioned or altered by setting attributes used during the hardware composition process. Examples of systems with hardware sprites include the Atari 8-bit family, Commodore 64, Nintendo Entertainment System, Sega Genesis, and many coin-operated arcade machines of the 1980s.

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.

The act of creating sprites is a form of pixel art. It is sometimes referred to as spriting, especially in the hobbyist community.

When multiple smaller images are combined into a single bitmap to save memory, the resulting image is called a sprite sheet or texture atlas.

History[edit]

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.[2][3]

Signetics devised the first video/graphics processors capable of generating sprite graphics for home systems. The Signetics 2636 video processors were first used in the 1976 Radofin 1292 Advanced Programmable Video System.

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.[4] 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 scanline to the next.

The Atari 400 and 800 home computers of 1979 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.[5] 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.[6] According to Steve Golson from General Computer Corporation, the term "stamp" was used instead of "sprite" at the time.[7]

The Elektor TV Games Computer was an early microcomputer capable of generating sprite graphics, which Signetics referred to as "objects".

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).[8] 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.

The CPU would instruct the external chips to fetch source images and integrate them into the main screen using direct memory access channels. Calling up external hardware, instead of using the processor alone, greatly improved graphics performance. Because the processor was not occupied by the simple task of transferring data from one place to another, software could run faster; and because the hardware provided certain innate abilities, programs were also smaller.

Systems with hardware sprites[edit]

These are base hardware specs and don't 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 [9]
Atari 2600 TIA 1977 5 3 17 1, 8 262 1 1, 2, 4, 8× horizontal Horizontal mirroring 1 bitmap layer Yes Color key [10]
Atari 8-bit family GTIA/ANTIC 1979 8 8 40 2, 8 128, 256 1,3 1, 2× vertical, 1, 2, 4× horizontal No 1 tile or bitmap layer Yes Color key [11]
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 [12]
Commodore Amiga
(OCS)
Denise 1985 Arbitrary 8 128 16 Arbitrary 3, 15 Vertical by display list No 2 bitmap layers Yes Color key [13]
Commodore Amiga
(AGA)
Lisa 1992 Arbitrary 8 512 16, 32, 64 Arbitrary 3, 15 Vertical by display list No 2 bitmap layers Yes Color key
Gameduino 2011 256 96 1,536 16 16 255 No Yes 1 tile layer Yes Color key [14]
Namco Pac-Man
(arcade)
1980 8 8 128 16 16 3 No Horizontal and vertical mirroring 1 tile layer Yes Color key [15]
NEC TurboGrafx-16/
PC Engine
HuC6270A 1987 64 16 256 16, 32 16, 32, 64 15 No No 1 tile layer Yes Color key
Nintendo Donkey Kong, Radar Scope
(arcade)
1979 128 16 256 16 16 3 Integer Horizontal and vertical mirroring 1 tile layer Yes Color key [16]
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 [17]
Nintendo Entertainment System/Famicom Ricoh RP2C0x PPU 1983 64 8 64 8 8, 16 3 No Horizontal and vertical mirroring 1 tile layer Partial Color key [18]
Nintendo Game Boy Integrated PPU 1989 40 10 80 8 8, 16 3 No Horizontal and vertical mirroring 1 tile layer No Color key [19]
Nintendo 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 [20]
Sega 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 [21][22]
Sega Mega Drive/
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 [23][24]
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 [25][26][27][28][29][30][31]
Sega Saturn,
ST-V
VDP1
(Model 1/Model 2 arcade derived, framebuffer-based)
1994 16,384 555 4443 8 to 504 1 to 255 15 to 32,768 Yes Yes, rotation and distortion 3-6 tile layers and 1-4 bitmap layers Yes Alpha [32][33]
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 [34][35][36]
SNK 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 [37][38][39]
Sony PlayStation,
Namco System 11
GPU (framebuffer-based) 1994 4000 128 1024 8, 16, 256 8, 16, 256 15, 255 Yes Yes 1 bitmap layer Partial Alpha [40][41]
Super NES/
Super Famicom
S-PPU1, S-PPU2 1990 128 34 272 8, 16, 32, 64 8, 16, 32, 64 15 Background only Background only 3 tile layers or 1 affine mapped tile layer Yes Color key, averaging
- Texas Instruments TMS9918 1979 32 4 64 8, 16 8, 16 1 1, 2× integer No 1 tile layer Partial Color key [42]
- 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
- 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
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[edit]

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." The technique was most heavily used in Sega game machines in the late 1990s, prior to the era of polygon rendering. If rendered on the fly to cache an approximate view of an underlying 3D model, such sprites are called impostors.[43] Modern hardware may have a specific mode for rendering such point sprites without needing each corner to be defined, or these may be generated by vertex shaders.

Synonyms[edit]

Some hardware makers used terms other than sprite, and other terms exist to describe various forms of software-rendering of sprites:

  • Player-Missile Graphics was a term used by Atari, Inc. for hardware-generated sprites in the company's early coin-op games, the Atari 2600 and 5200 consoles and the Atari 8-bit computers. The term reflected the usage for both characters ("players") and other objects ("missiles"). They had restricted horizontal size (8 or 2 pixels, albeit with scalability) and vertical size equal to height of the entire screen.
  • 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, applied the common term "sprite", except for Amiga line of home computers, where MOB was the preferred term.
  • The developer manuals for the Nintendo Entertainment System, Super NES, and Game Boy referred 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 still applies today on the Game Boy Advance and Nintendo DS handheld systems. However, Nintendo Power referred to them as sprites in articles about the NES architecture in the magazine's third year.
  • Software sprites were used to refer to subroutines that used bit blitting to accomplish the same goal on systems such as the Atari ST and the Apple II whose graphics hardware had no sprite capability.

See also[edit]

References[edit]

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  2. ^ Video Game Firsts, The Golden Age Arcade Historian (November 22, 2013)
  3. ^ Basketball Flyer (1974), Arcade Flyer Museum
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  6. ^ Making the Famicom a Reality, Nikkei Electronics (September 12, 1994)
  7. ^ Steve Golson (2016). Classic Game Postmortem: 'Ms. Pac-Man' (Conference). Game Developers Conference. Event occurs at 20:30. Retrieved 2017-01-26. […] 6 moving characters, what you would call today "sprites" we called them "stamps" back then, […]. 
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  14. ^ "Gameduino Specifications". excamera.com. 
  15. ^ Montfort, Nick; Bogost, Ian (9 January 2009). "Racing the Beam: The Atari Video Computer System". MIT Press – via Google Books. 
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  42. ^ TEXAS INSTRUMENTS 9900: TMS9918A/TMS9928AITMS9929A Video Display Processors (PDF). Retrieved 2011-07-05. 
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