Display list
Encyclopedia
A display list is a series of graphics commands that define an output image. The image is created (rendered
) by executing the commands.
For a display device without a frame buffer, such as the old vector graphics displays
, the commands were executed every fraction of a second to maintain and animate the output. In modern systems, the commands need only be executed when they have changed or in order to refresh the output (e.g., when restoring a minimized window).
A display list can represent both two- and three-dimensional scenes. Systems that make use of a display list to store the scene are called retained mode
systems as opposed to immediate mode systems.
Perhaps the earliest popular systems with true display list was the Atari 8-bit family
. The display list (actually called so in Atari terminology) is a series of instructions for ANTIC
, the video co-processor used in these machines. This program, stored in the computer's memory and executed by ANTIC in real time, controls the GTIA video interface controller chip to create the actual screen display.
In some older computer systems such as the Commodore 64
, a display list can be defined as a CPU-driven series of writes to certain display-mode, color-control, or other visual effect registers in the video device, rather than a series of rendering commands. Thus, one must create the displayed image using some other rendering process either before or while the display list is operating. In many cases, the image is also modified or re-rendered between frames
, often with the display list turned off during this time. The image is then displayed in various ways depending on the exact way in which the display list is implemented.
Examples of display lists on these older machines might include effects such as the Amiga's HAM
modes, Commodore 64/128's FLI mode, or Rainbow Processing on the ZX Spectrum.
Many hardcopy devices also make use of display lists to avoid the necessity of a frame buffer. As an example, a high-resolution PostScript
printer printing A4 pages at 600 dpi
would need in excess of a gigabyte of RAM
for its framebuffer
. By converting the PostScript or other page description language
input into a series of graphics commands, the contents of a page can usually be represented in a more modest amount of memory. The commands can then be scan converted (or rasterized
) into pixels and fed to the printer engine a few scan lines at a time.
Rendering (computer graphics)
Rendering is the process of generating an image from a model , by means of computer programs. A scene file contains objects in a strictly defined language or data structure; it would contain geometry, viewpoint, texture, lighting, and shading information as a description of the virtual scene...
) by executing the commands.
For a display device without a frame buffer, such as the old vector graphics displays
Vector graphics
Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...
, the commands were executed every fraction of a second to maintain and animate the output. In modern systems, the commands need only be executed when they have changed or in order to refresh the output (e.g., when restoring a minimized window).
A display list can represent both two- and three-dimensional scenes. Systems that make use of a display list to store the scene are called retained mode
Retained mode
In computing, retained mode rendering is a style for application programming interfaces of graphics libraries, in which the libraries retain a complete model of the objects to be rendered.-Overview:...
systems as opposed to immediate mode systems.
Perhaps the earliest popular systems with true display list was the Atari 8-bit family
Atari 8-bit family
The Atari 8-bit family is a series of 8-bit home computers manufactured from 1979 to 1992. All are based on the MOS Technology 6502 CPU and were the first home computers designed with custom coprocessor chips...
. The display list (actually called so in Atari terminology) is a series of instructions for ANTIC
ANTIC
Alphanumeric Television Interface Controller is an early video system chip used in the Atari 8-bit family of microcomputers as well as the Atari 5200 in the 1980s. The chip was patented by Atari, Inc. in 1981...
, the video co-processor used in these machines. This program, stored in the computer's memory and executed by ANTIC in real time, controls the GTIA video interface controller chip to create the actual screen display.
In some older computer systems such as the Commodore 64
Commodore 64
The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...
, a display list can be defined as a CPU-driven series of writes to certain display-mode, color-control, or other visual effect registers in the video device, rather than a series of rendering commands. Thus, one must create the displayed image using some other rendering process either before or while the display list is operating. In many cases, the image is also modified or re-rendered between frames
Film frame
In filmmaking, video production, animation, and related fields, a film frame or video frame is one of the many still images which compose the complete moving picture...
, often with the display list turned off during this time. The image is then displayed in various ways depending on the exact way in which the display list is implemented.
Examples of display lists on these older machines might include effects such as the Amiga's HAM
Hold-and-Modify
Hold-And-Modify, usually abbreviated as HAM, is a display mode of the Commodore Amiga computer. It uses a highly unusual technique to express the color of pixels, allowing many more colors to appear on screen than would otherwise be possible....
modes, Commodore 64/128's FLI mode, or Rainbow Processing on the ZX Spectrum.
Many hardcopy devices also make use of display lists to avoid the necessity of a frame buffer. As an example, a high-resolution PostScript
PostScript
PostScript is a dynamically typed concatenative programming language created by John Warnock and Charles Geschke in 1982. It is best known for its use as a page description language in the electronic and desktop publishing areas. Adobe PostScript 3 is also the worldwide printing and imaging...
printer printing A4 pages at 600 dpi
Dots per inch
Dots per inch is a measure of spatial printing or video dot density, in particular the number of individual dots that can be placed in a line within the span of 1 inch . The DPI value tends to correlate with image resolution, but is related only indirectly.- DPI measurement in monitor...
would need in excess of a gigabyte of RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
for its framebuffer
Framebuffer
A framebuffer is a video output device that drives a video display from a memory buffer containing a complete frame of data.The information in the memory buffer typically consists of color values for every pixel on the screen...
. By converting the PostScript or other page description language
Page description language
A page description language is a language that describes the appearance of a printed page in a higher level than an actual output bitmap. An overlapping term is printer control language, but it should not be confused as referring solely to Hewlett-Packard's PCL...
input into a series of graphics commands, the contents of a page can usually be represented in a more modest amount of memory. The commands can then be scan converted (or rasterized
Rasterisation
Rasterisation is the task of taking an image described in a vector graphics format and converting it into a raster image for output on a video display or printer, or for storage in a bitmap file format....
) into pixels and fed to the printer engine a few scan lines at a time.