Image rendered in MDA text mode using semigraphic blocks

Text-based semigraphics or pseudographics is a primitive method used in early text mode video hardware to emulate

raster graphics upright=1, The Smiley, smiley face in the top left corner is a raster image. When enlarged, individual pixels appear as squares. Enlarging further, each pixel can be analyzed, with their colors constructed through combination of the values for ...

without having to implement the logic for such a display mode. There are two different ways to accomplish the emulation of raster graphics. The first one is to create a low-resolution all points addressable mode using a set of special characters with all binary combinations of a certain subdivision matrix of the text mode character size; this method is referred to as block graphics, or sometimes mosaic graphics. The second one is to use special shapes instead of glyphs (letters and figures) that appear as if drawn in raster graphics mode, sometimes referred to as semi- or pseudo-graphics; an important example of this is

box-drawing characters Box-drawing characters, also known as line-drawing characters, are a form of semigraphics widely used in text user interfaces to draw various geometric frames and boxes. Box-drawing characters typically only work well with monospaced fonts. In ...

. Semigraphical characters (including some block elements) are still incorporated into the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...

of any

VGA Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the PC industry within three years. The term can now ...

compatible video card, so any PC can display these characters from the moment it is turned on, even when no operating system is yet loaded. Single and double lines are still often drawn with this method when the system uses text mode; for example when running the BIOS setup program. Many of these historical ideas have been adopted into

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...

, in, for example in the Symbols for Legacy Computing, Block Elements,

Box Drawing Box Drawing is a Unicode block containing characters for compatibility with legacy graphics standards that contained characters for making bordered charts and tables, i.e. box-drawing characters. Its block name in Unicode 1.0 was Form and Chart C ...

and

Geometric Shapes Geometric Shapes is a Unicode block of 96 symbols at code point range U+25A0–25FF. U+25A0–U+25CF The BLACK CIRCLE is displayed when typing in a password field, in order to hide characters from a screen recorder or shoulder surfing. U+2 ...

Unicode block A Unicode block is one of several contiguous ranges of numeric character codes (code points) of the Unicode character set that are defined by the Unicode Consortium for administrative and documentation purposes. Typically, proposals such as the ad ...

Block graphics

For example, an 8×12 character could be divided vertically in two halves and horizontally in three parts, and then assigning "ink" and "background" values to the elements of the matrix in a binary pattern, corresponding to the binary sequence of the position in the font table of a 2×3 mosaic matrix of so-called ''squots'' (square dots) or ''sextants''. Less often used versions use a 1×6 "matrix", in which case these six "pixels" are sometimes referred to as

sixel Sixel, short for "six pixels", is a bitmap graphics format supported by terminals and printers from DEC. It consists of a pattern six pixels high and one wide, resulting in 64 possible patterns. Each possible pattern is assigned an ASCII chara ...

s. But dividing an 8×8 character in 2×2 "pixels" called ''quadrants'' was also common (it was, for example, used in the Sinclair ZX81). Sometimes the text semigraphical characters are simply incorporated into the systems font-set, sometimes special video hardware is used to directly convert the bit-pattern from video memory into the pixels. In rare cases a character matrix wasn't dividable vertically by three, for example in an 8×8 matrix the mosaic is sometimes divided so that it uses a 3:2:3 scan line scheme. The Galaksija's graphics mode is an example, although with a 4:5:4 scheme the distortion effect was minimal. The seminal use of this technology was in the

TRS-80 The TRS-80 Micro Computer System (TRS-80, later renamed the Model I to distinguish it from successors) is a desktop microcomputer launched in 1977 and sold by Tandy Corporation through their Radio Shack stores. The name is an abbreviation of '' ...

where the only way to get discrete pixels on the screen that could be turned on and off individually, (all points addressable) was by the use of a 2×3 pixel matrix of block graphics. In the case of the TRS-80 these block graphics were not incorporated into a font ROM, as later became the norm, but were generated directly from the logic pattern of six bits from the video RAM using a dedicated circuit made from

logic gate A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, ...

s. An earlier system using the same pseudo-graphics array of a 2 by 3 matrix was the Video Terminal Interface (VTI) of the Poly-88 by polymorphic systems, an S-100 bus based system predating the TRS-80. If the system also supported color, the color resolution of the resulting pixels was normally equal to the text resolution, often leading to attribute clash as the color of a pixel could not be changed on a per pixel basis, but only to one "ink", and one "background" color for all pixels within a character position. Sometimes the number of characters in the font, dedicated to block graphics, could be halved if the system also supported an "invert" attribute, as half the characters in a full block graphics font set are the logical inverse of the other half of the font set. Other tricks that were used to decrease the number of needed characters, was to use a space for the "all bits are zero" character, and to use character 7F hex for the "all bits are on" character, as character 7F hex (decimal 127) was often defined as an "all pixels on" character (this was because when using papertape punching out all seven holes, created the 7F hex "byte" which was considered to be the "DEL" or "rub-out" character). The assignment in

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...

of the rub-out character (to the code point 127) led designers of VDUs to use "rub-out" for a character square filled with "ink", which was often used to represent the cursor.

Examples of the use of block graphics

Other examples of systems that relied on the use of block graphics are: * The

ZX80 The Sinclair ZX80 is a home computer launched on 29 January 1980 by Science of Cambridge Ltd. (later to be better known as Sinclair Research). It is notable for being one of the first computers available in the United Kingdom for less than a h ...

and ZX81 character sets, where a matrix of 2×2 pixels was used, with the space and invert attribute tricks to keep the number of characters in the ROM needed down to just 7 (of the necessary 16). The

ZX Spectrum The ZX Spectrum () is an 8-bit computing, 8-bit home computer that was developed by Sinclair Research. It was released in the United Kingdom on 23 April 1982, and became Britain's best-selling microcomputer. Referred to during development as t ...

also supported block graphics as well as "real" higher-resolution graphics. In addition, on the Spectrum the system font (stored in its ROM) could be easily and instantly changed to one stored in RAM, allowing programmers to define their own semigraphical characters to suit their needs. * Other systems that used a 2×2 matrix were the

Panasonic JR-200 The Panasonic JR-200 (Panasonic Personal Computer (PPC)) was a simple, relatively early (1983), 8-bit home computer with a chiclet keyboard somewhat similar to the VTech Laser 200. It's part of the JR Series. Made of silver grey plastic, it ha ...

and the Mattel Aquarius. * The Commodore PET also had a few characters to support 2×2 text semigraphics in its PETSCII character set. The PET was also one of the first systems to rely heavily on semigraphical characters, to get any form of graphics on screen. * The TRS-80 Color Computer, and the Dragon 32/64 are good examples of systems using 2×2 matrix color semigraphics. But their

Motorola 6847 The MC6847 is a video display generator (VDG) first introduced by Motorola and used in the TRS-80 Color Computer, Dragon 32/64, Laser 200, TRS-80 MC-10/Matra Alice, PC-6000 series, NEC PC-6000 series, Acorn Atom, and the APF Imagination Machine, ...

VDC also supported a little used 6-block semigraphics mode. * Videotex and

teletext A British Ceefax football index page from October 2009, showing the three-digit page numbers for a variety of football news stories Teletext, or broadcast teletext, is a standard for displaying text and rudimentary graphics on suitably equipp ...

systems used a 2×3 matrix and one foreground ("ink"), and one background color, normally out of a set of eight colors (including black and white). Many systems used " Videotex graphics". One of the best known examples is the Acorn BBC Micro's default graphics mode ( mode 7). Other systems which used "Videotex"-like graphics are: the

ABC 80 The ABC 80 (Advanced BASIC Computer 80) was a personal computer engineered by the Swedish corporation Dataindustrier AB (DIAB) and manufactured by Luxor in Motala, Sweden in the late 1970s and early 1980s. It was introduced on the market in August ...

, the

Grundy NewBrain The Grundy NewBrain was a microcomputer sold in the early 1980s by Grundy Business Systems Ltd of Teddington and Cambridge, England. Beginnings The NewBrain project was started in 1978 when Sinclair Radionics began design work with Mike Wak ...

, many of the Acorn Eurocard systems, and the Philips P2000T, which actually used a

Teletext A British Ceefax football index page from October 2009, showing the three-digit page numbers for a variety of football news stories Teletext, or broadcast teletext, is a standard for displaying text and rudimentary graphics on suitably equipp ...

chip designed for their TV's. * The

Matra Alice The Matra & Hachette Ordinateur Alice is a home computer sold in France beginning in 1983. It was a clone of the TRS-80 MC-10, produced through a collaboration between Matra and Hachette in France and Tandy Corporation in the United States. T ...

32, Matra Alice 90 and

Philips VG5000 The VG5000μ is a computer created by Philips in 1984. It was manufactured in Le Mans by Radiotechnique (RTS) and marketed under the Philips, Radiotechnique, Radiola and Schneider Rundfunkwerke, Schneider brands. Not compatible with any other m ...

were based on the

Thomson EF9345 The EF9345 from SGS-Thomson Microelectronics, Inc., was a semigraphic microprocessor for video image control, encapsulated in a 40-pin DIP and used primarily in the Matra Alice 32, Matra Alice 90 and Philips VG5000 microcomputers. The EF9345 was ...

graphic chip, only capable of displaying alphanumeric and

semigraphic Text-based semigraphics or pseudographics is a primitive method used in early text mode video hardware to emulate raster graphics without having to implement the logic for such a display mode. There are two different ways to accomplish the emu ...

characters. * The

PC-8001 The is a line of personal computers developed for the Japanese market by NEC. The PC-8001 model was also sold in the United States and Canada as the PC-8001A. Original models of the NEC PC-8001B (or sometimes the NEC PC-8000) were also sold in so ...

managed to combine normal text with a full set of 256 text semigraphical "characters" in a 2×4 matrix; how the system distinguished the 8 bits used for "normal" fonts from the 8 bits needed for the text semigraphics is unclear. * One of the last video systems where text semigraphics were a useful option was the

Color Graphics Adapter The Color Graphics Adapter (CGA), originally also called the ''Color/Graphics Adapter'' or ''IBM Color/Graphics Monitor Adapter'', introduced in 1981, was IBM's first color graphics card for the IBM PC and established a de facto computer display ...

(CGA). This graphics adapter for early IBM-PCs only supported four colors in its high-resolution graphics mode, but in text mode it could display 16 different colors. Although the CGA adapter's font ROM did not contain all of the otherwise typical text semigraphics characters, it was still possible to create a 160 × 100 CGA text semigraphics mode using a semi-documented trick.

Semigraphical characters

Semigraphical characters are also characters in a font that are intended to give the impression that a system can support high resolution graphics, while in fact the system operates in text mode. Characters such as box-drawing characters, circles and dots, card symbols like ♠, ♣, ♥ and ♦, and "graphical building block"

geometric shapes Geometric Shapes is a Unicode block of 96 symbols at code point range U+25A0–25FF. U+25A0–U+25CF The BLACK CIRCLE is displayed when typing in a password field, in order to hide characters from a screen recorder or shoulder surfing. U+2 ...

such as triangles gave such systems that appearance. One of the first systems that used such characters, the canonical example that others followed, was the Commodore PET, which had many of them within its PETSCII font set. The original PET relied to such a degree on these characters that it printed them on its keyboard, as can be seen here, an example that other systems soon copied. Another good example of a system that relied on semigraphical characters is the venerable Sharp MZ80K, which had no high-resolution graphics, nor reprogrammable characters, but relied fully on an extended font set with many pseudo graphical characters. With these it was still possible to generate games that looked like the system had high-resolution graphics. Some of the systems that had a programmable font set, but did not have a real high resolution raster graphics hardware, came with default character sets to be uploaded in character set RAM, and these sets often incorporated the ideas mentioned here, although it was often also the case that dedicated semigraphical characters were defined as needed.

Systems that relied on semigraphical characters

Examples of systems that relied heavily on semigraphical characters for their graphics are: * The original

IBM PC The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first microcomputer released in the IBM PC model line and the basis for the IBM PC compatible de facto standard. Released on August 12, 1981, it was created by a team ...

with the

MDA MDA, mda, or ''variation'', may refer to: Places * Moldova, a country in Europe with the ISO 3166-1 country code MDA Politics * Meghalaya Democratic Alliance (2018), ruling coalition government in the Indian State of Meghalaya led by National Pe ...

offered no form of graphics other than the

of its default hardware code page

437 __NOTOC__ Year 437 ( CDXXXVII) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Aetius and Sigisvultus (or, less frequently, year 119 ...

. * The Commodore PET was one of the first systems to rely heavily on semigraphical characters, to get any form of graphics on screen (see PETSCII). * The

Sinclair Sinclair may refer to: Places * Lake Sinclair, near Milledgeville, Georgia * Sinclair, Iowa * Sinclair, West Virginia * Sinclair, Wyoming * Sinclair Mills, British Columbia * Sinclair Township, Minnesota * Sinclair, Manitoba People * Sin ...

and

ZX81 The ZX81 is a home computer that was produced by Sinclair Research and manufactured in Dundee, Scotland, by Timex Corporation. It was launched in the United Kingdom in March 1981 as the successor to Sinclair's ZX80 and designed to be a low-cost ...

relied on block graphics characters for a low-resolution graphics of 64×48 pixels black-and-white or 32×48 in black, white, and dithered gray as seen in the

ZX80 character set The ZX80 character set is the character encoding used by the Sinclair Research ZX80 microcomputer with its original 4K BASIC ROM. The encoding uses one byte per character for 256 code points. It has no relationship with previously established ones ...

and ZX81 character set. * The Mattel Aquarius relied completely on its character set for games, even though it was marketed through toy-shops. It never became a commercial success partly because of this limitation, which was outdated at the time (see Mattel Aquarius character set). * The

also used semigraphical characters in combination with block graphics (see Matsushita JR series character set). * The

Sharp MZ The Sharp MZ is a series of personal computers sold in Japan and Europe (particularly Germany and Great Britain) by Sharp beginning in 1978. History Although commonly believed to stand for "Microcomputer Z80", the term MZ actually has its ...

series of computers offered no high resolution or programmable characters, but did have a very complete set of semigraphical characters (see Sharp MZ character set). - and so still offered many visually nice games * The

32 and 90; and the

(see Thomson EF9345 character set). * The

Compukit UK101 The Compukit UK101 microcomputer (1979) is a kit clone of the Ohio Scientific Superboard II single-board computer, with a few enhancements for the UK market - notably replacing the 24×24 (add guardband kit to give 32×32) screen display with a ...

(clone of the popular Ohio Scientific superboard) also was a very early system that relied on its 256 characters set. * The text modes of later Apple II computers, beginning with the

Apple IIc The Apple IIc, the fourth model in the Apple II series of personal computers, is Apple Computer's first endeavor to produce a portable computer. The result was a notebook-sized version of the Apple II that could be transported from place to pl ...

and the enhanced version of the Apple IIe, supported the

MouseText MouseText is a set of 32 graphical characters designed by Bruce Tognazzini and first implemented in the Apple IIc. They were then retrofitted to the Apple IIe forming part of the Enhanced IIe upgrade. A slightly revised version was then released w ...

character set, which replaced flashing uppercase characters when enabled. Although these Apple systems did not rely on these character sets they did play a role in simulating GUI like graphics of their more advanced family members, while still in text mode.

References

{{reflist, refs= {{cite book , title=Proposal to add characters from legacy computers and teletext to the UCS , chapter=5. Graphic characters , work=Universal Multiple-Octet Coded Character Set , publisher=Terminals Working Group (TWG),

International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...

, author-first1=Doug , author-last1=Ewell , author-link1=Doug Ewell , author-first2=Rebecca G. , author-last2=Bettencourt , author-link2=Rebecca G. Bettencourt , author-first3=Ricardo , author-last3=Bánffy , author-first4=Michael , author-last4=Everson , author-link4=Michael Everson , author-first5=Eduardo Marín , author-last5=Silva , author-first6=Elias , author-last6=Mårtenson , author-first7=Mark , author-last7=Shoulson , author-first8=Shawn , author-last8=Steele , author-first9=Rebecca , author-last9=Turner , date=2019-01-04 , id=L2/19-25 , page=3 , url=http://www.unicode.org/L2/L2019/19025-terminals-prop.pdf , access-date=2021-01-11 , url-status=live , archive-url=https://web.archive.org/web/20201224013239/https://www.unicode.org/L2/L2019/19025-terminals-prop.pdf , archive-date=2020-12-24 , quote-page=3 , quote=The word "sextant" is used in this document, by analogy with "quadrant"—a term used for certain UCS characters since 1999—to refer to a semigraphics block consisting of six smaller blocks or "cells" arranged in two columns and three rows. In the teletext specification, characters in this group could be displayed either with the cells joined together, as with the existing quadrant characters, or with a narrow space between cells. A teletext emulator could interpret the control character U+001A ("separated graphics") to display space between cells, or U+0019 ("contiguous graphics") to revert to the default, joined appearance {{cite web , author-first=Ira , author-last=Goldklang , date=2015 , title=Graphic Tips & Tricks , url=http://www.trs-80.com/wordpress/zaps-patches-pokes-tips/graphics/ , access-date=2017-07-29 , url-status=live , archive-url=https://web.archive.org/web/20170729202445/http://www.trs-80.com/trs80-zaps-hardware-model4.htm , archive-date=2017-07-29 {{Cite web, url=https://www.unicode.org/charts/PDF/U25A0.pdf, title=Unicode block U25A0 contains geometric shapes {{Cite web, url=http://jayceland.com/LunchNStuff/Archives/2002905.html, title=JayceLand's Weekly Rochester Events #191: All White Sixel, website=jayceland.com {{Cite web , url=http://www.old-computers.com/museum/software.asp?t=2&c=330&st=1 , title=OLD-COMPUTERS.COM Museum ~ GALAKSIJA Galaksija software & screenshots , access-date=2014-01-27 , at=See the second image from above. The image shows small difference in height of some "pixel"s. {{Cite web, url=http://www.old-computers.com/museum/doc.asp?c=409&st=1, title=Description of TRS-80 block graphics Technical details ZX-81 character set and block graphics
/ref> {{Cite web, url=http://www.cs.unc.edu/~yakowenk/coco/text/semigraphics.html, title=CoCo Semi-graphics-6 display mode {{Cite web, url=http://www.bbcbasic.co.uk/bbcwin/manual/bbcwinh.html, title=R.T.Russell: BBC BASIC for Windows, website=www.bbcbasic.co.uk {{Citation , year=1983 , title=IBM PC XT Technical Reference , publisher=IBM , url=https://archive.org/details/IBMPCXTTechnicalReference1502237 , at=p. 1-142 , access-date=2018-08-24 {{Citation , year=1983 , title= Commodore C64 Manual: Commodore 64 Programmers Reference Guide , publisher=Commodore , page=379 , url=https://archive.org/details/Commodore_64_Programmers_Reference_Guide_1983_Commodore , access-date=2018-08-24 {{Cite web, url=http://www.old-computers.com/museum/computer.asp?c=174, title=old-computers.com Entry on the Sharp MZ80K mentions the lack of graphics capabilities {{Cite web, url=https://www.youtube.com/watch?v=MgBQH2PLHs4, title=Sharp MZ80K - BASE ZERO game., via=www.youtube.com {{Cite web, url=https://www.vdsteenoven.com/aquarius/, title=Mattel Aquarius Homecomputer system, website=www.vdsteenoven.com {{Cite web, url=http://old-computers.com/museum/software.asp?c=174&st=1, title=Games on the MZ-80K relied on its great set of semigraphical characters Computer graphic techniques Character sets Computer graphics data structures Graphics file formats Videotex

Block graphics

Examples of the use of block graphics

Semigraphical characters

Systems that relied on semigraphical characters

See also

References