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Semigraphics

Text-based semigraphics, pseudographics, or character graphics 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.

{{anchor|Squot|Sextant|Quadrant}}Block graphics
(CoCo), Laser 210 and Dragon 32/64 For character cells consisting of 8 vertical and 8 horizontal pixels (an 8 × 8 character), 264 ≈ 1019 characters would be needs to represent every possible combination of the 64 pixels. Instead, if the 8 × 8 character is divided into 2 × 2 "pixels" called quadrants, matrix of so-called squots (square dots) • Videotex and teletext systems used a 2 × 3 matrix with 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). Matra Alice 90 and Philips VG5000 were based on the Thomson EF9345 graphic chip, only capable of displaying alphanumeric and semigraphic characters. • The PC-8001 managed to combine normal text with a full set of 256 text semigraphical "characters" in a 2 × 4 matrix; the system distinguished the set of 256 semigraphics patterns from the 256-character set used for "normal" fonts via character attribute bytes. • One of the last video systems where text semigraphics were a useful option was the Color Graphics Adapter (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
'' has semigraphical characters indicated for easy entry 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 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 with the MDA offered no form of graphics other than the box-drawing characters of its default hardware code page 437. • 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 ZX80 and ZX81 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 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 Panasonic JR-200 also used semigraphical characters in combination with block graphics (see Matsushita JR series character set). • The Sharp MZ 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 Matra Alice 32 and 90; and the Philips VG5000 (see Thomson EF9345 character set). • The Compukit UK101 (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 and the enhanced version of the Apple IIe, supported the MouseText 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. ==See also==
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