Block graphics

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Block graphics on the home computer C64

A block graphic is a graphic made up of characters specially designed for this purpose.

On many home computers of the late 1970s and early 1980s, individual screen pixels could not be controlled directly; rather, the graphics chip read the pixels to be output itself from a character set - ROM , see also character generator . A graphic output in today's sense was therefore impossible. In order to allow a restricted form of the graphic display, the developers included special characters in the font, which for example represent a line, a corner or an area filled with a pattern. The character set of the C64 ( see also CBM-ASCII ) and the VGA cards (see code page 437 ) also contained such characters for displaying block graphics. Today you can find something similar in the Unicode standard, for example the Unicode block frame drawing (U + 2500..U + 257F) and the subsequent Unicode block block elements . Some programs that run in a terminal emulation also use block graphics.

If necessary, block graphics could also be used to display single-point graphics, but in a much lower resolution. The Commodore 8-bit computers had all 16 variants of characters in their PETSCII character set in order to be able to display a 2 × 2 dot matrix (ie "quarter box") for each character position. With a character resolution of 40 × 25 or 80 × 25, the point resolutions were modest 80 × 50 and 160 × 50. The Tandy TRS-80 Model 1 offered graphic symbols with a 2x3 matrix with a character resolution of 64 × 16, which resulted in a point resolution of 128 × 48. This was enough to implement the first version of Sublogic's Flight Simulator . In contrast to Commodore, the graphics were also supported by corresponding basic commands. The Sinclair ZX-80/81 computers also offered 2x2 graphics with basic support.

The Commodore computers mentioned also offered graphic characters with which you could either use the full point resolution in the x or y direction, but in the other coordinate direction you were then limited to the character resolution. Specifically, it was possible to achieve representations of 40 × 200 or 80 × 200 and 320 × 25 or 640 × 25. The 80 × 200 resolution in particular offered practical help, e.g. B. when examining the details of mathematical curves.

In addition, most fonts contained by home computers still playing card symbols and other characters in computer games were useful. On the other hand, the graphic symbols in the IBM PC were designed more for frame and window design, clearly in the direction of office applications .

Block graphics are not to be confused with ASCII art , in which special characters outside of the characters defined in the ASCII standard are explicitly dispensed with in order to achieve a platform-independent display. Block graphic characters, on the other hand, were different depending on the manufacturer (see above).