GRASS (GRAphics Symbiosis System) was a programming language created to script vector graphics visual animations in 2D. GRASS was similar to the BASIC programming language in syntax, but added numerous instructions for specifying 2D object animation, including scaling, translation, rotation and color changes over time. It quickly became a hit with the artistic community who were experimenting with the new medium of computer graphics, and will remain most famous for its use by Larry Cuba to create the original "attacking the death star will not be easy" animation in Star Wars. A later version that was adapted to support raster graphics was known as ZGrass. A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. ... Example showing effect of vector graphics on scale: (a) original vector-based illustration; (b) illustration magnified 8x as a vector image; (c) illustration magnified 8x as a bitmap image. ... BASIC (Beginners All-purpose Symbolic Instruction Code) is a family of high-level programming languages. ... Computer graphics is a sub-field of computer science and is concerned with digitally synthesizing and manipulating visual content. ... Opening logo to the Star Wars films Star Wars is an epic science fantasy saga and fictional galaxy created by writer/producer/director George Lucas during the 1970s. ... Suppose the smiley face in the top left corner is an RGB bitmap image. ...

History

The original version of GRASS was developed by Tom DeFanti for his 1974 Ohio State University Ph.D. thesis. It was developed on a PDP-11/45 driving a Vector General 3DR display, and as the name implies, this was a purely vector graphics machine. GRASS included a number of vector-drawing commands, and could organize collections of them into a hierarchy, applying the various animation effects to whole "trees" of the image at once (stored in arrays). It was this version that was used for the Star Wars animation, if you re-watch this portion of the film you can see object trees popping into the image at various times. The Ohio State University (OSU) is a coeducational public research university in the state of Ohio. ... The PDP-11 was a 16-bit minicomputer sold by Digital Equipment Corp. ... Example showing effect of vector graphics versus raster graphics. ...

After graduation, DeFanti moved to the University of Illinois, Chicago Circle. There he joined up with Dan Sandin and together they formed the Circle Graphics Habitat (today known as the Electronic Visualization Laboratory, or EVL). Sandin had joined the university in 1971 and set about building what he thought of as the video version of a Moog synthesizer, known as the Sandin Image Processor, or IP. The IP was an analog computer which took two video inputs, mixed them, colored the results, and then re-created TV output. The University of Illinois at Chicago (UIC) is a public, state-supported research university. ... The Electronic Visualization Laboratory (EVL) is a cross-disciplinary research lab at the University of Illinois at Chicago. ... The term Moog (pronounced /moʊg/ to rhyme with vogue, not /muːg/) synthesizer can refer to any number of analog synthesizers designed by Dr. Robert Moog or manufactured by Moog Music, and is commonly used as a generic term for analog and digital music synthesisers. ... The Sandin Image Processor is usually introduced as the video equivalent of a Moog audio synthesizer. ...

DeFanti added the existing GRASS system as the input to the IP, creating the GRASS/Image Processor, which was used throughout the mid-1970s. In order to make the system more useful, DeFanti and Sandin added all sorts of "one-off" commands to the existing GRASS system, but these changes also made the language considerably more idiosyncratic. In 1977 another member of the Habitat, Nola Donato, re-designed many of GRASS's control structures into more general forms, resulting in the considerably cleaner GRASS3.

In 1977 DeFanti was introduced to Jeff Frederiksen, a chip designer working at Dave Nutting Associates. Nutting had been contracted by Midway, the videogame division of Bally, to create a standardized graphics driver chip. They intended to use it in most of their future arcade games, as well as a video game console they were working on which would later turn into the Astrocade. Midway was quite interested in seeing the GRASS language running on their system, and contracted DeFanti to port it to the platform. A number of people at the Habitat, as well as some from Nutting, worked on the project, which they referred to as the Z Box. GRASS3 running on it became Zgrass. The work would never be released by Midway, but the Circle would produce machines based on it as the Datamax UV-1. Four different video game consoles from different generations. ... The Astrocade was an early video game console and simple computer system designed by a team at Midway Manufacturing, the videogame division of Bally. ... The Datamax UV-1 was a pioneering computer designed by a group of computer graphics artists working at the University of Illinois, known as the Circle Graphics Habitat. ...

The Z-Box was a raster graphics machine, unlike the original GRASS systems, so while most of the GRASS3 style was maintained in Zgrass, it added a number of commands dedicated to raster images. This included an extensive set of bit block transfer commands in order to simulate sprites, something the hardware didn't include. Suppose the smiley face in the top left corner is an RGB bitmap image. ... Bit blit (bitblt, blitting etc. ... In computer graphics, a sprite is a two-dimensional image or animation that is integrated into a larger scene. ...

The last version of GRASS was RT/1, a port of GRASS to other platforms that divorced the language from the display model and allowed it to be ported to other platforms. Versions existed for DOS, Windows, SGI platform using OpenGL, HP-UX, AIX, Macintosh and Amiga. The language remains similar to the earlier versions, so the reason for the change of name is unclear. ‹ The template below has been proposed for deletion. ... Microsoft Windows is the name of several families of proprietary software operating systems by Microsoft. ... Silicon Graphics, Inc. ... OpenGL (Open Graphics Library) is a standard specification defining a cross-language cross-platform API for writing applications that produce 3D computer graphics (and 2D computer graphics as well). ... HP-UX (Hewlett Packard UniX) is Hewlett-Packards proprietary implementation of the Unix operating system, based on System V (initially System III). ... AIX (Advanced Interactive eXecutive) is a proprietary operating system developed by IBM based on UNIX System V. Before the product was ever marketed, the acronym AIX originally stood for Advanced IBM UNIX. AIX has pioneered numerous network operating system enhancements, introducing new innovations later adopted by Unix-like operating systems... The first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac. The Macintosh or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple Computer. ... The original Amiga 1000 (1985) with various peripherals The Amiga is a family of home/personal computers originally developed by Amiga Corporation as an advanced home entertainment and productivity machine. ...

It is perhaps the introduction of the fully graphical systems like Macromind Director that made a language like Zgrass fade away. Macromedia Director is a powerful media application created by Macromedia. ...

Description

Zgrass was based on a standard set of BASIC commands and used most of its syntax. Where Zgrass differed from BASIC was that all commands were in fact functions and returned values, similar to the C programming language. If there was no obvious return value it was expected that a function would return 1 if it succeeded, and 0 if it failed. For instance, the command PRINT PRINT 10 would be illegal in BASIC, but in Zgrass this would print 10 1, the 1 being the value returned by second PRINT, meaning "I successfully outputted the string '10'". In computer science, a subroutine (function, procedure, or subprogram) is a sequence of code which performs a specific task, as part of a larger program, and is grouped as one, or more, statement blocks; such code is sometimes collected into software libraries. ... C is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system. ...

Programs in Zgrass were referred to as macros, and stored as strings. Both of these oddities were deliberate, as Zgrass allowed any string to become a program. For instance, MYBOX="BOX 0,0,100,100,2" defines a string (no need for a $ as in BASIC) containing a snippet of Zgrass code. Simply typing MYBOX from that point on would run the command(s) inside. This feature can be used in place of the more traditional GOSUB command from BASIC, but has the added advantage of having a well defined name as opposed to an opaque line number. In addition the command remains a string, and can be manipulated at runtime with standard string operations.

Most BASIC interpreters of the era converted the input text into a tokenized version in which each of the commands was replaced by a single number (typically one byte long). This made the program run faster because it didn't have to continually decode the commands from the strings every time. Zgrass's use of string-based macros made this difficult, so they didn't bother with tokenization. Instead they included a compiler which could be used on any particular macro, speeding it up many times. Programs would often consist of a mix of compiled and uncompiled macros. An interpreter is a computer program that executes other programs. ... In computer science a byte is a unit of measurement of information storage, often containing eight bits. ... This article is about the computing term. ...

Line numbers were optional in Zgrass, and typically only appeared on lines that were the target of a GOTO. Most BASIC interpreters required line numbers for every line of code, but this was due to their use in the "line editor"–if you needed to edit that line, the only way to refer to it was by number. Zgrass used a more advanced full-screen editor that eliminated this need (as was the case for True BASIC). Zgrass allowed any string to act as a "line number", GOTO 10 and GOTO MARKER were both valid. Zgrass also included nameless branches, using the SKIP instruction, which would move forward or back a given number of lines. True BASIC is a fully structured variant of the BASIC programming language descended from Dartmouth BASIC – the original BASIC – invented by college professors John G. Kemeny and Thomas E. Kurtz. ...

In keeping with its original purpose as a graphics language, Zgrass included numerous commands for simple drawing. Zgrass's coordinate system was based on that of the original graphics chip that Nutting had designed, based on a 320x202 grid. The Astrocade, for some reason, used only half the resolution, a 160x101 display. To avoid potential mapping problems, the coordinate space's zero point was placed in the center of the screen. -160 to 160 were valid X locations, and -101 to 101 valid Y locations. For use on the Astrocade you used the positive locations only, whereas on the UV-1 the entire space was available.

Zgrass added a fairly complete set of array functions, as arrays are widely used in graphics. This included the ability to "capture" parts of the display into an array as a bitmap, which could then be manipulated as any other graphic item. This allowed Zgrass to include sprite-like functionality in the language, something the Nutting hardware did not include. Another feature the Astrocade did not include was the ability to process arrays with any reasonable speed, so the UV-1 included the Zilog supplied FPU for added performance. For the use of the term raster in radio regulation, see frequency raster. ... A floating point unit (FPU) is a part of a computer system specially designed to carry out operations on floating point numbers. ...

Zgrass included three priorities (called levels) that allowed macros to be run normally, or in foreground or background levels. This added a simple form of multitasking which was tremendously useful in an animation-oriented language. Game authors could place joystick-reading routines in a macro set to run in the background, and then the joystick would be read automatically whenever the current drawing macro completed. Functions placed in the foreground ran before either, and was often used for timers and other "low latency" needs. Zgrass included a TIMEOUT function that would call macros on a timed basis, making the implementation of timers very easy. In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is...

Zgrass also included a series of commands that "covered" CP/M, which allowed the disk to be accessed without exiting to the command prompt. You could easily save out macros to named files, and load them in the same way, allowing you to construct programs by loading up various macros from the disk into one large program. The commands also automatically made a backup copy of every save. Similar features were supported for cassette tape storage, but oddly the syntax was marred, disk commands were D-something, like DPUT while tape commands were something-TAPE, like PUTTAPE. It is not clear why this difference in syntax existed TPUT seems like a better solution, and PUT D filename even better. For the meaning of cassette in genetics, see cassette (genetics). ...

With programs constructed from randomly selected modules, Zgrass needed to have better control over its variables than BASIC. In BASIC all variables are "global", so if two subroutines both use the variable i (very common) then they could set each others values leading to hard to debug problems. Under Zgrass a programmer loading up two modules would almost certainly find that both used i as a loop counter, and thus could cause problems. To address this problem, Zgrass allowed one to use lowercase letters for variables, in which case the variable was local only to that macro. Oddly the examples provided with the language do not make widespread use of this feature, potentially confusing new programmers who might not be aware the feature even exists. Minuscule, or lower case, is the smaller form (case) of letters (in the Roman alphabet: a, b, c, ...). Originally alphabets were written entirely in majuscule (capital) letters which were spaced between well-defined upper and lower bounds. ...

Example

SINCURVE=[PROMPT "WHAT IS THE OFFSET?"
INPUT OFFSET
x=-160
angle=0
POINT OFFSET+x,SIN(angle)*80,3
angle=angle+2
IF (x=x+1)<159,SKIP -2]


This text creates a new macro called SINCURVE that can be called simply by typing SINCURVE into the command prompt, or from other macros or programs. SINCURVE uses two local variables, x and angle, as well as a global variable, OFFSET.

The PROMPT/INPUT is a modification of the original BASIC INPUT, which will not ask for the input if the user types it into the command line when calling the macro. In this case typing SINCURVE will result in the prompt appearing and the program waiting for input, whereas typing SINCURVE 30 will skip the prompt and OFFSET will automatically be assigned 30. This allows a single macro to be used both interactively and within a program as a function.

POINT is an example of one of the many graphics commands included in the Zgrass language. POINTrequires an X and Y location, as well as a color. In this example the user supplied OFFSET moves the x position of the curve on the screen, while the Y position is supplied by the trig function, suitably enlarged for display (in this case, 80 times). The color is supplied in the last input, and in this case is 3. The UV-1 used color registers, so 3 did not imply a particular color, but a color selected from the current palette. Wikibooks has a book on the topic of Trigonometry Trigonometry (from the Greek Trigona = three angles and metron = measure[1]) is a branch of mathematics which deals with triangles, particularly triangles in a plane where one angle of the triangle is 90 degrees (right angled triangles). ...

The IF is likewise interesting. It places an increment, (x=x+1), in front of the test, a feature not normally available in BASIC. In this case the IF is told to call SKIP -2 if true, which will move back two lines and can be used in place of a GOTO.

External links

• Bally Alley Miscellaneous Documentation - includes PDF versions of scans of the UV-1 Zgrass manual