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:''For{{about|the programming language|the GIS system of this name, see [[GRASS|Grass GIS]].''}}

'''GRASS''' (''GRAphics Symbiosis System'') wasis a [[programming language]] created to script visual[[2D animations incomputer graphics|2D]] [[vector graphics]] animations. 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 changesrotation over time. These functions were directly supported by the [[Vector General 3D]] [[graphics terminal]] GRASS was written for. It quickly became a hit with the artistic community who were experimenting with the new medium of [[computer graphics]], and will remainis most famous for its use by [[Larry Cuba]] to create the original "attacking the death[[Death starStar]] will not be easy" animation in ''[[Star Wars (film)|Star Wars]]'' (1977).

As part of a later partnership with [[Midway Games]], the language was ported to the Midway's [[Zilog Z80|Z80]]-based Z Box. This machine used [[raster graphic]]s and a form of [[Sprite (computer graphics)|sprites]], which required extensive changes to support, along with animating color changes. This version was known as '''ZGRASS'''.

'''GRASS''' (''GRAphics Symbiosis System'') was a [[programming language]] created to script 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]].

== History ==

===GRASS===

The original version of GRASS was developed by [[Tom DeFanti]] for his 1974 [[Ohio State University]] Ph.D. thesis.{{sfn|DeFanti|1980}} It was developed on a [[PDP-11]]/45 driving a [[Vector General 3D|Vector General 3DR]] display, and.{{sfn|DeFanti|1980}} asAs 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. It(stored wasin 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 timesarrays).{{sfn|DeFanti|1980}}

After graduation, DeFanti moved to the [[University of Illinois at Chicago|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 asbuilt 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. He described it as the video version of a [[Moog synthesizer]].{{sfn|DeFanti|1980}}

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'''.{{sfn|DeFanti|1980}}

[[Larry Cuba]]'s ''Star Wars'' work is based on semi-automated filming of a GRASS system running on a [[Vector General 3D]] terminal. The VG3D had internal hardware that performed basic transformations - scaling, rotation, etc. - in realtime without interacting with the computer. It is only during the times when new scenery is being presented that the much slower communications with the GRASS language takes place. This can be seen in the sequence, as the initial sections of the film show the [[Death Star]] being rotated and scaled very rapidly, while the later sections simulating flight down the trench requires new scenery to be paged in from GRASS "trees". These can be seen appearing in groups.

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]].

===ZGRASS and UV-1===

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 blit|bit block transfer]] commands in order to simulate [[sprite (computer science)|sprite]]s, something the hardware didn't include.

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 [[Video display controller|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 '''ZgrassZGRASS'''. The work would never be released by Midway, but the Circle would produce machines based on it as the [[Datamax UV-1]].{{sfn|DeFanti|1980}}

The Z-Box was a [[raster graphics]] machine, unlike the original GRASS systems, so while most of the GRASS3 style was maintained in ZgrassZGRASS, it added a number of commands dedicated to raster images. This included an extensive set of [[bit blit|bit block transfer]] commands in order to simulate [[sprite (computer science)|sprite]]s, something the hardware didn't include.{{sfn|DeFanti|1980}} The work would never be released by Midway, but the Circle would produce machines based on it as the [[Datamax UV-1]].

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]], [[Microsoft Windows|Windows]], [[Silicon Graphics|SGI]] platform using [[OpenGL]], [[HP-UX]], [[AIX operating system|AIX]], [[Apple Macintosh|Macintosh]] and [[Amiga]]. The language remains similar to the earlier versions, so the reason for the change of name is unclear.

===GRASS RT/1===

It is perhaps the introduction of the fully graphical systems like [[Macromind Director]] that made a language like Zgrass fade away.

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 [[MS-DOS]], [[Microsoft Windows|Windows]], [[Silicon Graphics|SGI]] platform using [[OpenGL]], [[HP-UX]], [[IBM AIX operating system|AIX]], [[AppleMac Macintosh(computer)|Macintosh]] and [[Amiga]]. The language remains similar to the earlier versions, so the reason for the change of name is unclear.

== Description ==

:''This description is based on the original Bally manuals as well as the ACM description.''{{sfn|DeFanti|Fenton|Donato|1978}}

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 [[function (programming)|function]]s and returned values, similar to the [[C (programming language)|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 <code>PRINT PRINT 10</code> would be illegal in BASIC, but in Zgrass this would print <code>10 1</code>, the 1 being the value returned by second <code>PRINT</code>, meaning "I successfully output the string '10'".

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, <code>MYBOX="BOX 0,0,100,100,2"</code> defines a string (no need for a $ on the variable as in [[Microsoft BASIC]]s) containing a snippet of Zgrass code. Simply typing <{{code>|MYBOX</code>}} from that point on would run the command(s) inside. This feature can be used in place of the more traditional <code>GOSUB</code> 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 in the form of a string, in memory and can be manipulated at runtime with standard string operations.

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 [[function (programming)|function]]s 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 <code>PRINT PRINT 10</code> would be illegal in BASIC, but in Zgrass this would print <code>10 1</code>, the 1 being the value returned by second <code>PRINT</code>.

Most BASIC [[interpreter (computer softwarecomputing)|interpreters]] of the era converted the input text into a ''[[Lexical analysis|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.

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, <code>MYBOX="BOX 0,0,100,100,2"</code> defines a string (no need for a $ as in BASIC) containing a snippet of Zgrass code. Simply typing <code>MYBOX</code> from that point on would run the command(s) inside. This feature can be used in place of the more traditional <code>GOSUB</code> 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.

Line numbers were optional in Zgrass, and typically only appeared on lines that were the target of a <code>GOTO</code>. Most BASIC interpreters required line numbers for every line of code, but this was due to their use in the "line editor"&ndash;if you needed to edit ''that''a particular 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", <{{code>|GOTO 10</code>}} and <{{code>|GOTO MARKER</code>}} were both valid. Zgrass also included nameless branches, using the <code>SKIP</code> instruction, which would move forward or back a given number of lines.

Most BASIC [[interpreter (computer software)|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.

Zgrass also included nameless branches, using the {{code|SKIP}} instruction, which would move forward or back a given number of lines. This is important in Zgrass as the line numbers were optional and different macros might make use of the same labels. For instance, some variation on {{code|LOOPSTART}} is likely to be found in many bits of code, and thus {{code|GOTO LOOPSTART}} might result in a name clash. Using {{code|SKIP}} avoided this possibility.

Line numbers were optional in Zgrass, and typically only appeared on lines that were the target of a <code>GOTO</code>. Most BASIC interpreters required line numbers for every line of code, but this was due to their use in the "line editor"&ndash;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", <code>GOTO 10</code> and <code>GOTO MARKER</code> were both valid. Zgrass also included nameless branches, using the <code>SKIP</code> instruction, which would move forward or back a given number of lines.

In keeping with its original purpose as a graphics language, Zgrass included numerous commands for simple drawing. Zgrass's coordinate system washad basedone onpoint thatfor ofeach thepixel originalin graphicsthe chiphigh-resolution thatmode of Nutting's hadgraphics designedchip, based ongiving a 320x202320×202 grid. The Astrocade, forby some reasondesign, usedcould only halfuse thethat chip's low-resolution mode, a 160x101160×101 display. To avoid potential mapping problems, the coordinate space's zero point was placed in the center of the screen. -&minus;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 directly include this feature. Another feature the Astrocade did not include was the ability to process arrays with any reasonable speed, so the UV-1 included thea Zilog supplied [[floating -point unit|FPU]] for added performance.

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 [[computer multitasking|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 <{{code>|TIMEOUT</code>}} function that would call macros on a timed basis, making the implementation of timers very easy.

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 [[cassetteCompact tapeCassette (data)|Compact Cassette]] storage, but oddly the syntax was marred,not parallel: disk commands were D-something, like <{{code>|DPUT</code>}}, whilebut tape commands were somethingnot T-TAPEsomething, like <{{code>PUTTAPE</code>. It is not clear why this difference in syntax existed <code>|TPUT</code>}}, seemsbut likerather a better solutionsomething-TAPE, andlike <{{code>PUT D ''filename''</CODE> even better|PUTTAPE}}.

With programs constructed from randomlyarbitrarily 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{{code|I}}, which is (very common)commonly used as a loop index variable, then they could set each othersother's values leadingwhich leads to hard -to -debug problems. Under Zgrass a programmer loading up two modules wouldcould almost certainlyeasily find that both used i{{code|I}} as a loop counter, and thuswhich could cause problems. To address this problemissue, Zgrass allowedconsidered onevariables tonamed usewith [[lowercase]] letters forto variablesbe local only to that macro, inso which{{code|I}} caseand the{{code|i}} variablewere wasdifferent localvariables, onlyglobal toand thatlocal macrorespectively. Oddly, their ownthe examples provided with the language do not make muchwidespread useduse of this feature, althoughpotentially itconfusing shouldnew haveprogrammers beenwho suggestedmight asnot thebe standardaware methodthe forfeature naming variablesexists.

== Example ==

{{sxhl|2=basic|1=<nowiki/>

SINCURVE=[PROMPT "WHAT IS THE OFFSET?"<br>

INPUT OFFSET<br>

x=-160<br>

angle=0<br>

POINT OFFSET+x,SIN(angle)*80,3<br>

angle=angle+2<br>

IF (x=x+1)<159,SKIP -2]<br>

}}

This example shows several of the novel features of Zgrass. This text creates a new macro called <code>SINCURVE</code> that can be called simply by typing <code>SINCURVE</code> into the command prompt, or from other macros or programs. SINCURVE uses two local variables, <var>x</var> and <var>angle</var>, as well as a global variable, <var>OFFSET</var>.

The <code>PROMPT</code>/<code>INPUT</code> is a modification of the original BASIC <code>INPUT</code> which will not ask for the input if the user types it into the command line when calling the macro. In this case, typing <code>SINCURVE</code> will result in the prompt appearing and the program waiting for input, whereas typing <code>SINCURVE 30</code> 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.

<code>

SINCURVE=[PROMPT "WHAT IS THE OFFSET?"<br>

INPUT OFFSET<br>

x=-160<br>

angle=0<br>

POINT OFFSET+x,SIN(angle)*80,3<br>

angle=angle+2<br>

IF (x=x+1)<159,SKIP -2]<br>

</code>

<code>POINT</code> is an example of one of the many graphics commands included in the Zgrass language. <code>POINT</code> requires an X and Y ___location, as well as a color. In this example, the user supplied <code>OFFSET</code> moves the x position of the curve on the screen, while the Y position is supplied by the [[trigonometry|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.

This example shows several of the novel features of Zgrass. This text creates a new macro called <code>SINCURVE</code> that can be called simply by typing <code>SINCURVE</code> 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 <code>PROMPT</code>/<code>INPUTIF</code> is alikewise modificationnotable. ofIt theplaces originalan BASICincrement, <code>INPUT(x=x+1)</code>, whichin willfront not ask forof the inputtest, ifa thefeature usernot typesnormally itavailable intoin the command line when calling the macroBASIC. In this case typing <code>SINCURVE</code> will result in the promptIF appearingis andtold the program waiting for input, whereasto typingcall <code>SINCURVESKIP 30-2</code> willif skiptrue, the prompt and OFFSETwhich will automaticallymove beback assignedtwo 30.lines Thisand allows a single macro tocan be used bothin interactivelyplace and withinof a program as a function. Of course an <code>IFGOTO</code>, wrappedas aroundthere theis <code>INPUT</code>no wouldline work just asnumber welltarget.

==Notes==

<code>POINT</code> is an example of one of the many graphics commands included in the Zgrass language. <code>POINT</code>requires an X and Y ___location, as well as a color. In this example the user supplied <code>OFFSET</code> 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.

{{reflist|group=notes}}

==References==

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

===Citations===

{{reflist}}

==External links=Bibliography===

{{refbegin}}

*[http://www.classicgaming.com/ballyalley/misc_docs/misc_docs.html Bally Alley Miscellaneous Documentation] - includes PDF versions of scans of the UV-1 Zgrass manual

* {{cite book |first1=Thomas |last1=DeFanti |first2=Jay |last2=Fenton |first3=Nola |last3=Donato |title=Proceedings of the 5th annual conference on Computer graphics and interactive techniques |chapter=BASIC Zgrass—a sophisticated graphics language for the Bally Home Library Computer |chapter-url=http://dl.acm.org/citation.cfm?id=807366 |publisher=ACM SIGGRAPH Computer Graphics |volume=12 |issue=3 |date=August 1978 |pages=33–37 |doi=10.1145/800248.807366 |isbn=9781450379083 |s2cid=8014940 }}

* {{cite magazine |first=Thomas |last=DeFanti |url=https://archive.org/details/byte-magazine-1980-11-rescan/page/n91/mode/2up |title=Language Control Structures for Easy Electronic Visualization |magazine=BYTE |date=November 1980 }}

{{refend}}

{{BASIC}}

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