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Thread: One night fun - Script language

  1. #1

    One night fun - Script language

    Yesterday night I read an article about writing a script language and decided to give it a try. When I suddenly realised it's over 4 A.M., I decided it's time to sleep... Still, as for the first time coding something like this, it turned out quite well, I daresay.

    Contains nothing more than text drawing, variable handling, ifs, repeat and label+goto, but if someone has too much spare time - what do I care, check it out.

    Download: 'ere
    Thing requires SDL, SDL_ttf and SDL_gfx. Linux and Win32. Usage: ./parser < scriptfile

    Code:
    A short guide:
    - One command per line
    - All fields separated by a space
    - Commands are case-sensitive, must be in lowercase 
    
    Commands:
    windowsize W H - create a window with given size
    drawtext X Y COL TXT - print TXT at X,Y with COL color. Variables can be printed too.
    clrscr COL - fill the screen with given color
    line XA YA XB YB COL ALPHA - draw a line between points. Alpha is optional.
    rect XA YA XB YB COL ALPHA - fill a rectangle with color. Alpha is optional.
    circle XA YA XB YB RAD COL ALPHA - draw a filled circle. Alpha is optional.
    trigon XA YA XB YB XC YC COL ALPHA - draw a trigon. Alpha is optional.
    random VAR MIN MAX - assign a random value in range (MIN - MAX) to VAR. 
                         If Min is ommited, range is (0 - MAX-1). 
                         If both are ommited, range is (0, 100).
    updategfx - self-explanatory
    autoupdate on/off - turn on/off automatic updategfx call after every command
    delay TIME - sleep for TIME miliseconds
    windowname TXT - set TXT for window name
    quit - halt the whole thing
    
    Declaring an integer: int NAME VALUE
    Referencing an integer: $NAME
    Freeing an integer: trash $NAME
    Assigning a value: $NAME := VALUE
    If no value is specified, variables are set to 0 on declaration. If a variable is not assigned, referencing it will return 0. If a variable name is in use, declaring a new variable shadows the old one (making it completely inaccesible!) until the new one is trashed.
    
    Math expressions must be put in brackets - [VAL1 OPER VAL2]. No spaces between values and brackets!
    Operator list:
    + - * /
    % modulo
    ^ power
    & | X and or xor
    _ cut off modulo VAL2 (8 _ 3 is 6) 
    
    VALs can be variables, expressions or constants. Hex constants can be written like this: #HEXVAL.
    Example: $VAR := [[$POS + 50] _ #20]   
    
    You can also use the short operators:
    += -= *= /= %= ^= &= |= X= _= 
    
    Conditionals:
    if VAL1 OPER VAL2
       command
       else
       command
       fi
    
    Loop:
    repeat
    command
    until VAL1 OPER VAL2
    
    Boolean operators:
    = < > >= <= <>
    &= all VAL2 bits are set in VAL1
    _= VAL1 is divisable by VAL2
    Boolean expressions not implemented. ([$A - $B] = [$B - $C] is possible, but not [$A > $B] = [$B > $C]) 
    
    Procedures - declaration:
    proc NAME
         some code here
    corp
    
    Procedures - calling:
    call NAME ARG ARG ARG ARG (...)
    
    Arguments can be retrieved inside a function using $ARG:X: variables, where :X: is the argument number, beginning from 0. Note that procedure declaration does not specify its argcount - amount of arguments passed is left solely to the decision of the caller. The aforementioned amount is stored in the $ARG? variable (yes, with the qoutation mark). You can use the return VAL command to force quit a procedure and, optionally, return a value. It will be available in the $RESULT variable. All variable handling is done in the same global context, so you can access all variables normally - but You also must remember to trash all variables created by a procedure. ARGs are trashed automatically when a procedure ends and should NOT be freed manually, as automatic trash will still occur, corrupting the variable set. (Easily noticeable in a recursive procedure).
    
    Example:
    proc power
         if $ARG1 = 0
            return 1
            fi
         if $ARG1 _= 2
            call power $ARG0 [$ARG1 / 2]
            return [$RESULT * $RESULT]
            fi
         call power $ARG0 [$ARG1 - 1]
         return [$ARG0 * $RESULT]
    corp
    (Tested to work, works circa 10x slower than the built-in ^ operator.)
    
    The parser itself creates and updates seven variables.
    $MOUSEX - mouse position
    $MOUSEY - as above
    $CLICK - 0 for no click, 1 - left button, 2 - middle, 3 - right
    $CLICKX - click position
    $CLICKY - as above
    $TICKS - time running (in ms)
    $QUITREQUEST - when the user presses the "Close" button, this is set to 1
    I think that's all. A few sample scripts are included.
    Last edited by Super Vegeta; 02-02-2012 at 12:38 AM.

  2. #2
    Co-Founder / PGD Elder WILL's Avatar
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    Neat!

    I remember my first game 'script' I made up for my top-down space shooter. Never released the game/engine (not even as an alpha) but it was fun to make. The idea of mine was to script events or triggers within the level/mission. Idea being that you could script each mission you player, much like the old X-Wing level editors, only in text script. I may consider going back to doing something like that in a future project. Maybe something for the iPad.
    Jason McMillen
    Pascal Game Development
    Co-Founder





  3. #3
    Nice work. The simpler, the better. I like it.

    Some years ago I did an scripting engine based in FORTH, but I never used it. Actually it was very ugly and scripts were dirty; anyway it was funny and I learned a lot.
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  4. #4
    Gave it some extra work. Added drawing primitives (easy), but mostly - procedures. Took me quite a while to convey a way to make it all work, but I am very satisfied with the result. All necessary info was updated in the first post.

  5. #5
    PGD Staff code_glitch's Avatar
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    Damn.... This sure beats the config file based scripts I feed into my engines.... tut tut tut. And it has procedures to boot! Thats a lot of features for a small one night project
    I once tried to change the world. But they wouldn't give me the source code. Damned evil cunning.

  6. #6
    Well, as seen from the post above, procedures were added later, the first, truly one-night project had label+goto. But I'm glad it has found some appreciation.

    Hm, since PGM4 still isn't around, maybe I could write an article on this...

  7. #7
    Nice work Super Vegeta
    I remember fondly my first scripting language a few years ago...it worked ok, but could have been written better LOL
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