Access to the keyboard and to textual windows.

§1. Rocks. These are unique ID codes used to mark resources; think of them as inedible cookies. 

Constant GG_MAINWIN_ROCK        201;
Constant GG_STATUSWIN_ROCK      202;
Constant GG_QUOTEWIN_ROCK       203;
Constant GG_SAVESTR_ROCK        301;
Constant GG_SCRIPTSTR_ROCK      302;
#Ifdef COMMAND_STREAM;
Constant GG_COMMANDWSTR_ROCK    303;
Constant GG_COMMANDRSTR_ROCK    304;
#Endif;
Constant GG_SCRIPTFREF_ROCK     401;
Constant GG_FOREGROUNDCHAN_ROCK 410;
Constant GG_BACKGROUNDCHAN_ROCK 411;

§2. Transcript support. This is a mode in which the transcript of text in the main window is being written out to an external file.

VM_TranscriptIsOn tests whether this mode is on. VM_TranscriptOn should be called only if it is off, and tries to turn it on, returning true or false according to whether or not it succeeds. VM_TranscriptOff should be called only if scripting is on: this always succeeds. 

Global gg_scriptfref = 0;
Global gg_scriptstr = 0;

[ VM_TranscriptIsOn;
    if (gg_scriptstr) rtrue;
    rfalse;
];

[ VM_TranscriptOn;
    while (true) {
        if (gg_scriptfref == 0) {
            gg_scriptfref = glk_fileref_create_by_prompt($102, $05, GG_SCRIPTFREF_ROCK);
            if (gg_scriptfref == 0) rfalse;
        }
        stream_open_file
        gg_scriptstr = glk_stream_open_file_uni(gg_scriptfref, $05, GG_SCRIPTSTR_ROCK);
        if (gg_scriptstr == 0) {
            Could not open selected file; select again
            glk_fileref_destroy(gg_scriptfref);
            gg_scriptfref = 0;
            continue;
        }
        glk_window_set_echo_stream(gg_mainwin, gg_scriptstr);
        rtrue;
    }
];

[ VM_TranscriptOff;
    glk_stream_close(gg_scriptstr, 0); stream_close
    gg_scriptstr = 0;
    rtrue;
];

§3. Dictionary Parameters. Each word in the dictionary data structure has two metadata fields, known for traditional Inform 6 reasons as "dictionary parameters 1 and 2". Number 1 is a bitmap: some of the higher bits are written by the I6 compiler only when certain compile options are set, but they will be for the code which I7 generates. Bit 6 is currently never written by I6; bit 5, marking singular nouns, is never used by this parser.

(For speed reasons, reading of DICTPAR1_NOUN and DICTPAR1_PREP is done directly by ParserKit rather than by calling functions here.) 

Constant DICT_ENTRY_BYTES = 12+DICT_WORD_SIZE*WORDSIZE;
Constant #dict_par1 = DICT_WORD_SIZE*WORDSIZE+4+1;
Constant #dict_par2 = DICT_WORD_SIZE*WORDSIZE+4+3;

Constant DICTPAR1_VERB = 1;
Constant DICTPAR1_META = 2;
Constant DICTPAR1_PLURAL = 4;
Constant DICTPAR1_PREP = 8;
Constant DICTPAR1_SING = 16;
Constant DICTPAR1_BIT6 = 32;
Constant DICTPAR1_TRUNC = 64;
Constant DICTPAR1_NOUN = 128;

[ WordMarkedAsVerb w;
    if ((w) && ((w->#dict_par1) & DICTPAR1_VERB)) rtrue;
    rfalse;
];

[ WordMarkedAsMeta w;
    if ((w) && ((w->#dict_par1) & DICTPAR1_META)) rtrue;
    rfalse;
];

[ WorkMarkedAsUntruncatedPlural w b;
    if (w) {
        b = w->#dict_par1;
        if (b & DICTPAR1_TRUNC) rfalse;
        if (b & DICTPAR1_PLURAL) rtrue;
    }
    rfalse;
];

§4. Extracting Verb Numbers. A long tale of woe lies behind the following. Infocom games stored verb numbers in a single byte in dictionary entries, but they did so counting downwards, so that verb number 0 was stored as 255, 1 as 254, and so on. Inform followed suit so that debugging of Inform 1 could be aided by using the then-available tools for dumping dictionaries from Infocom story files; by using the Infocom format for dictionary tables, Inform's life was easier.

But there was an implicit restriction there of 255 distinct verbs (not 256 since not all words were verbs). When Glulx raised almost all of the Z-machine limits, it made space for 65535 verbs instead of 255, but it appears that nobody remembered to implement this in I6-for-Glulx and the Glulx form of the I6 library. This was only put right in March 2009, and the following routine was added to concentrate lookups of this field in one place. 

[ DictionaryWordToVerbNum w verbnum;
    w = w + #dict_par2 - 1;
    @aloads w 0 verbnum;
    verbnum = $ffff-verbnum;
    return verbnum;
];

§5. Variables and Arrays. 

Array gg_event --> 4;
Array gg_arguments buffer 28;
Global gg_mainwin = 0;
Global gg_statuswin = 0;
Global gg_quotewin = 0;
Global gg_savestr = 0;
#Ifdef COMMAND_STREAM;
Global gg_commandstr = 0;
Global gg_command_reading = 0;      true if gg_commandstr is being replayed
#Endif;
Global gg_foregroundchan = 0;
Global gg_backgroundchan = 0;

Constant INPUT_BUFFER_LEN = 260;    No extra byte necessary
Constant MAX_BUFFER_WORDS = 20;
Constant PARSE_BUFFER_LEN = 61;

Array  buffer   --> INPUT_BUFFER_LEN;
Array  buffer2  --> INPUT_BUFFER_LEN;
Array  buffer3  --> INPUT_BUFFER_LEN;
Array  parse     --> PARSE_BUFFER_LEN;
Array  parse2    --> PARSE_BUFFER_LEN;

§6. Dictionary words. This tests whether an address is probably that of a dictionary word. It's used only for debugging output, so the false positives here really do not matter. 

[ VM_ProbablyDictionaryAddress addr;
    if (addr->0 == $60) rtrue;
    rfalse;
];

§7. Keyboard Input. The VM must provide three routines for keyboard input:

There are elaborations to do with mouse clicks, but this isn't the place to document all of that. 

[ VM_KeyChar win done res ix jx ch;
    jx = ch; squash compiler warnings
    if (win == 0) win = gg_mainwin;
#Ifdef COMMAND_STREAM;
    if (gg_commandstr ~= 0 && gg_command_reading ~= false) {
        done = glk_get_line_stream(gg_commandstr, gg_arguments, 31);
        if (done == 0) {
            glk_stream_close(gg_commandstr, 0);
            gg_commandstr = 0;
            gg_command_reading = false;
            fall through to normal user input.
        } else {
            Trim the trailing newline
            if (gg_arguments->(done-1) == 10) done = done-1;
            res = gg_arguments->0;
            if (res == '\') {
                res = 0;
                for (ix=1 : ix<done : ix++) {
                    ch = gg_arguments->ix;
                    if (ch >= '0' && ch <= '9') {
                        @shiftl res 4 res;
                        res = res + (ch-'0');
                    } else if (ch >= 'a' && ch <= 'f') {
                        @shiftl res 4 res;
                        res = res + (ch+10-'a');
                    } else if (ch >= 'A' && ch <= 'F') {
                        @shiftl res 4 res;
                        res = res + (ch+10-'A');
                    }
                }
            }
            jump KCPContinue;
        }
    }
#Endif;
    done = false;
    glk_request_char_event(win);
    while (~~done) {
        glk_select(gg_event);
        switch (gg_event-->0) {
          evtype_CharInput:
            if (gg_event-->1 == win) {
                res = gg_event-->2;
                done = true;
            }
        }
    }
#Ifdef COMMAND_STREAM;
    if (gg_commandstr ~= 0 && gg_command_reading == false) {
        if (res < 32 || res >= 256 || (res == '\' or ' ')) {
            glk_put_char_stream(gg_commandstr, '\');
            done = 0;
            jx = res;
            for (ix=0 : ix<8 : ix++) {
                @ushiftr jx 28 ch;
                @shiftl jx 4 jx;
                ch = ch & $0F;
                if (ch ~= 0 || ix == 7) done = 1;
                if (done) {
                    if (ch >= 0 && ch <= 9) ch = ch + '0';
                    else                    ch = (ch - 10) + 'A';
                    glk_put_char_stream(gg_commandstr, ch);
                }
            }
        } else {
            glk_put_char_stream(gg_commandstr, res);
        }
        glk_put_char_stream(gg_commandstr, 10); newline
    }
  .KCPContinue;
#Endif;
    return MapGlkKeyCodeToUnicode(res);
];

[ VM_KeyDelay tenths  key done;
    glk_request_char_event(gg_mainwin);
    glk_request_timer_events(tenths*100);
    while (~~done) {
        glk_select(gg_event);
        if (gg_event-->0 == evtype_Timer or evtype_CharInput) {
            key = gg_event-->2;
            done = true;
        }
    }
    glk_cancel_char_event(gg_mainwin);
    glk_request_timer_events(0);
    return key;
];

Array UnicodeWhitespace --> 133 160 5760 8232 8233 8239 8287 12288;
Constant UnicodeWhitespaceLen = 8;

[ VM_ReadKeyboard  a_buffer a_table done ix chr;
#Ifdef COMMAND_STREAM;
    if (gg_commandstr ~= 0 && gg_command_reading ~= false) {
        done = glk_get_line_stream_uni(gg_commandstr, a_buffer+WORDSIZE,
            (INPUT_BUFFER_LEN-1)-1);
        if (done == 0) {
            glk_stream_close(gg_commandstr, 0);
            gg_commandstr = 0;
            gg_command_reading = false;
        } else {
            Trim the trailing newline
            if ((a_buffer+WORDSIZE)-->(done-1) == 10) done = done-1;
            a_buffer-->0 = done;
            VM_Style(INPUT_VMSTY);
            glk_put_buffer_uni(a_buffer+WORDSIZE, done);
            VM_Style(NORMAL_VMSTY);
            print "^";
            jump KPContinue;
        }
    }
#Endif;
    done = false;
    glk_request_line_event_uni(gg_mainwin, a_buffer+WORDSIZE, INPUT_BUFFER_LEN-1, 0);
    while (~~done) {
        glk_select(gg_event);
        switch (gg_event-->0) {
          evtype_LineInput:
            if (gg_event-->1 == gg_mainwin) {
                a_buffer-->0 = gg_event-->2;
                done = true;
            }
        }
    }
    Manually echo the command if required
    if (BasicInformKit`MANUAL_INPUT_ECHOING_CFGF && Cached_Glk_Gestalts-->gestalt_LineInputEcho) {
        glk_set_style(style_Input);
        glk_put_buffer_uni(a_buffer + WORDSIZE, a_buffer-->0);
        glk_set_style(style_Normal);
        glk_put_char(10); newline
    }
#Ifdef COMMAND_STREAM;
    if (gg_commandstr ~= 0 && gg_command_reading == false) {
        glk_put_buffer_stream(gg_commandstr, a_buffer+WORDSIZE, a_buffer-->0);
        glk_put_char_stream(gg_commandstr, 10); newline
    }
  .KPContinue;
#Endif;

    for ( ix = 1 : ix <= (a_buffer-->0) : ix++ ) {
      chr = a_buffer-->ix;
      if ((chr <= 32) || (((chr >= 8192) && (chr <= 8202))))
        a_buffer-->ix = 32;
      else {
        @binarysearch chr WORDSIZE UnicodeWhitespace WORDSIZE UnicodeWhitespaceLen 0 0 chr;
    if (chr) a_buffer-->ix = 32;
      }
    }
    if (a_table) {
        VM_Tokenise(a_buffer, a_table);
    }
    It's time to close any quote window we've got going.
    if (gg_quotewin) {
        glk_window_close(gg_quotewin, 0);
        gg_quotewin = 0;
        Quote_Window.glk_ref = 0;
    }
];

§8. Buffer Functions. A "buffer", in this sense, is an array containing a stream of characters typed from the keyboard; a "parse buffer" is an array which resolves this into individual words, pointing to the relevant entries in the dictionary structure. Because each VM has its own format for each of these arrays (not to mention the dictionary), we have to provide some standard operations needed by the rest of the template as routines for each VM.

VM_CopyBuffer(to, from) copies one buffer into another.

VM_PrintBuffer(buf) prints a buffer.

VM_PrintToBuffer(buf, len, a, b, c) prints something into a buffer.

VM_Tokenise(buff, parse_buff) takes the text in the buffer buff and produces the corresponding data in the parse buffer parse_buff — this is called tokenisation since the characters are divided into words: in traditional computing jargon, such clumps of characters treated syntactically as units are called tokens.

LTI_Insert is documented in the DM4 and the LTI prefix stands for "Language To Informese": it's used only by translations into non-English languages of play, and is not called in the template. 

[ VM_CopyBuffer bto bfrom i;
    for (i=0: i<INPUT_BUFFER_LEN: i++) bto-->i = bfrom-->i;
];

[ VM_PrintBuffer buf  buf_inner len i;
    len = (buf-->0) + 1;
    for (i = 1: i < len: i++) {
        print (char) buf-->i;
    }
];

[ VM_PrintToBuffer buf len a b c;
    if (b) {
        if (metaclass(a) == Object && a.#b == WORDSIZE
            && metaclass(a.b) == String)
            buf-->0 = Glulx_PrintAnyToArrayUni(buf+WORDSIZE, len, a.b);
        else if (metaclass(a) == Routine)
            buf-->0 = Glulx_PrintAnyToArrayUni(buf+WORDSIZE, len, a, b, c);
        else
            buf-->0 = Glulx_PrintAnyToArrayUni(buf+WORDSIZE, len, a, b);
    }
    else if (metaclass(a) == Routine)
        buf-->0 = Glulx_PrintAnyToArrayUni(buf+WORDSIZE, len, a, b, c);
    else
        buf-->0 = Glulx_PrintAnyToArrayUni(buf+WORDSIZE, len, a);
    if (buf-->0 > len) buf-->0 = len;
    return buf-->0;
];

Constant LOWERCASE_BUF_SIZE = 2*DICT_WORD_SIZE;
Array gg_lowercasebuf --> LOWERCASE_BUF_SIZE;

[ VM_Tokenise buf tab
    cx numwords len bx ix wx wpos wlen val res dictlen ch bytesperword uninormavail;
    len = buf-->0;
    buf = buf+WORDSIZE;

    First, split the buffer up into words. We use the standard Infocom
    list of word separators (comma, period, double-quote).

    cx = 0;
    numwords = 0;
    while (cx < len) {
        while (cx < len && buf-->cx == ' ') cx++;
        if (cx >= len) break;
        bx = cx;
        if (buf-->cx == '.' or ',' or '"') cx++;
        else {
            while (cx < len && buf-->cx ~= ' ' or '.' or ',' or '"') cx++;
        }
        tab-->(numwords*3+2) = (cx-bx);
        tab-->(numwords*3+3) = 1+bx;
        numwords++;
        if (numwords >= MAX_BUFFER_WORDS) break;
    }
    tab-->0 = numwords;

    Now we look each word up in the dictionary.

    dictlen = #dictionary_table-->0;
    bytesperword = DICT_WORD_SIZE * WORDSIZE;
    uninormavail = Cached_Glk_Gestalts-->gestalt_UnicodeNorm;

    for (wx=0 : wx<numwords : wx++) {
        wlen = tab-->(wx*3+2);
        wpos = tab-->(wx*3+3);

        Copy the word into the gg_tokenbuf array, clipping to DICT_WORD_SIZE
        characters and lower case. We'll do this in two steps, because
        lowercasing might (theoretically) condense characters and allow more
        to fit into gg_tokenbuf.
        if (wlen > LOWERCASE_BUF_SIZE) wlen = LOWERCASE_BUF_SIZE;
        cx = wpos - 1;
        for (ix=0 : ix<wlen : ix++) {
            ch = buf-->(cx+ix);
            gg_lowercasebuf-->ix = ch;
        }
        wlen = glk_buffer_to_lower_case_uni(gg_lowercasebuf, LOWERCASE_BUF_SIZE, wlen);
        if (uninormavail) {
            Also normalize the Unicode — combine accent marks with letters
            where possible.
            wlen = glk_buffer_canon_normalize_uni(gg_lowercasebuf, LOWERCASE_BUF_SIZE, wlen); buffer_canon_normalize_uni
        }
        if (wlen > DICT_WORD_SIZE) wlen = DICT_WORD_SIZE;
        for (ix=0: ix<wlen : ix++) {
            gg_tokenbuf-->ix = gg_lowercasebuf-->ix;
        }
        for (: ix<DICT_WORD_SIZE : ix++) gg_tokenbuf-->ix = 0;

        val = #dictionary_table + WORDSIZE;
        @binarysearch gg_tokenbuf bytesperword val DICT_ENTRY_BYTES dictlen 4 1 res;
        tab-->(wx*3+1) = res;
    }
];

[ LTI_Insert i ch  b y;

    Protect us from strict mode, as this isn't an array in quite the
    sense it expects
    (This is not an issue now that buffer is a word array, but I'm
    keeping the alias.)
    b = buffer;

    Insert character ch into buffer at point i.
    Being careful not to let the buffer possibly overflow:
    y = b-->0;
    if (y > INPUT_BUFFER_LEN) y = INPUT_BUFFER_LEN;

    Move the subsequent text along one character:
    for (y=y+1 : y>i : y--) b-->y = b-->(y-1);
    b-->i = ch;

    And the text is now one character longer:
    if (b-->0 < INPUT_BUFFER_LEN) (b-->0)++;
];

§9. Dictionary Functions. Again, the dictionary structure is differently arranged on the different VMs. This is a data structure containing, in compressed form, the text of all the words to be recognised by tokenisation (above). In I6 for Glulx, a dictionary word is represented at run-time by its record's address in the dictionary.

VM_InvalidDictionaryAddress(A) tests whether A is a valid record address in the dictionary data structure. In Glulx, dictionary records might in theory be anywhere in the 2 GB or so of possible memory, but we can rule out negative addresses. (This allows \(-1\), say, to be used as a value meaning "not a valid dictionary word".)

VM_DictionaryAddressToNumber(A) and VM_NumberToDictionaryAddress(N) convert between word addresses and their run-time representations: since, on Glulx, they are the same, these are each the identity function. 

[ VM_InvalidDictionaryAddress addr;
    if (addr < 0) rtrue;
    rfalse;
];

[ VM_DictionaryAddressToNumber w; return w; ];
[ VM_NumberToDictionaryAddress n; return n; ];

Array gg_tokenbuf --> DICT_WORD_SIZE;

[ GGWordCompare str1 str2 ix jx;
    for (ix=0 : ix<DICT_WORD_SIZE : ix++) {
        jx = (str1-->ix) - (str2-->ix);
        if (jx ~= 0) return jx;
    }
    return 0;
];

§10. Command Tables. The VM is also generated containing a data structure for the grammar produced by I6's Verb and Extend directives: this is essentially a list of command verbs such as DROP or PUSH, together with a list of synonyms, and then the grammar for the subsequent commands to be recognised by the parser. 

[ VM_CommandTableAddress i;
    return (#grammar_table)-->(i+1);
];

[ VM_PrintCommandWords i wd j dictlen entrylen;
    dictlen = #dictionary_table-->0;
    entrylen = DICT_WORD_SIZE + 7;
    for (j=0 : j<dictlen : j++) {
        wd = #dictionary_table + WORDSIZE + entrylen*j;
        if (DictionaryWordToVerbNum(wd) == i)
            print "'", (address) wd, "' ";
    }
];

§11. Action functions. This looks up the address of a function like TakeSub from the table of "action subroutines".

Strangely, Glulx's action routines table is numbered in an off-by-one way compared to the Z-machine's: hence the +1 here. 

[ VM_ActionFunction act;
    return #actions_table-->(act+1);
];

§12. Glulx-Only Printing Routines. Partly because of the smallness of the range of representable values in the Z-machine, there is little run-time type-checking that can be done: for instance a dictionary address cannot be distinguished from a function address because they are encoded differently, so that a function address (which is packed) could well coincide with that of a dictionary word (which is not). On Glulx these restrictions are somewhat lifted, so that it's possible to write a routine which can look at a value, work out what it must mean, and print it suitably. This is only possible up to a point — for instance, it can't distinguish an integer from a function address — and in I7 the use of this sort of trick is much less important because type-checking in the Inform compiler handles the problem much better. Still, we retain some Glulx-only features because they are convenient for writing external files to disc, for instance, something which the Z-machine can't do in any case.

Glulx_PrintAnything handles strings, functions (with optional arguments), objects, object properties (with optional arguments), and dictionary words. (Object property printing has been somewhat simplified from the ideal version of this function in order to avoid calling the CA__Pr veneer function.)

Glulx_PrintAnyToArray does the same, but the output is sent to a byte array in memory. The first two arguments must be the array address and length; subsequent arguments are as for Glulx_PrintAnything. The return value is the number of characters output. If the output is longer than the array length given, the extra characters are discarded, so the array does not overflow. (However, the return value is the total length of the output, including discarded characters.) The character set stored here is ZSCII, not Unicode.

Glulx_PrintAnyToArrayUni does the same again, but the output is sent to a word array in memory. The stored characters are Unicode code points.

Glulx_ChangeAnyToCString calls Glulx_PrintAnyToArray on a particular array, then amends the result to make it a C-style string — that is, a sequence of byte-sized characters which are null terminated. The character set stored here is once again ZSCII, not Unicode. 

Glulx_PrintAnything()                    <nothing printed>
Glulx_PrintAnything(0)                   <nothing printed>
Glulx_PrintAnything("string");           print (string) "string";
Glulx_PrintAnything('word')              print (address) 'word';
Glulx_PrintAnything(obj)                 print (name) obj;
Glulx_PrintAnything(obj, prop)           obj.prop();  NOTE: Using PrintOrRun
Glulx_PrintAnything(obj, prop, args...)  obj.prop(args...); NOTE: Unsupported
Glulx_PrintAnything(func)                func();
Glulx_PrintAnything(func, args...)       func(args...);

[ Glulx_PrintAnything _vararg_count obj mclass;
    if (_vararg_count == 0) return;
    @copy sp obj;
    _vararg_count--;
    if (obj == 0) return;

    if (obj->0 == $60) {
        Dictionary word. Metaclass() can't catch this case, so we do it manually
        print (address) obj;
        return;
    }

    mclass = metaclass(obj);
    switch (mclass) {
      nothing:
        return;
      String:
        print (string) obj;
        return;
      Routine:
        Call the function with all the arguments which are already
        on the stack.
        @call obj _vararg_count 0;
        return;
      Object:
        if (_vararg_count == 0) {
            print (name) obj;
        }
        else {
            Push the object back onto the stack, and call the
            veneer routine that handles obj.prop() calls.
            @copy obj sp;
            _vararg_count++;
            @call PrintOrRun _vararg_count 0;
        }
        return;
    }
];

[ Glulx_PrintAnyToArray _vararg_count arr arrlen str oldstr len;
    @copy sp arr;
    @copy sp arrlen;
    _vararg_count = _vararg_count - 2;

    oldstr = glk_stream_get_current();
    str = glk_stream_open_memory(arr, arrlen, 1, 0);
    if (str == 0) return 0;

    glk_stream_set_current(str);

    @call Glulx_PrintAnything _vararg_count 0;

    glk_stream_set_current(oldstr);
    @copy $ffffffff sp;
    @copy str sp;
    @glk $0044 2 0; stream_close
    @copy sp len;
    @copy sp 0;
    return len;
];

[ Glulx_PrintAnyToArrayUni _vararg_count arr arrlen str oldstr len;
    @copy sp arr;
    @copy sp arrlen;
    _vararg_count = _vararg_count - 2;

    oldstr = glk_stream_get_current();
    str = glk_stream_open_memory_uni(arr, arrlen, 1, 0);
    if (str == 0) return 0;

    glk_stream_set_current(str);

    @call Glulx_PrintAnything _vararg_count 0;

    glk_stream_set_current(oldstr);
    @copy $ffffffff sp;
    @copy str sp;
    @glk $0044 2 0; stream_close
    @copy sp len;
    @copy sp 0;
    return len;
];

Constant GG_ANYTOSTRING_LEN 66;
Array AnyToStrArr -> GG_ANYTOSTRING_LEN+1;

[ Glulx_ChangeAnyToCString _vararg_count ix len;
    ix = GG_ANYTOSTRING_LEN-2;
    @copy ix sp;
    ix = AnyToStrArr+1;
    @copy ix sp;
    ix = _vararg_count+2;
    @call Glulx_PrintAnyToArray ix len;
    AnyToStrArr->0 = $E0;
    if (len >= GG_ANYTOSTRING_LEN)
        len = GG_ANYTOSTRING_LEN-1;
    AnyToStrArr->(len+1) = 0;
    return AnyToStrArr;
];

§13. The Screen. Our generic screen model is that the screen is made up of windows: we tend to refer only to two of these, the main window and the status line, but others may also exist from time to time. Windows have unique ID numbers: the special window ID \(-1\) means "all windows" or "the entire screen", which usually amounts to the same thing.

Screen height and width are measured in characters, with respect to the fixed-pitch font used for the status line. The main window normally contains variable-pitch text which may even have been kerned, and character dimensions make little sense there. 

[ VM_ClearScreen window;
    if (window == WIN_ALL or WIN_MAIN) {
        glk_window_clear(gg_mainwin);
        if (gg_quotewin) {
            glk_window_close(gg_quotewin, 0);
            gg_quotewin = 0;
            Quote_Window.glk_ref = 0;
        }
    }
    if (gg_statuswin && window == WIN_ALL or WIN_STATUS) glk_window_clear(gg_statuswin);
];

[ VM_ScreenWidth  id;
    id = gg_mainwin;
    if (gg_statuswin) {
        id = gg_statuswin
    }
    glk_window_get_size(id, gg_arguments, 0);
    return gg_arguments-->0;
];

[ VM_ScreenHeight  height;
    glk_window_get_size(gg_mainwin, 0, gg_arguments);
    height = gg_arguments-->0;
    if (gg_statuswin) {
        glk_window_get_size(gg_statuswin, 0, gg_arguments);
        height = height + gg_arguments-->0;
    }
    return height;
];

§14. Window Colours. We can now change foreground and background colours in both Z-Machine and Glulx (through a widely implement extension.) Inform does not keep track of which colours have been set. 

[ VM_SetWindowColours fg bg;
    if (Cached_Glk_Gestalts-->gestalt_GarglkText_FAKE) {
        garglk_set_zcolors(fg, bg);
    }
];

[ VM_SetReverseMode val;
    if (Cached_Glk_Gestalts-->gestalt_GarglkText_FAKE) {
        garglk_set_reversevideo(val);
    }
];

§15. Main Window. The part of the screen on which commands and responses are printed, which ordinarily occupies almost all of the screen area.

VM_MainWindow() switches printing back from another window, usually the status line, to the main window. 

[ VM_MainWindow;
    glk_set_window(gg_mainwin); set_window
    statuswin_current=0;
];

§16. Status Line. Despite the name, the status line need not be a single line at the top of the screen: that's only the conventional default arrangement. It can expand to become the equivalent of an old-fashioned VT220 terminal, with menus and grids and mazes displayed lovingly in character graphics, or it can close up to invisibility.

VM_StatusLineHeight(n) sets the status line to have a height of n lines of type. (The width of the status line is always the width of the whole screen, and the position is always at the top, so the height is the only controllable aspect.) The \(n=0\) case makes the status line disappear.

VM_MoveCursorInStatusLine(line, column) switches printing to the status line, positioning the "cursor" — the position at which printing will begin — at the given character grid position \((line, column)\). Line 1 represents the top line; line 2 is underneath, and so on; columns are similarly numbered from 1 at the left. 

[ VM_StatusLineHeight hgt;
    if (gg_statuswin == 0) return;
    if (hgt == statuswin_cursize) return;
    glk_window_set_arrangement(glk_window_get_parent(gg_statuswin), winmethod_Fixed + winmethod_Above, hgt, 0);
    statuswin_cursize = hgt;
];

[ VM_MoveCursorInStatusLine line column;
    if (gg_statuswin == 0) return;
    glk_set_window(gg_statuswin);
    if (line == 0) { line = 1; column = 1; }
    glk_window_move_cursor(gg_statuswin, column-1, line-1);
    statuswin_current=1;
];

§17. Quotation Boxes. On the Z-machine, quotation boxes are produced by stretching the status line, but on Glulx they usually occupy windows of their own. If it isn't possible to create such a window, so that gg_quotewin is zero below, the quotation text just appears in the main window. 

[ Box__Routine maxwid arr ix lines lastnl parwin;
    maxwid = 0; squash compiler warning
    lines = arr-->0;

    if (gg_quotewin == 0) {
        gg_arguments-->0 = lines;
        if (ix == 0) {
            gg_quotewin =
                glk_window_open(gg_mainwin, winmethod_Fixed + winmethod_Above,
                    lines, wintype_TextBuffer, GG_QUOTEWIN_ROCK);
            Quote_Window.glk_ref = gg_quotewin;
        }
    } else {
        parwin = glk_window_get_parent(gg_quotewin);
        glk_window_set_arrangement(parwin, winmethod_Fixed + winmethod_Above, lines, 0);
    }

    lastnl = true;
    if (gg_quotewin) {
        glk_window_clear(gg_quotewin);
        glk_set_window(gg_quotewin);
        lastnl = false;
    }

    VM_Style(BLOCKQUOTE_VMSTY);
    for (ix=0 : ix<lines : ix++) {
        print (string) arr-->(ix+1);
        if (ix < lines-1 || lastnl) new_line;
    }
    VM_Style(NORMAL_VMSTY);

    if (gg_quotewin) {
        glk_set_window(gg_mainwin);
    }
];