[cc65] / doc / geos.sgml

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<article>

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<title>GEOSLib docs
<author>Maciej Witkowiak, <htmlurl url="mailto:ytm@elysium.pl" name="ytm@elysium.pl">
<date>v1.1, 26.12.1999, 16.03.2000, 19-22.03.2000, 11,29.07.2000, 03.07.2001
<abstract>
This is the documentation of cc65's GEOSLib, but information contained here may be also
useful for writting GEOS applications in general.
</abstract>

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<sect>Introduction
<p>
As we all know that the best computers in the world are c64 and c128. They have their GUI too -
excellent GEOS. GEOS seems very difficult and cryptic for many people, from programmer's point
of view. That's not true. The designers of GEOS created flexible and powerful system, which
is easy to use and program.
<p>
Coding GEOS in C? That's something new. It is possible now - with Ulrich von Bassewitz's cc65
package and my GEOSLib you are able to create GEOS applications in no-time.
<p>
GEOSLib supports a subset of standard cc65 libraries. Memory and string functions are included
but you should consider using native versions of these (e.g. <tt/FillRam/ instead of </ttmemset/)
at least in this version. <tt/dio/ - direct disk access is available, but you might have
problems with devices other than 1541, 1571 or 1581. RAM drives emulating these should work.
It is safe to use these includes: <tt/dio.h, errno.h, geos.h, joystick.h, mouse.h, stdlib.h,
string.h/
<p>
I am an assembler programmer and GEOSLib was designed in such way that cc65 could emit the best
available code (well, the best as for machine :). Many of the <tt/void foo (void)/ functions are
just raw calls to Kernal (assembled just as <tt/jsr _foo/), look in <tt/gsym.h/, where you
will find many definitions of standard GEOS locations. Access to these addresses is optimized by
cc65 to simple <tt/lda/ and <tt/sta/. Don't be afraid to use the power of C.

<sect1>Requirements
<p>
You will not need c64 or c128 for development. The only hardware requirement is a PC capable of
runing cc65. You will however need c64 or c128 emulator and GEOS image disks (.d64) to test your
programs.

The software needed:
<itemize>
    <item><em/cc65/ Excellent package containing C crosscompiler, crossassembler and linker, you
                can get it from: <htmlurl url="http://www.von-bassewitz.de/uz/cc65/"
                name="http://www.von-bassewitz.de/uz/cc65/">
    <item><em/VICE/ This is portable C64, C128 and few other Commodore computers emulator, you
                can obtain it from: <htmlurl url="http://www.cs.cmu.edu/~dsladic/vice/vice.html"
                name="http://www.cs.cmu.edu/~dsladic/vice/vice.html">
    <item><em/Star Commander/ This tool is for DOS right now. You will need it for transferring
                object files from PC to 1541. There's also one important ability of this
                tool - it automatically un-converts .cvt files into GEOS native format on
                disk image files.
</itemize>
<p>
VICE and cc65 are portable - they run on variety of platforms - DOS, Win32 and UNIX. GEOSLib only
needs cc65.
<p>
<em/Update:/ starting from v2.5.0 GEOSLib is a part of cc65 package as its GEOS support.

<sect1>Legal
<p>
I want to thank Uz for his cc65 package, Alexander Boyce for his excellent GEOS Programmer's
Reference Guide and BSW for GEOS.
<p>
GEOSLib is covered by the same license as cc65. You can find the whole text among documentation.
I would really appreciate if you would like to send me your comments, suggestions, questions,
changes, bug reports etc. I will also appreciate if you will just give me a sign that you are
using GEOSLib - not especially something big and important, mail me even if you are just playing
with it.
<p>
You can send postcards with hellos to:
<p>
Maciej Witkowiak, ul. Slowackiego 6/57, 77-400 ZLOTOW
<p>
POLAND
<p>
e-mail: <tt/ytm@elysium.pl/

<sect>What have you got and what to do with it?
<p>
This chapter describes some rules you ought to obey, and how to use GEOSLib.

<sect1>General rules
<p>
Think twice before you use standard C library function. In current implementation almost always
you will get better code using only <tt/geos.h/. This will change in next releases as standard
functions will become wrappers to native GEOS Kernal.
<p>
Apart from this file, which merely describes only standard GEOS library functions, you should read
<tt/grc/ (GEOS resource compiler) documentation. There are informations about necessary resource
files (each GEOS application neeeds at least one) and the building process - what should be done
and in which order.

<sect1>Usage
<p>
All in all, you just need to place
<tscreen><verb>
&num;include &lt;geos.h&gt
</verb></tscreen>
on top of your source.
<p>
Please read cc65's documentation on how to compile C, assembler and link everything together.
<p>
GEOSLib building process isn't yet defined stable. Detailed information how to link everything
together is in separated file together with resource compiler documentation.
<p>
As a general rule read the sources of example programs and read the headers. These are the most
reliable sources of knowledge ;). You will also find there many C macros representing various
arguments passed to functions. Please use them. You will find your sources easier to understand,
and it will be easier to find bugs.
<p>
All types used in GEOSLib are <tt/unsigned/.
<p>
Screen coordinates are given in pixels unless stated differently.

<sect1>Notes on style
<p>
All programs start their execution on <tt/main/ function. Unlike plain C exiting from this function
doesn't mean end of program. GEOS is event-driven environment where applications are only executing
events, main loop is in kernal. <tt/main/ function should setup the screen, menus etc. and return.
Real end of the program should be called from event call, e.g. from menu item. You can force end of
program and return to DeskTop either by standard <tt/exit (0)/ function or by <tt/EnterDeskTop()/.
Currently they are almost the same (last minute note: don't use <tt/exit/ ever, it's broken right
now :-).
<p>
Whenever possible use definitions from <tt/gsym.h/. The resulting code is translated by cc65 into
series of <tt/lda/ and <tt/sta/, so you can't do it better :-).
<p>
Don't hesitate to use library functions. Everything was written with size and speed in mind. In
fact many calls are just redirections to GEOS kernal which results in simple <tt/jsr/.
<p>
You might wonder why I have chosen sometimes weird order of arguments in functions. It is because
I wanted to avoid unnecessary pushing and popping arguments from stack. cc65 can pass single <tt/int/
through CPU registers.
<p>
Do not try to compile in strict ANSI mode. I'm using some cc65 extensions which are not available in
ANSI.

<sect>Library Functions
<p>
Functions here are sorted more or less in the way they appear in header files. This way I am able
to keep functions covering similar task near each other. All function names are identical to those
from <tt/geosSym/ file provided with GeoProgrammer package. Only my extensions to <tt/geosSym/
are covered by new names, but I tried to keep them in the naming convention.

<sect1>Graphics
<p>
This section covers drawing package of GEOS along with text output routines.

<sect2>SetPattern
<p>
<tt/void SetPattern (char pattern)/
<p>
This function sets current pattern to given. There are 32 different patterns in GEOS. You can
see them together in the filling box in GeoPaint.

<sect2>GraphicsString
<p>
<tt/void GraphicsString (char *myGString)/
<p>
One of the more powerfull routines of GEOS. This function calls other graphic functions depending
on given command string. See structures chapter for more detailed description of the structure of it.

<sect2>Rectangle functions
<p>
Parameters to those functions are grouped in <tt/struct window drawWindow/. To speed up things and
reduce overhead this structure is glued to zero page locations, where all rectangle functions
expect their parameters. You can modify data directly (e.g. <tt/drawWindow.top=10/) or via
<tt/InitDrawWindow/ function. Contents of <tt/drawWindow/ are guaranteed not to change only when
using graphics functions. In other case you should keep your data in separate <tt/struct window/
and use <tt/InitDrawWindow/ before first call to rectangle functions.

<sect3>InitDrawWindow
<p>
<tt/void InitDrawWindow (struct window *myWindow)/
<p>
This function only copies contents of <tt/myWindow/ into system area of <tt/drawWindow/. Use it
if for some reason you have to keep window data out of zero page space.

<sect3>Rectangle
<p>
<tt/void Rectangle (void)/
<p>
This draws on screen rectangle filled with current pattern.

<sect3>FrameRectangle
<p>
<tt/void FrameRectangle (char pattern)/
<p>
This one draws frame with given line pattern.

<sect3>InvertRectangle
<p>
<tt/void InvertRectangle (void)/
<p>
Just as the name says...

<sect3>ImprintRectangle and RecoverRectangle
<p>
<tt/void ImprintRectangle (void)/
<p>
<tt/void RecoverRectangle (void)/
<p>
These two functions are for copying parts of the screen to (<tt/Imprint/) and from (<tt/Recover/)
backbuffer of the screen. For example when drawing new menu box GEOS first uses
<tt/ImprintRectangle/ to save the area under the box, and restores it by <tt/RecoverRectangle/ upon
destroying the menu.

<sect2>Line Functions
<p>
GEOS drawing package is optimized so there are different functions for drawing vertical and
horizontal lines.

<sect3>HorizontalLine
<p>
<tt/void HorizontalLine (char pattern, char y, int xStart, int xEnd)/
<p>
This function draws horizontal line using given pattern - here it is a true bit pattern, not
pattern set by <tt/SetPattern/.

<sect3>InvertLine
<p>
<tt/void InvertLine (char y, int xStart, int xEnd)/
<p>
There is only horizontal version.

<sect3>RecoverLine
<p>
<tt/void RecoverLine (char y, int xStart, int xEnd)/
<p>
This function recovers only one line. It is utilized by <tt/RecoverRectangle/. See its description
for more details.

<sect3>VerticalLine
<p>
<tt/void VerticalLine (char pattern, char yStart, char yEnd, int x)/
<p>
This function draws vertical line using given pattern. Note that <tt/pattern/ is not a pattern
number as set in <tt/SetPattern/ but a true bit pattern.

<sect3>DrawLine
<p>
<tt/void DrawLine (struct window *myWindow)/
<p>
<tt/top/ parameters of <tt/struct window/ describe the starting point of the line, while
<tt/bottom/ are for the ending point. Current pattern is used for drawing.

<sect2>Point Functions
<p>
Parameters to these two functions are passed by a pointer to own <tt/struct pixel/ filled with
proper values.

<sect3>DrawPoint
<p>
<tt/void DrawPoint (struct pixel *myPixel)/
<p>
Draws single point on the screen, no matter what the current pattern is.

<sect3>TestPoint
<p>
<tt/char TestPoint (struct pixel *myPixel)/
<p>
This function tests if given pixel is set and returns true or false.

<sect2>Character and string output

<sect3>PutChar
<p>
<tt/void PutChar (char character, char y, char x)/
<p>
This function outputs single character using current style and font to screen.

<sect3>PutString
<p>
<tt/void PutString (char *myString, char y, int x)/
<p>
Same as <tt/PutChar/ except the fact that you can output whole <tt/NULL/-terminated string.
See <tt/ggraph.h/ for list of tokens that you can also place in the string - like <tt/CBOLDON/ or
<tt/COUTLINEON/.

<sect3>PutDecimal
<p>
<tt/void PutDecimal (char parameter, int value, char y, int x)/
<p>
This function converts <tt/value/ to its decimal representation and outputs it to the screen.
Depending on given <tt/parameter/ the string can be filled with zeroes (string always 5 characters
long) or not, to be left or right justified to given pixel. See <tt/ggraph.h/ for predefined
values for <tt/parameter/.

<sect2>Font Handling

<sect3>GetCharWidth
<p>
<tt/char GetCharWidth (char character)/
<p>
This function returns real width (in pixels) of given character with current font. It can be used
for counting the length of string on screen, allowing for indentation or justification.

<sect3>LoadCharSet
<p>
<tt/void LoadCharSet (struct fontdesc *myFont)/
<p>
This function forces GEOS to use given font instead of own. <tt/myFont/ should be casted from
pointer to the start of area where was loaded record from font file (VLIR structure).

<sect3>UseSystemFont
<p>
<tt/void UseSystemFont (void)/
<p>
This function forces GEOS to use built-in BSW font.

<sect2>Bitmap handling
<p>
I'm not quite sure how are these functions working (except <tt/BitmapUp/) so you should
probably look into library sources and compare it with your knowledge. Please let me know
if something is wrong or broken.

<sect3>BitmapUp
<p>
<tt/void BitmapUp (struct iconpic *myPic)/
<p>
This function unpacks the bitmap and places it on the screen - just as you set it in the
<tt/struct iconpic/ pointer to which you pass. See <tt/gstruct.h/ for description of this
structure. Note that you can only use packed GEOS bitmaps - simple Photo Scrap is in this format.

<sect3>BitmapClip
<p>
<tt/void BitmapClip (char skipLeft, char skipRight, int skipTop, struct iconpic *myPic)/
<p>
This function acts similar to <tt/BitmapUp/ but you can also define which parts of the bitmap are
to be drawn - you give the number of columns (8-pixel) to skip on the right and left of the bitmap,
and the number of rows to skip from the top if it.

<sect3>BitOtherClip
<p>
<tt/void BitOtherClip (void *proc1, void *proc2, char skipLeft, char skip Right, int skipTop,
        struct iconpic *myPic)/
<p>
Similar to the previous one with some extension. <tt/proc1/ is called before reading a byte (it
returns in .A next value), and <tt/proc2/ is called every time the parser reads a byte which is
not a piece of pattern (byte of code greater than 219). Both procedures should be written
separately in assembler and declared as <tt/__fastcall__/ returning char.

<sect1>Menus and Icons
<p>
Here you will find information about functions related with menus and icons.

<sect2>Menus
<p>
Menus are essencial for GUI. GEOS can handle only one menu at a time, but each menu can call
another one, which results in submenu tree. There can be up to 8 menu levels, each one with up
to 32 items.
<p>
Menus are initialized with <tt/DoMenu/ and then Kernal takes care for everything. Your code
(called from event handler) should be a function without parameters, returning void. You should
use <tt/DoPreviousMenu/ or <tt/GotoFirstMenu/ at least once in its code to have the screen clean.

<sect3>DoMenu
<p>
<tt/void DoMenu (struct menu *myMenu)/
<p>
This function initializes GEOS menu processor and exits. See <tt/DoMenu structure/ for more
information about it. Know that many GEOS application just initializes the screen, menu and
exits to main Kernal loop, this proves the power of <tt/DoMenu/.

<sect3>ReDoMenu
<p>
<tt/void ReDoMenu (void)/
<p>
This simply redraws the menu at lowest level. It works like calling <tt/DoMenu/ again with
the same parameters.

<sect3>RecoverMenu
<p>
<tt/void RecoverMenu (void)/
<p>
This function erases current menu from the screen. It doesn't change the menu level.

<sect3>RecoverAllMenus
<p>
<tt/void RecoverAllMenus (void)/
<p>
This calls <tt/RecoverMenu/ and erases all menus from the screen. Then the menu level is
set to 0 (topmost).

<sect3>DoPreviousMenu
<p>
<tt/void DoPreviousMenu (void)/
<p>
This functions causes menu processor to go back one menu level. You should use it in menu
handler code to have the screen clean.

<sect3>GotoFirstMenu
<p>
<tt/void GotoFirstMenu (void)/
<p>
This one jumps back to the topmost menu. If there is only menu and submenu it works the
same as <tt/DoPreviousMenu/.

<sect2>Icons
<p>
Icons are working similar to menus except the fact that there is only one level. Icons are
defined as a screen area filled with a bitmap, but if you would setup icons and erase the
screen they are still active and clicking in the place where formerly an icon was will cause
an effect. Similary if you would setup icons and then turn them off with <tt/ClearMouseMode/
the bitmap will be still on the screen but clicking on it would not cause any action.
There is only one, but powerful icon function.

<sect3>DoIcons
<p>
<tt/void DoIcons (struct icontab *myIconTab)/
<p>
This function initializes all icons that are present on the screen at once. For more information
look at <tt/Icons/ chapter in this manual.

<sect1>DialogBoxes
<p>
This chapter covers the most powerful GEOS user interface function - <tt/DoDlgBox/.

<sect2>GEOS standard

<sect3>DoDlgBox
<p>
<tt/char DoDlgBox (char *dialogString)/
<p>
DialogBox returns one byte. It can be the value of one of six standard icons (see <tt/gdlgbox.h/)
or whatever closing routine passes. Register <tt/r0L/ also contains this value.
<p>
Read structures chapter for the specs of the <tt/dialogString/.

<sect3>RstrFrmDialogue
<p>
<tt/char RstrFrmDialogue/
<p>
This function called from within DialogBox event immediately closes the DialogBox and returns
the owner ID (or whatever caller has in the .A register).

<sect2>GEOSLib extensions
<p>
To simplify usage of DoDlgBox from C I've wrote some help functions - wrappers for DoDlgBox,
with predefined data. In one word - these are standard DialogBoxes you can see in almost every
GEOS application.

<sect3>DlgBoxYesNo, DlgBoxOkCancel, DlgBoxOk
<p>
<tt/char DlgBoxYesNo (char *line1, char*line2)/
<p>
<tt/char DlgBoxOkCancel (char *line1, char*line2)/
<p>
<tt/void DlgBoxOk (char *line1, char*line2)/
<p>
These function show two lines of text in standard-sized DialogBox. You can read the code of
pressed icon from return value. E.g. for <tt/DlgBoxYesNo/ it can only be <tt/YES/ or <tt/NO/.

<sect3>DlgBoxGetString
<p>
<tt/char DlgBoxGetString (char *string, char strlen, char *line1, char *line2)/
<p>
This function prompts user for entering a string of at most <tt/strlen/ characters. It is returned
in <tt/string/. The two given lines of text are shown above the input line. Please remember
that there is also <tt/CANCEL/ icon in the DialogBox and you should test if user confirmed his
input or gave up. The <tt/string/ is also shown so you can place default input there or remember
to place <tt/NULL/ at start.

<sect3>DlgBoxFileSelect
<p>
<tt/char DlgBoxFileSelect (char *class, char filetype, char *filename)/
<p>
This routine is the standard file selector. It can return <tt/OPEN/, <tt/CANCEL/ or disk error
on reading the directory or opening the disk.
There is also <tt/DISK/ icon shown, but it is handled internally. You pass as input parameters
<tt/filetype/ and pointer to string containing the first part of file's class. If this string is
empty (<tt/NULL/ at the start), then all files with given filetype will be shown.
<p>
At present this file selector handles only first 16 files of given type and supports only one
(current) drive.

<sect1>Mouse, Sprites and Cursors
<p>
You will find here functions related to sprite and mouse drawing and handling.

<sect2>Mouse related functions
<p>
These cover mouse - as a general pointing device, but expect user to utilize as different devices
as digital or analog joystick, mouse, lightpen or koalapad (whatever it is).

<sect3>StartMouseMode
<p>
<tt/void StartMouseMode (void)/
<p>
This function initializes mouse vectors - <tt/mouseVector/ and <tt/mouseFaultVec/, and then
calls <tt/MouseUp/.

<sect3>ClearMouseMode
<p>
<tt/void ClearMouseMode (void)/
<p>
This function disables all mouse actitivies - icons and menus stop to respond to mouse events,
but they are not cleared from the screen.

<sect3>MouseUp and MouseOff
<p>
<tt/void MouseUp (void)/
<p>
<tt/void MouseOff (void)/
<p>
The first function turns the mouse pointer on. It will appear on next IRQ. The second one does
the opposite - it turns off the pointer, but its position is still updated by input driver.

<sect3>IsMseInRegion
<p>
<tt/char IsMseInRegion (struct window *myWindow)/
<p>
This function tests if mouse pointer is actually in given range of screen. See <tt/gsprite.h/ for
description of bits in return values - they describe the position in detail.

<sect2>Sprites
<p>
You are free to use any of the eight sprites, but keep in mind that sprite 0 is actually the mouse
pointer and sprite 1 can be overwritten when using text prompt.

<sect3>DrawSprite
<p>
<tt/void DrawSprite (char sprite, char *mySprite)/
<p>
This function initializes the sprite data. <tt/mySprite/ is a 63-byte table with bitmap data, which
is copied to system sprite area (at <tt/sprpic/ - see <tt/gsym.h/). Hardware sprite registers are
not initialized and sprite is not yet visible.

<sect3>PosSprite
<p>
<tt/void PosSprite (char sprite, struct pixel *myPixel)/
<p>
This function positions the sprite on the screen. Given coordinates are screen ones - they are
converted to sprite coordinates by GEOS. Due to this you cannot use this function to position your
sprite off the left or top to the screen.

<sect3>EnablSprite and DisablSprite
<p>
<tt/void EnablSprite (char sprite)/
<p>
<tt/void DisablSprite (char sprite)/
<p>
These two functions are responsible for making the sprite visible or not.

<sect2>Cursors and Console

<sect3>InitTextPrompt
<p>
<tt/void InitTextPrompt (char height)/
<p>
This function initializes sprite 1 for text prompt with given <tt/height/. This parameter can be in
range 1-48.

<sect3>PromptOn and PromptOff
<p>
<tt/void PromptOn (struct pixel *myPixel)/
<p>
<tt/void PromptOff (void)/
<p>
The first function places text prompt in given place and enables its blinking
The second one is pretty self-explanatory.

<sect3>GetNextChar
<p>
<tt/char GetNextChar (void)/
<p>
This function gets next character from the keyboard queue. If the queue is empty it returns
<tt/NULL/, otherwise you receive true ASCII code of a character or value of special (function)
key. See <tt/gsprite.h/ for list of them.

<sect1>Disk
<p>
This chapter covers slightly low-level disk routines. You should use them with care, because
you may easily corrupt data on disks. Also remember that contemporary GEOS supports many various
devices and sticking to 1541 track layout (e.g. expecting the directory on track 18) might be
dangerous.
<p>
For some purposes you might consider using <tt/dio.h/ interface to disk access. It is native.
<p>
All GEOS disk functions return error code in X register. In some cases this is returned by
GEOSLib function (if its type is <tt/char/), but in all cases last error is saved in <tt/errno/
location. If it is nonzero - an error occured. See <tt/gdisk.h/ for list of errorcodes.
<p>
Passing parameters use always e.g. <tt/ReadBuff (&amp;myTrSe)/.

<sect2>Buffer functions
<p>
These functions are taking single data sector (256 bytes) to read or write on a disk.

<sect3>ReadBuff and Writebuff
<p>
<tt/char ReadBuff (struct tr_se *myTrSe)/
<p>
<tt/char WriteBuff (struct tr_se *myTrSe)/
<p>
These functions are reading and writting sector placed at <tt/diskBlkBuf/.

<sect3>GetBlock and ReadBlock
<p>
<tt/char GetBlock (struct tr_se *myTrSe, char *buffer)/
<p>
<tt/char ReadBlock (struct tr_se *myTrSe, char *buffer)/
<p>
These two functions are reading a single block directly at 256 byte array placed at <tt/buffer/.
The difference between them is that <tt/GetBlock/ will initialize TurboDos in drive if it was not
enabled. <tt/ReadBlock/ assumes that it is already enabled thus being slightly faster.

<sect3>PutBlock, WriteBlock, VerWriteBlock
<p>
<tt/char PutBlock (struct tr_se *myTrSe, char *buffer)/
<p>
<tt/char WriteBlock (struct tr_se *myTrSe, char *buffer)/
<p>
<tt/char VerWriteBlock (struct tr_se *myTrSe, char *buffer)/
<p>
Similar to previous but needed for writting the disk. <tt/VerWriteBlock/ verifies the data after
writting. In case of error five tries are attempted before error code is returned.

<sect2>Directory header
<p>
Functions described here are operating on <tt/curDirHeader/ where current disk header is stored.
On larger capacity drives (than 1541) the second part of directory header in <tt/dir2Head/.

<sect3>GetPtrCurDkNm
<p>
<tt/void GetPtrCurDkNm (char *diskName)/
<p>
This function fills given character string with the name of current disk. It is converted to C
standard - string is terminated with <tt/NULL/ character instead of code 160 as in Commodore DOS.
Note that passed pointer must point to an array of at least 17 bytes.

<sect3>GetDirHead and PutDirHead
<p>
<tt/char GetDirHead (void)/
<p>
<tt/char PutDirHead (void)/
<p>
These functions are reading and writting the directory header. You should use <tt/GetDirHead/ before
using any functions described below, and you should use <tt/PutDirHead/ to save the changes on the
disk. Otherwise they will be lost. Operating area is the <tt/curDirHead/.

<sect3>CalcBlksFree
<p>
<tt/int CalcBlksFree (void)/
<p>
This function returns the number of free blocks on current disk. It is counted using data in
<tt/curDirHead/ so you must initialize the disk before calling it.

<sect3>ChkDskGEOS
<p>
<tt/char ChkDskGEOS (void)/
<p>
This functions checks <tt/curDirHead/ for GEOS Format identifier. It returns either true or false,
and also sets <tt/isGEOS/ properly. You must initialize the disk before using this.

<sect3>SetGEOSDisk
<p>
<tt/char SetGEOSDisk (void)/
<p>
This function initializes disk for use with GEOS. It sets indicator in directory header and
allocates a sector for the directory of border files. You don't need to initialize the disk before
using.

<sect3>FindBAMBit
<p>
<tt/char FindBAMBit (struct tr_se *myTrSe)/
<p>
This function returns the bit value from BAM (Block Allocation Map) for given sector. The bit is
set if the sector is free to use. Returned value is always zero if the sector is already allocated.
In fact, this function could be used in a following way:
<tscreen><verb>
&num;define BlockInUse FindBAMBit
...
if (!SectInUse(&amp;myTrSe)) &lcub;
... block not allocated ...
&rcub;
</verb></tscreen>
<p>
Anyway, I feel that this function is too low-level.

<sect3>BlkAlloc and NxtBlkAlloc
<p>
<tt/char BlkAlloc (struct tr_se output&lsqb;&rsqb, int length)/
<p>
<tt/char NxtBlkAlloc (struct tr_se *myTrSe, struct tr_se output&lsqb;&rsqb, int length)/
<p>
Both functions are allocating enough disk sectors to fit the number of <tt/length/ in them. You
will find output in <tt/output/ which is table of <tt/struct tr_se/. The last entry will have the
number of track equal to 0 and sector equal to 255. The simpliest way of using them is to use
predefined space in GEOS data space and pass <tt/fileTrScTab/, which is a predefined table.
<p>
The difference between those two is that <tt/NextBlkAlloc/ will start allocating from given sector,
and <tt/BlkAlloc/ starts from the first nonused sector.
<p>
You need to use <tt/PutDirHead/ later to save any changes in BAM.

<sect3>FreeBlock
<p>
<tt/char FreeBlock (struct tr_se *myTrSe)/
<p>
Simply deallocates a block in BAM. You need to update BAM with <tt/PutDirHead/.

<sect3>SetNextFree
<p>
<tt/struct tr_se SetNextFree (struct tr_se *myTrSe)/
<p>
This function finds the first free sector starting from given track and sector and allocates it.
It might return the same argument if the given block is not allocated. I wanted it to be type
clean, but it made usage a bit tricky. To assign a value to own <tt/struct tr_se/ you have to
cast both variables to <tt/int/. E.g.
<tscreen><verb>
struct tr_se myTrSe;
...
(int)myTrSe=(int)SetNextFree(&amp;otherTrSe);
</verb></tscreen>
<p>
In this example <tt/otherTrSe/ can be replaced by <tt/myTrSe/.
<p>
NOTE that you <em/must/ use casting to have correct values.

<sect2>Low-level disk IO
<p>
Functions described here are more usable in kernal or drivers code, less common in applications,
but who knows, maybe someone will need them.

<sect3>EnterTurbo, ExitTurbo, PurgeTurbo
<p>
<tt/void EnterTurbo (void)/
<p>
<tt/void ExitTurbo (void)/
<p>
<tt/void PurgeTurbo (void)/
<p>
These functions are interface to GEOS TurboDos feature which makes slow Commodore drives a bit
more usable. <tt/EnterTurbo/ enables TurboDos unless it is already enabled. If not, then you will
have to wait a bit to transfer TurboDos code into disk drive RAM. <tt/ExitTurbo/ disables TurboDos.
This is useful for sending some DOS commands for drive e.g. for formatting. Note that before any
interaction with Kernal in ROM you have to call <tt/InitForIO/. You don't have to worry about speed.
<tt/EnterTurbo/ will only enable TurboDos (no code transfer) if TurboDos was disabled with
<tt/ExitTurbo/. <tt/PurgeTurbo/ acts different from <tt/ExitTurbo/ - it not only disables TurboDos,
but also removes it from drive RAM (not quite true, but it works like that). After using
<tt/PurgeTurbo/ the next call to <tt/EnterTurbo/ will reload drive RAM.

<sect3>ChangeDiskDevice
<p>
<tt/char ChangeDiskDevice (char newDevice)/
<p>
This function changes logical number of current device (in fact drives only) with given one. It is
usable for swapping drives. There's no check if given <tt/newDevice/ already exist, so if you want
to change the logical number of drive 8 to 9 and you have drive number 9 then GEOS will probably
hang on disk access. Use safe, large numbers. Note that safe IEC range is 8-31.

<sect2>Disk Initialization
<p>
GEOS has two functions for initialization ('logging' as they say on CP&bsol;M) the disk.
<sect3>OpenDisk
<p>
<tt/char OpenDisk (void)/
<p>
This function initializes everything for a new disk. It loads and enables TurboDos if needed.
Then the disk is initialized with <tt/NewDisk/. Next, <tt/GetDirHead/ initializes <tt/curDirHead/.
Disk names are compared and if they differ then disk cache on REU is cleared. Finally format is
checked with <tt/ChkDkGEOS/ and disk name is updated in internal tables.

<sect3>NewDisk
<p>
<tt/char NewDisk (void)/
<p>
This function is similar to DOS command I. It clears REU cache and enables TurboDos if needed.

<sect1>Files
<p>
This section cover GEOS file interface.

<sect2>Directory handling
<p>
Functions described here are common for SEQ and VLIR structures.

<sect3>Get1stDirEntry and GetNxtDirEntry
<p>
<tt/struct filehandle *Get1stDirEntry (void)/
<p>
<tt/struct filehandle *GetNxtDirEntry (void)/
<p>
These two functions are best suited for scanning whole directory for particular files. Note that
returned filehandles describes all file slots in the directory - even those with deleted files.
The return value can be obtained by casting both sides to <tt/int/ - as in <tt/SetNextFree/
function or read directly after call to those two functions from <tt/r5/. Current sector number
is in <tt/r1/ and sector data itself is in <tt/diskBlkBuf/.

<sect3>FindFile
<p>
<tt/char FindFile (char *fName)/
<p>
This function scans whole directory for the given filename. It returns either 0 (success) or 5
(FILE_NOT_FOUND, defined in <tt/gdisk.h/) or any other fatal disk read error. After successful
<tt/FindFile/ you will have <tt/struct filehandle/ at <tt/dirEntryBuf/ filled with file's data and
other registers set as described in <tt/GetNxtDirEntry/.

<sect3>FindFTypes
<p>
<tt/char FindFTypes (char *buffer, char fType, char fMaxNum, char *classTxt)/
<p>
This function scans directory and fills a table at <tt/buffer/ with <tt/char &lsqb;17&rsqb;/ entries.
<tt/fType/ is GEOS type of searched files and <tt/classTxt/ is a string for Class field in file
header. Class will match if given will be equal or shorter than that found in file's header block.
If you want just to find all files with given GEOS type you should pass empty string or <tt/NULL/ as
<tt/classTxt/. Be warned that for searching <tt/NON_GEOS/ files must pass <tt/NULL/ as <tt/classTxt/.
<tt/fMaxNum/ is the maximal number of found files, thus the <tt/buffer/ must
provide area of size equal to <tt/17 * fMaxNum/.
This function returns the number of found files, ranging from 0 to number passed as <tt/fMaxNum/.
Return value can be also restored from <tt/r7H/.

<sect3>DeleteFile
<p>
<tt/char DeleteFile (char *fName)/
<p>
This function deletes a file by its name. It works for SEQ and VLIR files.

<sect3>RenameFile
<p>
<tt/char RenameFile (char *oldName, char *newName)/
<p>
I think it is obvious...

<sect3>GetFHdrInfo
<p>
<tt/char GetFHdrInfo (struct filehandle *myFile)/
<p>
This function loads the file header into <tt/fileHeader/ buffer. Using after e.g. <tt/FindFile/
you can pass address of <tt/dirEntryBuf/.

<sect2>Common and SEQ structure
<p>
Functions described here are common for SEQ and VLIR structures because arguments passed are
starting track and sector which may point either to start of a chain for VLIR or data for SEQ.

<sect3>ReadFile
<p>
<tt/char ReadFile (struct tr_se *myTrSe, char *buffer, int fLength)/
<p>
This function reads at most <tt/fLength/ bytes into <tt/buffer/ from chained sectors starting at
<tt/myTrSe/.

<sect3>ReadByte
<p>
<tt/char ReadByte (void)/
<p>
This function returns next byte from a file. Before the first call to it you must load <tt/r5/
with <tt/NULL/, <tt/r4/ with sector buffer address and <tt/r1/ with track and sector of the
first block of a file.
Remember to not modify <tt/r1/, <tt/r4/ and <tt/r5/. These registers must be preserved between
calls to <tt/ReadByte/.
<p>
Returned value is valid only if there was no error. End of file is marked as <tt/BFR_OVERFLOW/
in <tt/errno/, this is set when trying to read one byte after the end of file, in this case
returned value is invalid.

<sect3>SaveFile
<p>
<tt/char SaveFile (struct fileheader *myHeader)/
<p>
<tt/SaveFile/ will take care of everything needed to create a GEOS file, no matter VLIR of SEQ
structure. All you need to do is to place data in proper place and prepare a header which will
contain all information about a file.

You have to declare a <tt/struct fileheader/ and fill it with proper values. There is only one
difference - the first two bytes which are link to nonexistant next sector are replaced by a
pointer to the DOS filename of the file.

When saving files two most important fields in <tt/struct fileheader/ are <tt/fileheader.load_address/
and <tt/fileheader.end_address/.

<sect3>FreeFile
<p>
<tt/char FreeFile (struct tr_se myTable&lsqb;&rsqb;)/
<p>
This function deallocates all sectors contained in passed table.

<sect3>FollowChain
<p>
<tt/char FollowChain(struct tr_se *myTrSe, char *buffer)/
<p>
This function fills a <tt/struct tr_se/ table at <tt/buffer/ with sector numbers for chain of
sectors starting with <tt/myTrSe/. You can pass such data (<tt/buffer/) to e.g. <tt/FreeFile/.

<sect2>VLIR structure
<p>
Here are informations about VLIR files (called later as RecordFile) and functions.
<p>
VLIR is a file which consists of up to 127 SEQ-like files called records. Each record is like one
SEQ structure file. Records are grouped together, described by common name - VLIR file name and
own number. Each record pointed by its number is described by starting track and sector numbers.
VLIR structures allow records to be empty (<tt/tr_se/ of such record is equal to <tt/&lcub;NULL,$ff&rcub;/),
or even non-exist (<tt/&lcub;NULL,NULL&rcub;/). Any other numbers represent starting track and sector of
particular file.
<p>
In GEOS there can be only one file opened at a time. Upon opening VLIR file some information
about it are copied into memory. You can retrieve records table at <tt/fileTrScTab/ (table of
128 <tt/struct tr_se/) and from <tt/VLIRInfo/ (<tt/struct VLIR_info/.
E.g. size of whole VLIR file can be retrieved by reading <tt/VLIRInfo.fileSize/.

<sect3>OpenRecordFile
<p>
<tt/char OpenRecordFile (char *fName)/
<p>
This function finds and opens given file. An error is returned if file is not found or it is not
in VLIR format. Information in <tt/VLIRInfo/ is initialized. VLIR track and sector table is
loaded at <tt/fileTrScTab/ and will be valid until call to <tt/CloseRecordFile/ so don't modify it.
You should <tt/PointRecord/ before trying to do something with file.

<sect3>CloseRecordFile
<p>
<tt/char CloseRecordFile (void)/
<p>
This function calls <tt/UpdateRecordFile/ and clears internal GEOS variables.

<sect3>UpdateRecordFile
<p>
<tt/char UpdateRecordFile (void)/
<p>
This function fill check <tt/VLIRInfo.fileWritten/ flag and if it is set, then <tt/curDirHead/ will
be updated along with size and date stamps in directory entry.

<sect3>PointRecord
<p>
<tt/char PointRecord (char recordNumber)/
<p>
This function will setup internal variables (and <tt/VLIRInfo.curRecord/) and return the track and
sector of given record in <tt/r1/. Note that the data may not be valid (if record is non-existing
you will get 0,0 and if it is empty - 255, 0).

<sect3>NextRecord and PreviousRecord
<p>
<tt/char NextRecord (void)/
<p>
<tt/char PreviousRecord (void)/
<p>
These two work like <tt/PointRecord/. Names are self-explanatory.

<sect3>AppendRecord
<p>
<tt/char AppendRecord (void)/
<p>
This function will append an empty record ( pair of 255,0 ) to current VLIR track and sector
table. It will also set <tt/VLIRInfo.curRecord/ to its number.

<sect3>DeleteRecord
<p>
<tt/char DeleteRecord (void)/
<p>
This function will remove current record from the table, and move all current+1 records one place
back (in the table). Note that there's no BAM update and you must call <tt/UpdateRecordFile/ to
commit changes.

<sect3>InsertRecord
<p>
<tt/char InsertRecord (void)/
<p>
This function will insert an empty record in place of <tt/VLIRInfo.curRecord/ and move all following
records in table one place forward (contents of <tt/VLIRInfo.curRecord/ after call to <tt/InsertRecord/
can be found in <tt/VLIRInfo.curRecord + 1/).

<sect3>ReadRecord and WriteRecord
<p>
<tt/char ReadRecord (char *buffer, int fLength)/
<p>
<tt/char WriteRecord (char *buffer, int fLength)/
<p>
This function will load or save at most <tt/fLength/ bytes from currently pointed record into or from
<tt/buffer/.

<sect1>Memory and Strings
<p>
Functions covered in this section are common for whole C world - copying memory parts and
strings is one of the main computer tasks. GEOS also has interface to do this. These functions
are replacement for those like <tt/memset, memcpy, strcpy/ etc. from standard libraries.

However they have slighty different calling convention (order of arguments to be specific), so
please check their syntax here before direct replacing.

Please note that the memory described as <em/strings/ are up to 255 characters (without
counting the terminating <tt/NULL/), and <em/regions/ cover whole 64K of memory.

<sect2>CopyString
<p>
<tt/void CopyString (char *dest, char *src)/
<p>
This function copies string from <tt/src/ to <tt/dest/, until it reaches <tt/NULL/. <tt/NULL/
is also copied.

<sect2>CmpString
<p>
<tt/char CmpString (char *s1, char *s2)/
<p>
This function compares string <tt/s1/ to <tt/s2/ for equality - this is case sensitive, and both
strings have to have the same length. It returns either <tt/true/ or <tt/false/.

<sect2>CopyFString and CmpFString
<p>
<tt/void CopyFString (char length, char *dest, char *src)/
<p>
<tt/char CmpFString (char length, char *s1, char *s2)/
<p>
These two are similar to <tt/CopyString/ and <tt/CmpString/ except the fact, that you provide
the length of copied or compared strings. The strings can also contain several <tt/NULL/
characters - they are not treated as delimiters.

<sect2>CRC
<p>
<tt/int CRC (char *src, int length)/
<p>
This function calculates the CRC checksum for given memory range. I don't know if it is
compatible with standard CRC routines.

<sect2>FillRam and ClearRam
<p>
<tt/void FillRam (char value, char *dest, int length)/
<p>
<tt/void ClearRam (char *dest, int length)/
<p>
Both functions are filling given memory range. <tt/ClearRam/ fills with <tt/NULLs/, while
<tt/FillRam/ uses given <tt/value/. Be warned that these functions destroy <tt/r0, r1 and
r2L/ registers.

<sect2>MoveData
<p>
<tt/void MoveData (char *src, char *dest, int length)/
<p>
This functions copies one memory region to another. There are checks for overlap and the
non-destructive method is chosen. Be warned that this function destroys contents of
<tt/r0, r1 and r2/ registers.

<sect2>InitRam
<p>
<tt/void InitRam (char *table)/
<p>
This function allows to initialize multiple memory locations with single bytes or strings.
This is done with <tt/table/ where everything is defined. See structures chapter for description of
<tt/InitRam's/ command string.

<sect2>Stash, Fetch, Swap, and VerifyRAM
<p>
<tt/void StashRAM (char bank, int length, char *reuAddy, char *cpuAddy)/
<p>
<tt/void FetchRAM (char bank, int length, char *reuAddy, char *cpuAddy)/
<p>
<tt/void SwapRAM (char bank, int length, char *reuAddy, char *cpuAddy)/
<p>
<tt/ char VerifyRAM (char bank, int length, char *reuAddy, char *cpuAddy)/
<p>
These functions are interface to REU - Ram Expansion Unit. I think that they are self-explanatory.

<sect1>Processes and Multitasking
<p>
Weird? Not at all. GEOS has limited multitasking ability. You can set up a chain of functions
called in specified intervals and you can put the main program to sleep without disturbing other
tasks and making user interface unresponsive.

<sect2>InitProcesses
<p>
<tt/void InitProcesses (char number, struct process *processTab)/
<p>
This is the main initialization routine. After calling it processes are set up, but not
enabled. The parameters for <tt/InitProcesses/ are:
<itemize>
    <item><tt/number/ - number of processes
    <item><tt/processTab/ - table of <tt/struct process/, with size equal to <tt/number/
</itemize>
<p>
Single task is described by entry in <tt/processTab/, it contains two values - <tt/pointer/ to
task function and number of <tt/jiffies/ which describe the delay between calls to task. On PAL
systems there are 50 jiffies per second, while on NTSC there are 60.
<p>
The maximum number of tasks is 20. Be warned that GEOS doesn't check if parameters are valid and
if <tt/processTab/ would be too large it would overwrite existing data in GEOS space.
<p>
There's one important thing - the last entry in <tt/processTab/ has to be <tt/NULL,NULL/, so the
maximum size of <tt/processTab/ is equal to 21.
<p>
See description of <tt/process/ structure for more detailed discussion on this.

<sect2>RestartProcess and EnableProcess
<p>
<tt/void RestartProcess (char processNumber)/
<p>
<tt/void EnableProcess (char processNumber)/
<p>
These two functions start the task counter. <tt/RestartProcess/ for each process should be called
after <tt/InitProcesses/, because it resets all flags and counters and it starts the counters.
<p>
<tt/RestartProcess/ enables counters and sets their initial value to that given in <tt/processTab/.
<p>
<tt/EnableProcess/ forces given process to execute by simulating the timer running out of time.

<sect2>BlockProcess and UnBlockProcess
<p>
<tt/void BlockProcess (char processNumber)/
<p>
<tt/void UnBlockProcess (char processNumber)/
<p>
<tt/BlockProcess/ disables the execution of given process, but this does not disable the timers.
<p>
<tt/UnBlockProcess/ does the opposite.

<sect2>FreezeProcess and UnFreezeProcess
<p>
<tt/void FreezeProcess (char processNumber)/
<p>
<tt/void UnFreezeProcess (char processNumber)/
<p>
<tt/FreezeProcess/ disables timer for given process. <tt/UnFreezeProcess/ does the opposite.
This is not equal to <tt/RestartProcess/ as timers are not filled with initial value.

<sect2>Sleep
<p>
<tt/void Sleep (int jiffies)/
<p>
This function is multitasking sleep - the program is halted, but it doesn't block other functions.
The only argument here is the number of jiffies to wait until app will wake up.
<p>
You can force to sleep not only the main application routine, but also processes-tasks. Be warned
that the maximum number of sleeping functions is 20. If it would be larger it will overwrite
parameters of already sleeping functions in GEOS kernal data space, leading to crash.

<sect1>System

<sect2>FirstInit
<p>
<tt/void FirstInit (void)/
<p>
This function initializes some GEOS variables and mouse parameters. This is called on GEOS boot
up. You shouldn't use this unless you know what you are doing.

<sect2>InitForIO and DoneWithIO
<p>
<tt/void InitForIO (void)/
<p>
<tt/void DoneWithIO (void)/
<p>
These functions are called by some disk routines. You should call them only if you want to
do something with IO registers or call one of Kernal's routines.

<sect2>MainLoop
<p>
<tt/void MainLoop (void)/
<p>
Your programs exits to MainLoop upon exiting from <tt/main/, but you might need this function in
menu and icon code. When in <tt/MainLoop/ systems waits for your action - using icons, keyboard
or menus to force some specific action from program.

<sect2>EnterDeskTop
<p>
<tt/void EnterDeskTop (void)/
<p>
This is default exit code of your application. It is finish of <tt/exit()/, but you may need it
in other places of application.

<sect2>ToBASIC
<p>
<tt/void ToBASIC (void)/
<p>
This one is another way of finishing application - forcing GEOS to shutdown and exit to BASIC.
I was considering whether to include it or not, but maybe someone will need it. Which is I doubt.

<sect2>Panic
<p>
<tt/void Panic (void)/
<p>
This calls system's <tt/Panic/ handler - it shows dialog box with message
<tscreen><verb>
System error at:xxxx
</verb></tscreen>
where <tt/xxxx/ is last known execution address (caller). By default this is binded to <tt/BRK/
instruction, but it might be usable in debugging as kind of <tt/assert/.
<p>
System is halted after call to <tt/Panic/.

<sect2>CallRoutine
<p>
<tt/void CallRoutine (void &ast;myFunct)/
<p>
This is system caller routine. You need to provide pointer to a function and it will be immediately
called, unless the pointer is equal to <tt/NULL/. This is the main functionality of this function -
you need not to worry if the pointer is valid.

<sect2>GetSerialNumber
<p>
<tt/int GetSerialNumber (void)/
<p>
This function returns the serial number of system. It might be used for copy-protection, but you
shouldn't do this. Please remember that the Free Software is a true power.

<sect2>GetRandom
<p>
<tt/char GetRandom (void)/
<p>
This function returns a random number. It can be also read from <tt/random/ e.g.
<tscreen><verb>
a=random;
</verb></tscreen>
but by calling this function you are sure that the results will be always different.
<tt/random/ is updated once a frame (50Hz PAL) and on every call to <tt/GetRandom/

<sect2>SetDevice
<p>
<tt/void SetDevice (char device)/
<p>
This function sets current device to given. It might be used together with <tt/InitForIO/,
<tt/DoneWithIO/ and some Kernal routines. Unless new device is a disk drive this only sets
new value in <tt/curDevice/, in other case new disk driver is loaded from REU or internal RAM.

<sect>Library Structures
<p>
To simplify usage and optimize passing parameters to functions I have declared several structures
which describe most common objects. Some of these structures are binded to static addresses in
GEOS data space ($8000-$8fff), so you can use their fields directly in optimized way.
Please see <tt/gsym.h/ and find them. All structures are defined in <tt/gstruct.h/ and you may
find also some comments there.

<sect1>Graphics

<sect2>pixel
<p>
One simple structure describing a point on the screen.

<sect2>fontdesc
<p>
This structure describes a font in one pointsize. There is current font - <tt/struct fontdesc/
binded at <tt/curFontDesc/. You can also force GEOS to use your own fonts by calling
<tt/LoadCharSet/. You just need to open a VLIR font file and load one record - one pointsize
somewhere. At the start of this area you already have all data for <tt/fontdesc/ so you can
pass a pointer to the load adress of that pointsize to <tt/LoadCharSet/.

<sect2>window
<p>
This widely used structure holds description of a region of the screen. It describes top-left and
bottom-right corners of a window.

<sect2>iconpic
<p>
Maybe the name isn't the best - it has nothing with <tt/DoIcons/ but with bitmap functions -
<tt/BitmapUp/ for example. This structure holds parameters needed to properly decode and show
a bitmap on the screen. Bitmap has to be encoded - if you have some non-GEOS bitmaps simply
convert them to Photo Scraps - this is the format used by all GEOS bitmap functions - <tt/DoIcons/
too.

<sect1>Icons
<p>
These structures describe click boxes (icons) that can be placed on screen or in a dialog box.

<sect2>icondef
<p>
This is the definition of a single click box. Please see <tt/gstruct.h/ for description of its fields.

<sect2>icontab
<p>
This is toplevel description of icons to be placed and enabled on the screen. This structure
has following fields:
<itemize>
    <item><tt/char number/ - total number of icons declared here
    <item><tt/struct pixel mousepos/ - after finishing <tt/DoIcons/ mouse pointer will be placed in
        this point allowing you to have hint for user what is default action
    <item><tt/struct icondef tab&lsqb;&rsqb/ - this table of size equal to <tt/icontab.number/ contains
        descriptions for all icons
</itemize>

<sect1>File and Disk

<sect2>tr_se
<p>
This simple structure holds track and sector number of something. Do not expect the track to be
in range 1-35, as GEOS can support many various and weird devices. For example my C128 256K
expansion is utilized as RAMDisk with layout of 4 tracks 128 sectors each. However assuming that
track number equal to 0 is illegal might be wise.

<sect2>f_date
<p>
This is placeholder for file datestamp. This structure is also present in <tt/struct filehandle/.
GEOS is not Y2K compliant, so if current file has in <tt/filehandle.date.year/ value less than 86
you can safely assume that it is e.g. 2004 and not 1904.

<sect2>filehandle
<p>
This is main file descriptor. It is either entry in the directory (returned from file functions)
or its copy in <tt/dirEntryBuf/. This is optimized so you can safely get to the file's year e.g.
by testing <tt/dirEntryBuf.date.year/ - it will be compiled to simple <tt/LDA, STA/.

<sect2>fileheader
<p>
This structure holds fileheader description. You can load file's header into <tt/fileHeader/
fixed area using <tt/GetFHdrInfo/. (note that <tt/fileHeader/ is a place in memory while
<tt/fileheader/ is a structure).
You will also need own fileheader for <tt/SaveFile/.

<sect1>System

<sect2>s_date
<p>
This structure is defined only for <tt/system_date/. It is slightly different from <tt/f_date/
so I prepared this one. You can e.g. get or set current time using <tt/system_date.s_hour/ and
<tt/system_date.s_minute/. Accesses to these will be optimized to simple <tt/LDA/ and <tt/STA/
pair.

<sect2>process
<p>
You should declare a table of that type to prepare data for <tt/InitProcesses/. The maximum number
of processes is 20, and the last entry has to be equal to <tt/&lcub;NULL,NULL&rcub;/, so this table may hold
only 21 entries. The first member of this structure (<tt/pointer/) holds the pointer to called
function (void returning void), you will probably have to cast that pointer into int. The second
field <tt/jiffies/ holds the amount of time between calls to that function. On PAL systems there
are 50 jiffies per second, while NTSC have 60 of them.

<sect1>Few thing in detail...
<p>
GEOSLib uses cc65 non-ANSI extensions to easily initialize data in memory. This is done with a
kind of array of unspecified length and unspecified type. Here is how it goes:
<tscreen><verb>
void example = &lcub;
    (char)3, (unsigned)3, (char)0 &rcub;;
</verb></tscreen>
Which will be compiled to following string of bytes:
<tscreen><verb>
_example:
        .byte 3
        .word 3
        .byte 0
</verb></tscreen>
As you see this way it is possible to define data of any type in any order. You must remember to
cast each member to proper type.

<sect2>DoMenu structure
<p>
<tt/DoMenu/ is responsible for everything concerned with menu processing. Many, many GEOS programs
are just initializing screen and menu and exit to <tt/MainLoop/. In GEOSLib it is the same as
returning from <tt/main/ function without using <tt/exit(0)/.
<p>
Menu is described by two types of data - menu descriptors and menu items. Descriptor contains
information about following menu items, and items are containing names of entries and either
pointers to functions to execute or, in case of nested menus, pointers to submenu descriptors.
Note that submenu descriptor can be top-level descriptor, there's no difference in structure,
just in the content.
<p>
Here is how single descriptor looks like:
<tscreen><verb>
void myMenu = &lcub;
        (char)top, (char)botom,                 // this is the size of the menubox
        (unsigned)left, (unsigned)right,        // counting all items in current descriptor
        (char)number_of_items | type_of_menu,   // number of following items ORed with
                                                // type of this menu, it can be either
        // HORIZONTAL or VERTICAL if you will have also bit 6 set then menu won't be closed
        // after moving mouse pointer outside the menubox. You can have at most 31 items.
</verb></tscreen>
This is followed by <tt/number_of_items/ of following item description.
<tscreen><verb>
        ...
        "menuitemname", (char)item_type, (unsigned)pointer,
        "nextitemname", (char)item_type, (unsigned)pointer,
        ...
        "lastitemname", (char)item_type, (unsigned)pointer &rcub;;
        // Note that there isn't ending <tt/NULL/ or something like that.
</verb></tscreen>
<tt/pointer/ is a pointer to something, what it points for depends from <tt/item_type/. This one
can have following values:
<p>
<tt/MENU_ACTION/ - a function pointed by <tt/pointer/ will be called after clicking on menu item
<p>
<tt/SUB_MENU/ - <tt/pointer/ points to next menu descriptor - a submenu
<p>
Both of them can be ORed with <tt/DYN_SUB_MENU/ and then the <tt/pointer/ points to a function
which will return in <tt/r0/ needed pointer (to function to execute or a submenu).
<p>
For creating nested menus (you can have at most 8 levels of submenus) you need to declare such
structure for each submenu and top level menu.

<sect2>DoDlgBox command string
<p>
<tt/DoDlgBox/ is together with <tt/DoMenu/ one of the most powerful routines in GEOS. It is
responsible for creating dialog boxes, that is windows which task is to interact with user.
Format of the command string is following:
<tscreen><verb>
    (window size and position)
    (commands and parameters)
    NULL
</verb></tscreen>
There is custom type defined for the command string: <tt/dlgBoxStr/.

<sect3>Size and position
<p>
The first element can be specified in two ways - by using default size and position or specifying
own. The first case results in
<tscreen><verb>
const dlgBoxStr example = &lcub;
        DB_DEFPOS (pattern_of_shadow),
        ...             // commands
        DB_END &rcub;;
</verb></tscreen>
And the own size and position would be:
<tscreen><verb>
const dlgBoxStr example = &lcub;
        DB_SETPOS (pattern, top, bottom, left, right)
        ...             // commands
        DB_END &rcub;;
</verb></tscreen>

<sect3>Commands
<p>
The next element of <tt/DoDlgBox/ command string are commands themselves. First six commands are
default icons and the number of selected icon will be returned from window processor. The icons are
<tt/OK, CANCEL, YES, NO, OPEN/, and <tt/DISK/. You can use predefined macros for use them, e.g.:
<tscreen><verb>
        ...
        DB_ICON(OK, DBI_X_0, DBI_Y_0),
        ...
</verb></tscreen>
Note that the position is counted from top left corner of window, not entire screen and that the 'x'
position is counted in cards (8-pixel) and not in pixels. This is true also for all following commands.
<tt/DBI_X_0/ and <tt/DBI_Y_0/ are predefined (see <tt/gdlgbox.h/ for more), default positions
which will make icons to appear on default window exactly where you would expect them.
<p>
<tt/DB_TXTSTR (x, y, text)/ will cause to show given text in the window.
<p>
<tt/DB_VARSTR (x, y, ptr)/ works as above, but here you are passing a pointer to a zero page location
where the address of text is stored. This is useful for information windows where only text content
is variable. Consider following:
<tscreen><verb>
char text = "foo";
        ...
        r15=(int)text;          // in code just before call to DoDlgBox
        ...
        DB_VARSTR (TXT_LN_X, TXT_LN_1_Y, &amp;r15),
        ...
</verb></tscreen>
will cause to appear the word ``foo'' in the window, but you may store the pointer to any text in
<tt/r15/ (in this case) before call to DoDlgBox.
<p>
<tt/DB_GETSTR(x, y, ptr, length)/ - will add input from keyboard feature. <tt/ptr/ works as in
previous example and points to place where text is to be stored. Note that the contents of this
place will be shown upon creating window. <tt/length/ is the maximum number of characters to input.
<p>
<tt/DB_SYSOPV(ptr)/ - this sets <tt/otherPressVec/ to given pointer. It is called on every keypress.
<p>
<tt/DB_GRPHSTR(ptr)/ - data for this command is the pointer for <tt/GraphicsString/ commands.
<p>
<tt/DB_GETFILES(x, y)/ - for standard window you should pass 4 for both x and y. This function
draws file selection box and searches current drive for files. Before call to <tt/DoDlgBox/ you
must load <tt/r7L/ with GEOS filetype of searched files and <tt/r10/ with class text. In <tt/r5/
you have to load pointer to a <tt/char&lsqb;17&rsqb;/ where selected filename will be copied. It works
like <tt/FindFTypes/ but is limited to first 16 files.
<p>
<tt/DB_OPVEC(ptr)/ - this sets the new pointer for button press function, if you pass
<tt/RstrFrmDialogue/ here you will cause the window to close after pressing mouse button.
<p>
<tt/DB_USRICON(x, y, ptr)/ - places single user icon (click box) on window, <tt/ptr/ points at a
<tt/struct icondef/ but fields <tt/x/ and <tt/y/ are not used here. You can have at most 8 click
boxes in a window, this is internal limit of GEOS Kernal.
<p>
<tt/DB_USRROUT(ptr)/ - this command causes to immediately call user routine pointed by <tt/ptr/.

<sect2>GraphicsString command string
<p>
<tt/GraphicsString/ is a very powerful routine to initialize whole screen at once. There are
predefined macros for all commands, names are self-explanatory, see them in <tt/ggraph.h/. Last
command have to be <tt/GSTR_END/. There is custom type defined for the command string: <tt/graphicStr/.
<p>
Here is an example for clearing the screen:
<tscreen><verb>
const graphicStr example = &lcub;
        MOVEPENTO(0,0),
        NEWPATTERN(0),
        RECTANGLETO(319,199)
        GSTR_END &rcub;;
</verb></tscreen>

<sect2>InitRam table
<p>
This type of data is used to initialize one or more bytes in many places at once. The format is
as following:
<tscreen><verb>
void example = &lcub;
    (unsigned)address_to_store_values_at,
    (char)number_of_bytes_that_follow,
    (char)data,(char)data (...)
    (...) - more such definitions
    (unsigned)NULL - address of 0 ends the table
    &rcub;;
</verb></tscreen>

</article>