quakeforge/tools/qfcc/doc/qcc.txt

Copyright (C) 1996-1997  Id Software, Inc.

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it under the terms of the GNU General Public License as published by
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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See file, 'COPYING', for details.

$Id$


comments
--------
// comments discard text until the end of line
/*  */ comments discard all enclosed text (spaced out on this line
because this documentation is in a regular C comment block, and typing
them in normally causes a parse error)

code structure
--------------
A definition is:
	<type> <name> [ = <immediate>] {, <name> [ = <immediate>] };


types
-----
simple types: void, float, vector, string, or entity
	float		width, height;
	string		name;
	entity		self, other;

vector types:
	vector		org;	// also creates org_x, org_y, and org_z float defs
	
	
A function type is specified as: 	simpletype ( type name {,type name} )
The names are ignored except when the function is initialized.	
	void()		think;
	entity()	FindTarget;
	void(vector destination, float speed, void() callback)	SUB_CalcMove;
	void(...)	dprint;		// variable argument builtin

A field type is specified as:  .type
	.vector		origin;
	.string		netname;
	.void()		think, touch, use;
	

names
-----
Names are a maximum of 64 characters, must begin with A-Z,a-z, or _, and
can continue with those characters or 0-9.

There are two levels of scoping: global, and function.  The parameter list
of a function and any vars declared inside a function with the "local"
statement are visible only within that function, 


immediates
----------
Float immediates must begin with 0-9 or minus sign.  .5 is illegal.
	
A parsing ambiguity is present with negative constants. "a-5" will be
parsed as "a", then "-5", causing an error.  Seperate the - from the
digits with a space "a - 5" to get the proper behavior.
	12
	1.6
	0.5
	-100

Vector immediates are three float immediates enclosed in single quotes.
	'0 0 0'
	'20.5 -10 0.00001'
	
String immediates are characters enclosed in double quotes.  The string
cannot contain explicit newlines, but the escape character \n can embed
one.  The \" escape can be used to include a quote in the string.
	"maps/jrwiz1.bsp"
	"sound/nin/pain.wav"
	"ouch!\n"

Code immediates are statements enclosed in {} braces.
statement:
	{ <multiple statements> }
	<expression>;
	local <type> <name> [ = <immediate>] {, <name> [ = <immediate>] };
	return <expression>;
	if ( <expression> ) <statement> [ else <statement> ];
	while ( <expression> ) <statement>;
	do <statement> while ( <expression> );
	<function name> ( <function parms> );
	
expression:
	combiations of names and these operators with standard C precedence:
	"&&", "||", "<=", ">=","==", "!=", "!", "*", "/", "-", "+", "=", ".",
	"<", ">", "&", "|"
	Parenthesis can be used to alter order of operation.
	The & and | operations perform integral bit ops on floats
	
A built in function immediate is a number sign followed by an integer.
	#1
	#12


compilation
-----------
Source files are processed sequentially without dumping any state, so if a
defs file is the first one processed, the definitions will be available to
all other files.

The language is strongly typed and there are no casts.

Anything that is initialized is assumed to be constant, and will have
immediates folded into it.  If you change the value, your program will
malfunction.  All uninitialized globals will be saved to savegame files.

Functions cannot have more than eight parameters.

Error recovery during compilation is minimal.  It will skip to the next
global definition, so you will never see more than one error at a time in
a given function.  All compilation aborts after ten error messages.

Names can be defined multiple times until they are defined with an
initialization, allowing functions to be prototyped before their
definition.

void()	MyFunction;			// the prototype

void()	MyFunction =		// the initialization
{
	dprint ("we're here\n");
};


entities and fields
-------------------


execution
---------
Code execution is initiated by C code in quake from two main places:  the
timed think routines for periodic control, and the touch function when two
objects impact each other.

There are three global variables that are set before beginning code
execution:
	entity	world;		// the server's world object, which holds all
						// global state for the server, like the
						// deathmatch flags and the body ques.
	entity	self;		// the entity the function is executing for
	entity	other;		// the other object in an impact, not used for
						// thinks
	float	time;		// the current game time.  Note that because the
						// entities in the world are simulated
						// sequentially, time is NOT strictly increasing.
						// An impact late in one entity's time slice may
						// set time higher than the think function of the
						// next entity.  The difference is limited to 0.1
						// seconds.
Execution is also caused by a few uncommon events, like the addition of a
new client to an existing server.
	
There is a runnaway counter that stops a program if 100000 statements are
executed, assuming it is in an infinite loop.

It is acceptable to change the system set global variables.  This is
usually done to pose as another entity by changing self and calling a
function.

The interpretation is fairly efficient, but it is still over an order of
magnitude slower than compiled C code.  All time consuming operations
should be made into built in functions.

A profile counter is kept for each function, and incremented for each
interpreted instruction inside that function.  The "profile" console
command in Quake will dump out the top 10 functions, then clear all the
counters.  The "profile all" command will dump sorted stats for every
function that has been executed.


afunc ( 4, bfunc(1,2,3));
will fail because there is a shared parameter marshaling area, which will
cause the 1 from bfunc to overwrite the 4 already placed in parm0.  When
a function is called, it copies the parms from the globals into it's
privately scoped variables, so there is no collision when calling another
function.

total = factorial(3) + factorial(4);
Will fail because the return value from functions is held in a single
global area.  If this really gets on your nerves, tell me and I can work
around it at a slight performance and space penalty by allocating a new
register for the function call and copying it out.


built in functions
------------------
void(string text)	dprint;
Prints the string to the server console.

void(entity client, string text)	cprint;
Prints a message to a specific client.

void(string text)	bprint;
Broadcast prints a message to all clients on the current server.

entity()	spawn;
Returns a totally empty entity.  You can manually set everything up, or
just set the origin and call one of the existing entity setup functions.

entity(entity start, .string field, string match) find;
Searches the server entity list beginning at start, looking for an entity
that has entity.field = match.  To start at the beginning of the list,
pass world.  World is returned when the end of the list is reached.

<FIXME: define all the other functions...>


gotchas
-------
o	The && and || operators DO NOT EARLY OUT like C!
o	Don't confuse single quoted vectors with double quoted strings
o	The function declaration syntax takes a little getting used to.
o	Don't forget the ; after the trailing brace of a function
	initialization.
o	Don't forget the "local" before defining local variables.
o	There are no ++ / -- operators, or operate/assign operators.