@c This file is part of the MIT/GNU Scheme Reference Manual.
@c $Id: win32-packaging.texi,v 1.2 2003/11/10 21:33:07 cph Exp $

@c Copyright 1991,1992,1993,1994,1995 Massachusetts Institute of Technology
@c Copyright 1996,1997,1999,2000,2001 Massachusetts Institute of Technology
@c Copyright 2002,2003 Massachusetts Institute of Technology
@c See file scheme.texinfo for copying conditions.

@node Win32 Package Reference, GNU Free Documentation License, Graphics, Top
@chapter Win32 Package Reference

@ifinfo
The Win32 implementation is still in a state of development.  It is
expected that changes will be necessary when MIT/GNU Scheme is ported to
Windows NT on the DEC Alpha architecture.  In particular, the
current system is not arranged in a way that adequately distinguishes 
between issues that are a consequence of the NT operating system and
those which are a consequence of the Intel x86 architecture.
@end ifinfo

@menu
* Win32 Package Overview::      
* Foreign function interface::  
* Device Independent Bitmap Utilities::  
@end menu


@node Win32 Package Overview, Foreign function interface, Win32 Package Reference, Win32 Package Reference
@section Overview


The Win32 implementation is still in a state of development.  It is
expected that changes will be necessary when MIT/GNU Scheme is ported to
Windows NT on the DEC Alpha architecture.  In particular, the
current system is not arranged in a way that adequately distinguishes
between issues that are a consequence of the NT operating system and
those which are a consequence of the Intel x86 architecture.
@cindex limitations

Thus this documentation is not definitive, it merely outlines how the
current system works.  Parts of the system will change and any project
implemented using the win32 system must plan for a re-implementation
stage.


The Win32 implementation has several components:

@itemize @bullet

@item
Special microcode primitives.

@item
A foreign function interface (FFI) for calling procedures in dynamically
linked libraries (DLLs).

@item
An interface for Edwin.

@item
The Win32 package provides support for using the features of the
Windows 3.1 and Windows NT 3.1 environments.

@item
Device Independent Bitmap utilities.  These are used by the win32 Scheme
Graphics implementation.  (The Scheme Graphics implementation is
described in the Reference Manual).

@end itemize

Note that all the names in the Win32 support are part of the
@code{win32} package.  The names are bound in the @code{(win32)}
environment, and do not appear as bindings in the user or root
environments.
An effect of this is that it is far easier to develop Win32 software in
the @code{(win32)} package environment or a child environment.

@node Foreign function interface, Device Independent Bitmap Utilities, Win32 Package Overview, Win32 Package Reference
@section Foreign Function Interface

The Win32 foreign function interface (FFI) is a primitive and fairly
simple system for calling procedures written in C in a
dynamically linked library (DLL).  Both user's procedures from a custom
DLL and system procedures (e.g.@: MessageBox) are called using the same
mechanism.

@cindex limitations
@strong{Warning}: The FFI as it stands has several flaws which make it
difficult to use reliably.  It is expected that both the interface to
and the mechanisms used by the FFI will be changed in the future.  We
provide it, and this documentation, only to give people an early start
in accessing some of the features of Win32 from Scheme.  Should you use
it in an experiment we welcome any feedback.

The FFI is designed for calling C procedures that use C data types
rather than Scheme data objects.  Thus it is not possible to write and
call a C procedure that returns, for example, a Scheme list.  The object
returned will always be an integer (which may represent the address of a
C data structure).

@cindex warning
@strong{Warning}: It is extremely dangerous to try to pass Scheme
callback procedures to C procedures.  It is only possible by passing
integer `handles' rather than the actual procedures, and even so, if a
garbage collection occurs during the execution of the callback procedure
objects in Scheme's heap will have moved.  Thus in a foreign procedure
that has a callback and a string, after calling the callback the string
value may no longer be valid.  Playing this game requires a profound
knowledge of the implementation.


The interface to the FFI has two main components: a language for
declaring the types of values passed to and returned from the foreign
procedures and a form for declaring foreign procedures.

@menu
* Windows Types::               
* Windows Foreign Procedures::  
* Win32 API names and procedures::  
@end menu

@node  Windows Types, Windows Foreign Procedures, Foreign function interface, Foreign function interface
@subsection Windows Types

@cindex Windows types
@cindex foreign type declarations
@cindex types, Windows
@cindex defining foreign types
Foreign types are designed to represent a correspondence between a
Scheme data type that is used to represent an object within the Scheme
world and a C data type that represents the data object in the C world.
Thus we cannot manipulate true C objects in Scheme, nor can we
manipulate Scheme objects in C.

Each foreign type has four aspects that together ensure that the
correspondence between the Scheme and C objects is maintained.  These
aspects are all encoded as procedures that either check for validity or
convert between representations.  Thus a foreign type is not a
declarative type so much as a procedural description of how to pass the
type.  The underlying foreign procedure call mechanism can pass integers
and vector-like Scheme objects, and returns integer values.  All other
objects must be translated into integers or some other basic type, and
must be recovered from integers.

The aspects are:

@table @var

@item check
A predicate that returns @code{#t} if the argument is of an acceptable
Scheme type, otherwise returns @code{#f}.
The @var{check} procedure is used for type-checking.

@item convert
A procedure of one argument which returns a Scheme object of one of the
basic types.
It is used to convert an object into a `simpler' object that will
eventually be converted into a C object.
The legal simpler objects are integers and strings.

@item return-convert
A procedure of one argument that, given an integer, returns a Scheme
object of a type satisfying @var{check}.
Its purpose is to convert the result returned by the foreign procedure
into a Scheme value.

@item revert
Some C procedures modify one or more of their arguments.  These
arguments are passed by reference, i.e.@: as a pointer to their address.
Since a Scheme object might have a different memory layout and storage
conventions, it must be passed by copy-in and copy-out rather than by
reference.
@var{Revert} is a procedure of two parameters, the original object
passed and the result of @var{convert} on that object.
@var{Revert} may then inspect the converted object and copy back the
changes to the original.

@end table

@deffn {special form} define-windows-type name check convert return revert
@deffnx {special form} define-similar-windows-type name model [check [convert [return [revert]]]]
@cindex defining foreign types
Both forms define a windows type.
The first form defines a type in terms of its aspects as described
above.
The second defines the type as being like another type, except for
certain aspects, which are redefined.
@var{Name} is the name of the type.
@var{Model} is the name of a type.
@var{Check}, @var{convert}, @var{return} and @var{revert} are
procedures or the value @code{#f}.
A @code{#f} means use the default value, which in the second form means
use the definition provided for @var{model}.
The defaults are

@table @var
@item check
@code{(lambda (x) #t)}, i.e.@: unchecked.
@item convert
@code{(lambda (x) x)}, i.e.@: no translation performed.
@item return
@code{(lambda (x) x)}, i.e.@: no translation performed.
@item revert
@code{(lambda (x y) unspecific)}, i.e.@: no update performed
@end table

The @code{unchecked} windows type (see below) is defined as:

@example
(define-windows-type unchecked #f #f #f #f)
@end example

Windows types are @emph{not} first class values, so they cannot be
stored in variables or defined using @code{define}:

@example
@group
(define my-type unchecked)            @error{}  Unbound variable
(define-similar-windows-type my-type unchecked)
                                      @r{;; the correct way}
@end group
@end example

Scheme characters must be converted to integers.  This is accomplished
as follows:

@example
@group
(define-windows-type char
   char?          @r{; check}
   char->integer  @r{; convert}
   integer->char  @r{; convert return value}
   #f             @r{; cannot be passed by reference}
)
@end group
@end example
@end deffn

@deffn {windows type} unchecked
The type which is not checked and undergoes only the basic conversion
from a Scheme integer to a C integer or from a Scheme string to a C
pointer to the first byte of the string.
Returned @code{unchecked} values are returned as integers.
@end deffn

@deffn {windows type} bool
Scheme booleans are analogous to C integers @code{0} and @code{1}.
Windows type @code{bool} have been defined as:

@example
@group
(define-windows-type bool
   boolean?
   (lambda (x) (if x 1 0))
   (lambda (x) (if (eq? x 0) #f #t))
   #f)
@end group
@end example
@end deffn

@deffn {windows type} char
Scheme characters are converted into C objects of type @code{char},
which are indistinguishable from small integers.
@end deffn

@deffn {windows type} int
@deffnx {windows type} uint
@deffnx {windows type} long
@deffnx {windows type} ulong
@deffnx {windows type} short
@deffnx {windows type} ushort
@deffnx {windows type} word
@deffnx {windows type} byte
Various integer types that are passed without conversion.
@end deffn

@deffn {windows type} string
A string that is passed as a C pointer of type @code{char*} to the first
character in the string.
@end deffn

@deffn {windows type} char*
A string or @code{#f}.  The string is passed as a pointer to characters.
The string is correctly null-terminated.  @code{#f} is passed as the null
pointer.  This is an example where there is a more complex mapping
between C objects and Scheme objects.  C's @code{char*} type is
represented as one of two Scheme types depending on its value.  This
allows us us to distinguish between the C string (pointer) that points
to the empty sequence of characters and the null pointer (which doesnt
point anywhere).
@end deffn

@deffn {windows type} handle
@deffnx {windows type} hbitmap
@deffnx {windows type} hbrush
@deffnx {windows type} hcursor
@deffnx {windows type} hdc
@deffnx {windows type} hicon
@deffnx {windows type} hinstance
@deffnx {windows type} hmenu
@deffnx {windows type} hpalette
@deffnx {windows type} hpen
@deffnx {windows type} hrgn
@deffnx {windows type} hwnd
Various kinds of Win32 handle.  These names correspond to the same, but
all uppercase, names in the Windows C language header files.  Win32 API
calls are the source of values of this type and the values are
meaningless except as arguments to other Win32 API calls.  Currently
these values are represented as integers but we expect that Win32
handles will in future be represented by allocated Scheme objects
(e.g.@: records) that will allow predicates (e.g.@: @code{hmenu?}) and
sensible interlocking with the garbage collector to free the programmer
of the current tedious allocation and deallocation of handles.
@end deffn

@deffn {windows type} resource-id
A Windows resource identifier is either a small integer or a string.
In C, this distinction is possible because pointers look like
larger integers, so a machine word representing a small integer can be
distinguished from a machine word that is a pointer to the text of the
name of the resource.
@end deffn


@node Windows Foreign Procedures, Win32 API names and procedures, Windows Types, Foreign function interface
@subsection Windows Foreign Procedures

Foreign procedures are declared as callable entry-points in a module,
usually a dynamically linked library (DLL).


@deffn procedure find-module name
@cindex loading DLLs
@cindex DLL, loading
Returns a module suitable for use in creating procedures with
@code{windows-procedure}.  @var{Name} is a string which is the name of a
DLL file.  Internally, @code{find-module} uses the @code{LoadLibrary}
Win32 API, so @var{name} should conform to the specifications for this
call.  @var{Name} should be either a full path name of a DLL, or the
name of a DLL that resides in the same directory as the Scheme binary
@file{SCHEME.EXE} or in the system directory.

The module returned is a description for the DLL, and the DLL need not
necessarily be linked at or immediately after this call.  DLL modules
are linked on need and unlinked before Scheme exits and when there
are no remaining references to entry points after a garbage-collection.
This behavior ensures that the Scheme system can run when a DLL is
absent, provided the DLL is not actually used (i.e.@: no attempt is made
to call a procedure in the DLL).
@end deffn


@defvr variable gdi32.dll
@cindex DLL, GDI32.DLL
This variable is bound to the module describing the @file{GDI32.DLL}
library, which contains the Win32 API graphics calls, e.g.@:
@code{LineTo}.
@end defvr

@defvr variable kernel32.dll
@cindex DLL, KERNEL32.DLL
This variable is bound to the module describing the @file{KERNEL32.DLL}
library.
@end defvr

@defvr variable user32.dll
@cindex DLL, USER32.DLL
This variable is bound to the module describing the @file{USER32.DLL}
library.  This module contains many useful Win32 API procedures, like
@code{MessageBox} and @code{SetWindowText}.
@end defvr


@deffn {special form} windows-procedure (name (parameter type) @dots{}) return-type module entry-name [options]
@cindex defining foreign procedures
This form creates a procedure, and could be thought of as
``foreign-named-lambda''.  The form creates a Scheme procedure that
calls the C procedure identified by the exported entry point
@var{entry-name} in the module identified by the value of @var{module}.
Both @var{entry-name} and @var{module} are evaluated at procedure
creation time, so either may be expression.  @var{Entry-name} must
evaluate to a string and @var{module} must evaluate to a module as
returned by @code{find-module}.
These are the only parts of the form that are evaluated at procedure
creation time.

@var{Name} is the name of the procedure and is for documentation
purposes only.  This form @emph{does not} define a procedure called
@var{name}.  It is more like @code{lambda}.  The name might be used for
debugging and pretty-printing.

A windows procedure has a fixed number of parameters (i.e.@: no `rest'
parameters or `varargs'), each of which is named and associated with a
windows type @var{type}.  Both the name @var{parameter} and the windows
type @var{type} must be symbols and are not evaluated.  The procedure
returns a value of the windows type @var{return-type}.

The following example creates a procedure that takes a window handle
(@code{hwnd}) and a string and returns a boolean (@code{bool}) result.
The procedure does this by calling the @code{SetWindowText} entry in the
module that is the value of the variable @code{user32.dll}.  The
variable @code{set-window-title} is defined to have this procedure as
it's value.

@example
@group
(define set-window-title
  (windows-procedure
   (set-window-text (window hwnd) (text string))
   bool user32.dll "SetWindowText"))

(set-window-title my-win "Hi")
                         @result{}  #t
                         @r{;; Changes window's title/text}

set-window-title         @result{}  #[compiled-procedure  @dots{}]
set-window-text          @error{}  Unbound variable
@end group
@end example


When there are no @var{options} the created procedure will (a) check its
arguments against the types, (b) convert the arguments, (c) call the C
procedure and (d) convert the returned value.  No reversion is
performed, even if one of the @var{types} has a reversion defined.
(Reverted types are rare [I have never used one], so paying a cost for
this unless it is used seems silly).

The following options are allowed:

@table @asis
@item @code{with-reversions}
The reversions are included in the type conversions.

@item @code{expand}
A synonym for @code{with-reversions}.

@item @var{Scheme code}
The @var{Scheme code} is placed between steps (a) and (b) in the default
process.  The Scheme code can enforce constraints on the arguments,
including constraints between arguments such as checking that an index
refers to a valid position in a string.
@end table

If both options (i.e.@: @code{with-reversions} and Scheme code) are used,
@code{with-reversions} must appear first.  There can be arbitrarily many
Scheme expression.
@end deffn

@node Win32 API names and procedures,  , Windows Foreign Procedures, Foreign function interface
@subsection Win32 API names and procedures

This section is a moving target.
@cindex Win32 API names
@cindex naming conventions

The @code{#define} values from @file{wingdi.h} and @file{winuser.h} are
available as bindings in the @code{(win32)} package environment.  The
@code{#define} symbols are all uppercase; these have been translated to
all lowercase Scheme identifiers, thus @code{WM_LBUTTONUP} is the scheme
variable @code{wm_lbuttonup}.  As Scheme is case insensitive, the
upper-case version may be used and probably should to make the code look
more like conventional Windows code.  The Scheme bindings have been
produced automagically.  Most of the @code{#define}-symbols contain an
underscore so there are not many name clashes.  There is one very
notable name clash, however: @code{ERROR} is @code{#define}d to 0, which
shadows the scheme procedure @code{error} in the root package
environment.  To signal an error, use @code{access} to get @code{error}
from the system global environment:

@example
@group
(declare (usual-integrations))
@dots{}
((access error system-global-environment) "Complain" @dots{})
@end group
@end example


The set of procedures is incomplete because procedures have been added
on a by-need basis for the implementation of other parts of the system,
e.g.@:  Scheme Graphics.  Look in the implementation for further details.

Win32 API procedure names have been uniformly converted into Scheme
identifiers as follows:

@itemize @bullet
@item
A leading uppercase letter is translated into a lowercase letter.
@item
Subsequent sequences of uppercase letters are translated into lowercase
letters preceeded by a hyphen (minus symbol), i.e.@: hyphens are inserted
at a lowercase to uppercase transition.
@item
Predicates beginning with @code{Is} finally have a
question-mark appended.
@end itemize

@noindent
Example: applying these rules to @code{IsWindow} yields
@code{is-window?}, and @code{GetDC} is translated into @code{get-dc}.


@c [It might be worthwhile just keeping the same names.  As the
@c Win32 API procedure names are uniformly `WordWordWordACRONYMWord', case
@c insensitivity is unlikely to be a problem.  The only problem is the
@c potential for a clash between a procedure name and a type
@c name.]


@node Device Independent Bitmap Utilities,  , Foreign function interface, Win32 Package Reference
@section Device Independent Bitmap Utilities


The Device Independent Bitmap (DIB) utilities library @file{DIBUTILS.DLL}
and the associated procedures in @file{dib.scm} in the Win32 system
source is an example of how to use the foreign function interface to
access and manipulate non-Scheme objects.
@cindex DLL, DIBUTILS.DLL

@deffn {windows type} dib
In the C world a DIB is a @dfn{handle} to a piece of memory containing
the bits that represent information about the image and the pixels of
the image.  The handle is a machine-word sized piece of data which may
be thought of as a 32 bit integer.  The handle may be null (i.e.@: zero),
indicating that there is no block of memory describing the DIB.  The
null value is usually returned by C functions that are supposed to
create a DIB but failed, for some reason like the memory could not be
allocated or a file could not be opened.

In the Scheme world a DIB is a structure containing information
about the bitmap (specifically the integer that represents the handle).
We also include @code{#f} in the @code{dib} windows type to mirror the
null handle error value.

@example
@group
(define dib-result
  (lambda (handle)
    (if (= handle 0)
        #f
        (make-dib handle))))

(define dib-arg
  (lambda (dib)
    (if dib
        (cell-contents (dib-handle dib))
        0)))  

(define-windows-type dib
  (lambda (thing) (or (dib? thing) (eq? thing #f)))
  dib-arg
  dib-result)
@end group
@end example
@end deffn


@menu
* DIB procedures::              
* Other parts of the DIB Utilities implementation::  
@end menu

@node DIB procedures, Other parts of the DIB Utilities implementation, Device Independent Bitmap Utilities, Device Independent Bitmap Utilities
@subsection DIB procedures

The following procedures have typed parameters, using the same
convention as @code{windows-procedure}.

@deffn procedure open-dib (filename string)
Return type: @var{dib}.  Calls the @code{OpenDIB} entry of
@file{DIBUTILS.DLL}.  If the return value is not @code{#f} then the file
@var{filename} was found, successfully opened, and the contents were
suitable for loading into memory as a device independent bitmap.
@end deffn

@deffn procedure write-dib (filename string) (dib dib) 
Return type: @var{bool}.  Calls the @code{WriteDIB} entry of
@file{DIBUTILS.DLL}.  Returns @code{#t} if the file @var{filename} could
be opened and written to.  After this operation the file contains the
bitmap data in a standard format that is understood by @code{open-dib}
and various system utilities like the bitmap editor.  Any problems
resulting in failure are signalled by a @code{#f} return value.
@end deffn

@deffn procedure bitmap-from-dib (dib dib) (palette hpalette)
Return type: @var{hbitmap}.
Calls the @code{BitmapFromDib} entry of @file{DIBUTILS.DLL}.  The returned
value is a device dependent bitmap.  The colours from the DIB are
matched against colors in @var{palette}.
@end deffn

@deffn procedure dib-from-bitmap (bitmap hbitmap) (style dword) (bits word) (palette hpalette)
Return type: @var{dib}.
Returns a DIB containing the same image as the device dependent bitmap
@var{bitmap}.
@var{Style} determines the kind of DIB, e.g.@: compression style.
Calls the @code{DibFromBitmap} entry of @file{DIBUTILS.DLL}.
@end deffn

@deffn procedure dib-blt (dest hdc) (x int) (y int) (w int) (h int) (src dib) (src-x int) (src-y int) (raster-op long)
Return type: @var{bool}.  Calls the @code{DibBlt} entry of
@file{DIBUTILS.DLL}.  Similar to the Win32 API @code{BitBlt} call, but
draws a DIB rather than a piece of another device context.  Draws the
@var{dib} on device context @var{hdc} at position (@var{x},@var{y}).  A
rectangle of width @var{w} and height @var{h} is copied from position
(@var{src-x},@var{src-y}) of @var{dib}.
@var{Raster-op} is supposed to allow the source and destination to be
combined but I don't think I got this right so stick to @code{SRCCOPY}.
@end deffn

@deffn procedure delete-dib (dib dib)
Return type: @var{bool}.
This procedure reclaims the storage occupied by a DIB.
After being deleted, the DIB should not be used.
This procedure allows the programmer to reclaim external heap storage
rather than risking it running out before the next garbage collection.
@end deffn

@deffn procedure dib-height (dib dib)
Return type: @var{int}.
Calls the @code{DibHeight} expand entry of @file{DIBUTILS.DLL}, which returns
the height of the bitmap in pixels.
@end deffn

@deffn procedure dib-width (dib dib)
Return type: @var{int}.
Calls the @code{DibWidth} entry of @file{DIBUTILS.DLL}, which returns
the width of the bitmap in pixels.
@end deffn

@deffn procedure copy-bitmap (bm hbitmap)
Return type: @var{hbitmap}.
Calls the @code{CopyBitmap} of @file{DIBUTILS.DLL}, which creates a new
bitmap with the same size and contents as the original.
@end deffn

@deffn procedure create-dib (width int) (height int) (style int) (depth int) (palette hpalette)
Return type: @var{dib}.
Calls the @code{CreateDIB} entry of @file{DIBUTILS.DLL}.
Creates a DIB of @var{width} by @var{height} pixels and @var{depth} bits
of colour information.
The @var{style} parameter determines how the bitmap is stored.
I have only ever used @code{BI_RGB}.
If @var{depth}<=8 then the @var{palette} determines the DIB's colour table.
@end deffn

@deffn procedure crop-bitmap (bm hbitmap) (left int) (top int) (right int) (bottom int)
Return type: @var{hbitmap}.
Calls the @code{CropBitmap} entry of @file{DIBUTILS.DLL}.
Returns a new bitmap containing the image from a region of the original.
@end deffn

@deffn procedure dib-set-pixels-unaligned dib (pixels string)
Return type: @var{bool}.
Calls the @code{DIBSetPixelsUnaligned} entry of@* @file{DIBUTILS.DLL}.  Stuffs
bytes from @var{pixels} into the bitmap.  There are no alignment
constraints on @var{pixels} (the usual way of doing this is to use the
@code{SetDIBits} function which requires that every scan line of the
bitmap is 32-bit word aligned, even if the scan lines are not a multiple
of 4 bytes long).  doing this
@end deffn

@node Other parts of the DIB Utilities implementation,  , DIB procedures, Device Independent Bitmap Utilities
@subsection Other parts of the DIB Utilities implementation


The @file{DIBUTILS.DLL} library is an ordinary DLL.  See the standard
Microsoft Windows documentation on how to create DLLs.  Look at the code
in the @file{WIN32/DIBUTILS} directory of the Scheme source.

Please note:
@itemize @bullet
@item
@cindex DLL, exports
For the foreign function interface to find the procedures they must be
declared as exports in the @file{.DEF} definition file.

@item
To load the @file{.DLL} file use the @code{find-module} Scheme function.
Look at @file{WIN32/DIB.SCM} to see how this is done.

@item
The current system works with C procedures with the @code{__stdcall} and
@code{__cdecl} calling conventions but @emph{not} the @code{__fastcall}
calling convention.
@end itemize
