grub/docs/grub-dev.texi

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@c -*-texinfo-*-
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@setfilename grub-dev.info
@include version-dev.texi
@settitle GNU GRUB Developers Manual @value{VERSION}
@c Unify all our little indices for now.
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@copying
This developer manual is for GNU GRUB (version @value{VERSION},
@value{UPDATED}).

Copyright @copyright{} 1999,2000,2001,2002,2004,2005,2006,2008,2009,2010,2011 Free Software Foundation, Inc.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no
Invariant Sections.
@end quotation
@end copying

@dircategory Kernel
@direntry
* grub-dev: (grub-dev).                 The GRand Unified Bootloader Dev
@end direntry

@setchapternewpage odd

@titlepage
@sp 10
@title the GNU GRUB developer manual
@subtitle The GRand Unified Bootloader, version @value{VERSION}, @value{UPDATED}.
@author Yoshinori K. Okuji
@author Colin D Bennett
@author Vesa Jääskeläinen
@author Colin Watson
@author Robert Millan 
@author Carles Pina
@c The following two commands start the copyright page.
@page
@vskip 0pt plus 1filll
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@end titlepage

@c Output the table of contents at the beginning.
@contents

@finalout
@headings double

@ifnottex
@node Top
@top GNU GRUB developer manual

This is the developer documentation of GNU GRUB, the GRand Unified Bootloader,
a flexible and powerful boot loader program for a wide range of
architectures.

This edition documents version @value{VERSION}.

@insertcopying
@end ifnottex

@menu
* Getting the source code::
* Finding your way around::
* Coding style::
* Contributing Changes::
* Error Handling::
* CIA::
* BIOS port memory map::
* Video Subsystem::
* PFF2 Font File Format::
* Graphical Menu Software Design::
* Copying This Manual::         Copying This Manual
* Index::
@end menu


@node Getting the source code
@chapter Getting the source code

GRUB is maintained using the @uref{http://bazaar-vcs.org/, Bazaar revision
control system}.  To fetch the primary development branch:

@example
bzr get http://bzr.savannah.gnu.org/r/grub/trunk/grub
@end example

The GRUB developers maintain several other branches with work in progress.
Of these, the most interesting is the experimental branch, which is a
staging area for new code which we expect to eventually merge into trunk but
which is not yet ready:

@example
bzr get http://bzr.savannah.gnu.org/r/grub/branches/experimental
@end example

Once you have used @kbd{bzr get} to fetch an initial copy of a branch, you
can use @kbd{bzr pull} to keep it up to date.  If you have modified your
local version, you may need to resolve conflicts when pulling.

@node Coding style
@chapter Coding style
@c By YoshinoriOkuji, VesaJääskeläinen and ColinBennett

Basically we follow the @uref{http://www.gnu.org/prep/standards_toc.html, GNU Coding Standards}. We define additional conventions for GRUB here.

@menu
* Naming Conventions::
* Functions::
* Variables::
* Types::
* Macros::
* Comments::
* Multi-Line Comments::
@end menu

@node Naming Conventions
@section Naming Conventions

All global symbols (i.e. functions, variables, types, and macros) must have the prefix grub_ or GRUB_. The all capital form is used only by macros.

@node Functions
@section Functions

If a function is global, its name must be prefixed with grub_ and must consist of only small letters. If the function belongs to a specific function module, the name must also be prefixed with the module name. For example, if a function is for file systems, its name is prefixed with grub_fs_. If a function is for FAT file system but not for all file systems, its name is prefixed with grub_fs_fat_. The hierarchy is noted this way.

After a prefix, a function name must start with a verb (such as get or is). It must not be a noun. Some kind of abbreviation is permitted, as long as it wouldn't make code less readable (e.g. init).

If a function is local, its name may not start with any prefix. It must start with a verb.

@node Variables
@section Variables

The rule is mostly the same as functions, as noted above. If a variable is global, its name must be prefixed with grub_ and must consist of only small letters. If the variable belongs to a specific function module, the name must also be prefixed with the module name. For example, if a function is for dynamic loading, its name is prefixed with grub_dl_. If a variable is for ELF but not for all dynamic loading systems, its name is prefixed with grub_dl_elf_.

After a prefix, a variable name must start with a noun or an adjective (such as name or long) and it should end with a noun. Some kind of abbreviation is permitted, as long as it wouldn't make code less readable (e.g. i18n).

If a variable is global in the scope of a single file (i.e. it is declared with static), its name may not start with any prefix. It must start with a noun or an adjective.

If a variable is local, you may choose any shorter name, as long as it wouldn't make code less readable (e.g. i).

@node Types
@section Types

The name of a type must be prefixed with grub_ and must consist of only small letters. If the type belongs to a specific function module, the name must also be prefixed with the module name. For example, if a type is for OS loaders, its name is prefixed with grub_loader_. If a type is for Multiboot but not for all OS loaders, its name is prefixed with grub_loader_linux_.

The name must be suffixed with _t, to emphasize the fact that it is a type but not a variable or a function.

@node Macros
@section Macros

If a macro is global, its name must be prefixed with GRUB_ and must consist of only large letters. Other rules are the same as functions or variables, depending on whether a macro is used like a function or a variable.

@node Comments
@section Comments

All comments shall be C-style comments, of the form @samp{/* @dots{} */}.

Comments shall be placed only on a line by themselves.  They shall not be placed together with code, variable declarations, or other non-comment entities.  A comment should be placed immediately preceding the entity it describes.

Acceptable:
@example
/* The page # that is the front buffer.  */
int displayed_page;
/* The page # that is the back buffer.  */
int render_page;
@end example

Unacceptable:
@example
int displayed_page;           /* The page # that is the front buffer. */
int render_page;              /* The page # that is the back buffer. */
@end example

@node Multi-Line Comments
@section Multi-Line Comments

Comments spanning multiple lines shall be formatted with all lines after the first aligned with the first line.  

Asterisk characters should not be repeated a the start of each subsequent line.

Acceptable:
@example
/* This is a comment
   which spans multiple lines.
   It is long.  */
@end example

Unacceptable:
@example
/*
 * This is a comment
 * which spans multiple lines.
 * It is long. */
@end example

The opening @samp{/*} and closing @samp{*/} should be placed together on a line with text.

@node Finding your way around
@chapter Finding your way around

Here is a brief map of the GRUB code base.

GRUB uses Autoconf and Automake, with most of the Automake input generated
by AutoGen.  The top-level build rules are in @file{configure.ac},
@file{grub-core/Makefile.core.def}, and @file{Makefile.util.def}.  Each
block in a @file{*.def} file represents a build target, and specifies the
source files used to build it on various platforms.  The @file{*.def} files
are processed into AutoGen input by @file{gentpl.py} (which you only need to
look at if you are extending the build system).  If you are adding a new
module which follows an existing pattern, such as a new command or a new
filesystem implementation, it is usually easiest to grep
@file{grub-core/Makefile.core.def} and @file{Makefile.util.def} for an
existing example of that pattern to find out where it should be added.

In general, code that may be run at boot time is in a subdirectory of
@file{grub-core}, while code that is only run from within a full operating
system is in a subdirectory of the top level.

Low-level boot code, such as the MBR implementation on PC BIOS systems, is
in the @file{grub-core/boot/} directory.

The GRUB kernel is in @file{grub-core/kern/}.  This contains core facilities
such as the device, disk, and file frameworks, environment variable
handling, list processing, and so on.  The kernel should contain enough to
get up to a rescue prompt.  Header files for kernel facilities, among
others, are in @file{include/}.

Terminal implementations are in @file{grub-core/term/}.

Disk access code is spread across @file{grub-core/disk/} (for accessing the
disk devices themselves), @file{grub-core/partmap/} (for interpreting
partition table data), and @file{grub-core/fs/} (for accessing filesystems).
Note that, with the odd specialised exception, GRUB only contains code to
@emph{read} from filesystems and tries to avoid containing any code to
@emph{write} to filesystems; this lets us confidently assure users that GRUB
cannot be responsible for filesystem corruption.

PCI and USB bus handling is in @file{grub-core/bus/}.

Video handling code is in @file{grub-core/video/}.  The graphical menu
system uses this heavily, but is in a separate directory,
@file{grub-core/gfxmenu/}.

Most commands are implemented by files in @file{grub-core/commands/}, with
the following exceptions:

@itemize
@item
A few core commands live in @file{grub-core/kern/corecmd.c}.

@item
Commands related to normal mode live under @file{grub-core/normal/}.

@item
Commands that load and boot kernels live under @file{grub-core/loader/}.

@item
The @samp{loopback} command is really a disk device, and so lives in
@file{grub-core/disk/loopback.c}.

@item
The @samp{gettext} command lives under @file{grub-core/gettext/}.

@item
The @samp{loadfont} and @samp{lsfonts} commands live under
@file{grub-core/font/}.

@item
The @samp{serial}, @samp{terminfo}, and @samp{background_image} commands
live under @file{grub-core/term/}.

@item
The @samp{efiemu_*} commands live under @file{grub-core/efiemu/}.
@end itemize

There are a few other special-purpose exceptions; grep for them if they
matter to you.

Utility programs meant to be run from a full operating system are in
@file{util/}.

@node Contributing Changes
@chapter Contributing changes
@c By YoshinoriOkuji, VesaJääskeläinen, ColinWatson

Contributing changes to GRUB 2 is welcomed activity. However we have a
bit of control what kind of changes will be accepted to GRUB 2.
Therefore it is important to discuss your changes on grub-devel mailing list
(see MailingLists). On this page there are some basic details on the
development process and activities.

First of all you should come up with the idea yourself what you want to
contribute. If you do not have that beforehand you are advised to study this
manual and try GRUB 2 out to see what you think is missing from there.

Here are additional pointers:
@itemize
@item @url{https://savannah.gnu.org/task/?group=grub GRUB's Task Tracker}
@item @url{https://savannah.gnu.org/bugs/?group=grub GRUB's Bug Tracker}
@end itemize

If you intended to make changes to GRUB Legacy (<=0.97) those are not accepted
anymore.

@menu
* Getting started::
* Typical Developer Experience::
* When you are approved for write access to project's files::
@end menu

@node Getting started
@section Getting started

@itemize
@item Always use latest GRUB 2 source code. So get that first.

For developers it is recommended always to use the newest development version of GRUB 2. If development takes a long period of time, please remember to keep in sync with newest developments regularly so it is much easier to integrate your change in the future. GRUB 2 is being developed in a Bazaar (bzr) repository.

Please check Savannah's GRUB project page for details how to get newest bzr:
@uref{http://savannah.gnu.org/bzr/?group=grub, GRUB 2 bzr Repository}

@item Compile it and try it out.

It is always good idea to first see that things work somehow and after that
to start to implement new features or develop fixes to bugs.

@item Study the code.

There are sometimes odd ways to do things in GRUB 2 code base.
This is mainly related to limited environment where GRUB 2 is being executed.
You usually do not need to understand it all so it is better to only try to
look at places that relates to your work. Please do not hesitate to ask for
help if there is something that you do not understand.

@item Develop a new feature.

Now that you know what to do and how it should work in GRUB 2 code base, please
be free to develop it. If you have not so far announced your idea on grub-devel
mailing list, please do it now. This is to make sure you are not wasting your
time working on the solution that will not be integrated to GRUB 2 code base.

You might want to study our coding style before starting development so you
do not need to change much of the code when your patch is being reviewed.
(see @ref{Coding style})

For every accepted patch there has to exist a ChangeLog entry. Our ChangeLog
consist of changes within source code and are not describing about what the
change logically does. Please see examples from previous entries.

Also remember that GRUB 2 is licensed under GPLv3 license and that usually
means that you are not allowed to copy pieces of code from other projects.
Even if the source project's license would be compatible with GPLv3, please
discuss it beforehand on grub-devel mailing list.

@item Test your change.

Test that your change works properly. Try it out a couple of times, preferably on different systems, and try to find problems with it.

@item Publish your change.

When you are happy with your change, first make sure it is compilable with
latest development version of GRUB 2. After that please send a patch to
grub-devel for review. Please describe in your email why you made the change,
what it changes and so on. Please be prepared to receive even discouraging
comments about your patch. There is usually at least something that needs
to be improved in every patch.

Please use unified diff to make your patch (good match of arguments for diff is @samp{-pruN}).

@item Respond to received feedback.

If you are asked to modify your patch, please do that and resubmit it for
review. If your change is large you are required to submit a copyright
agreement to FSF. Please keep in mind that if you are asked to submit
for copyright agreement, process can take some time and is mandatory
in order to get your changes integrated.

If you are not on grub-devel to respond to questions, most likely your patch
will not be accepted. Also if problems arise from your changes later on,
it would be preferable that you also fix the problem. So stay around
for a while.

@item Your patch is accepted.

Good job! Your patch will now be integrated into GRUB 2 mainline, and if it didn't break anything it will be publicly available in the next release.

Now you are welcome to do further improvements :)
@end itemize

@node Typical Developer Experience
@section Typical Developer Experience

The typical experience for a developer in this project is the following:

@enumerate
@item You find yourself wanting to do something (e.g. fixing a bug).
@item You show some result in the mailing list or the IRC.
@item You are getting to be known to other developers.
@item You accumulate significant amount of contribution, so copyright assignment is processed.
@item You are free to check in your changes on your own, legally speaking.
@end enumerate

At this point, it is rather annoying that you ought to ask somebody else every
change to be checked in. For efficiency, it is far better, if you can commit
it yourself. Therefore, our policy is to give you the write permission to our
official repository, once you have shown your skill and will,
and the FSF clerks have dealt with your copyright assignment.

@node When you are approved for write access to project's files
@section When you are approved for write access to project's files

As you might know, GRUB is hosted on
@url{https://savannah.gnu.org/projects/grub Savannah}, thus the membership
is managed by Savannah. This means that, if you want to be a member of this
project:

@enumerate
@item You need to create your own account on Savannah.
@item You can submit ``Request for Inclusion'' from ``My Groups'' on Savannah.
@end enumerate

Then, one of the admins can approve your request, and you will be a member.
If you don't want to use the Savannah interface to submit a request, you can
simply notify the admins by email or something else, alternatively. But you
still need to create an account beforehand.

NOTE: we sometimes receive a ``Request for Inclusion'' from an unknown person.
In this case, the request would be just discarded, since it is too dangerous
to allow a stranger to be a member, which automatically gives him a commit
right to the repository, both for a legal reason and for a technical reason. 

If your intention is to just get started, please do not submit a inclusion
request. Instead, please subscribe to the mailing list, and communicate first
(e.g. sending a patch, asking a question, commenting on another message...).

@node Error Handling
@chapter Error Handling

Error handling in GRUB 2 is based on exception handling model. As C language
doesn't directly support exceptions, exception handling behavior is emulated
in software. 

When exception is raised, function must return to calling function. If calling
function does not provide handling of the exception it must return back to its
calling function and so on, until exception is handled. If exception is not
handled before prompt is displayed, error message will be shown to user.

Exception information is stored on @code{grub_errno} global variable. If
@code{grub_errno} variable contains value @code{GRUB_ERR_NONE}, there is no active
exception and application can continue normal processing. When @code{grub_errno} has
other value, it is required that application code either handles this error or
returns instantly to caller. If function is with return type @code{grub_err_t} is
about to return @code{GRUB_ERR_NONE}, it should not set @code{grub_errno} to that
value. Only set @code{grub_errno} in cases where there is error situation. 

Simple exception forwarder.
@example
grub_err_t
forwarding_example (void)
@{
  /* Call function that might cause exception.  */
  foobar ();

  /* No special exception handler, just forward possible exceptions.  */
  if (grub_errno != GRUB_ERR_NONE)
    @{
      return grub_errno;
    @}

  /* All is OK, do more processing.  */

  /* Return OK signal, to caller.  */
  return GRUB_ERR_NONE;
@}
@end example

Error reporting has two components, the actual error code (of type
@code{grub_err_t}) and textual message that will be displayed to user. List of
valid error codes is listed in header file @file{include/grub/err.h}. Textual
error message can contain any textual data. At time of writing, error message
can contain up to 256 characters (including terminating NUL). To ease error
reporting there is a helper function @code{grub_error} that allows easier
formatting of error messages and should be used instead of writing directly to
global variables.

Example of error reporting.
@example
grub_err_t
failing_example ()
@{
  return grub_error (GRUB_ERR_FILE_NOT_FOUND, 
                     "Failed to read %s, tried %d times.",
                     "test.txt",
                     10);
@}
@end example

If there is a special reason that error code does not need to be taken account,
@code{grub_errno} can be zeroed back to @code{GRUB_ERR_NONE}. In cases like this all
previous error codes should have been handled correctly. This makes sure that
there are no unhandled exceptions.

Example of zeroing @code{grub_errno}.
@example
grub_err_t
probe_example ()
@{
  /* Try to probe device type 1.  */
  probe_for_device ();
  if (grub_errno == GRUB_ERR_NONE)
    @{
      /* Device type 1 was found on system.  */
      register_device ();
      return GRUB_ERR_NONE;
    @}
  /* Zero out error code.  */
  grub_errno = GRUB_ERR_NONE;

  /* No device type 1 found, try to probe device type 2.  */
  probe_for_device2 ();
  if (grub_errno == GRUB_ERR_NONE)
    @{
      /* Device type 2 was found on system.  */
      register_device2 ();
      return GRUB_ERR_NONE;
    @}
  /* Zero out error code.  */
  grub_errno = GRUB_ERR_NONE;

  /* Return custom error message.  */
  return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "No device type 1 or 2 found.");
@}
@end example

Some times there is a need to continue processing even if there is a error
state in application. In situations like this, there is a needed to save old
error state and then call other functions that might fail. To aid in this,
there is a error stack implemented. Error state can be pushed to error stack
by calling function @code{grub_error_push ()}. When processing has been completed,
@code{grub_error_pop ()} can be used to pop error state from stack. Error stack
contains predefined amount of error stack items. Error stack is protected for
overflow and marks these situations so overflow error does not get unseen.
If there is no space available to store error message, it is simply discarded
and overflow will be marked as happened. When overflow happens, it most likely
will corrupt error stack consistency as for pushed error there is no matching
pop, but overflow message will be shown to inform user about the situation.
Overflow message will be shown at time when prompt is about to be drawn.

Example usage of error stack.
@example
/* Save possible old error message.  */
grub_error_push ();

/* Do your stuff here.  */
call_possibly_failing_function ();

if (grub_errno != GRUB_ERR_NONE)
  @{
    /* Inform rest of the code that there is error (grub_errno
       is set). There is no pop here as we want both error states 
       to be displayed.  */
    return;
  @}

/* Restore old error state by popping previous item from stack. */
grub_error_pop ();
@end example

@node CIA
@chapter CIA
@c By Robert Millan and Carles Pina
If you have commit access, please setup CIA in your Bazaar
config so those in IRC receive notification of your commits.

In @file{~/.bazaar/bazaar.conf}, add "cia_send_revno = true". 
Optionally, you can also add "cia_user = myusername" if you'd
like CIA service to use a specific account (for statistical purpose).

In the @file{.bzr/branch/branch.conf} of your checkout branch,
"set nickname = /path_to_this_branch" and "cia_project = GNU GRUB".

Additionally, please set cia_send_revno in the [DEFAULT] section
of your @file{~/.bazaar/bazaar.conf}. E.g.:

@example
[DEFAULT]
cia_send_revno = true
@end example

Remember to install cia-clients (Debian/Ubuntu package) to be able to use CIA.

Keep in mind Bazaar sends notifications for all commits to branches that have
this setting, regardless of whether they're bound branches (checkouts) or not.
So if you make local commits in a non-bound branch and it bothers you that
others can read them, do not use this setting.

@node BIOS port memory map
@chapter BIOS port memory map
@c By Yoshinori K Okuji

@multitable @columnfractions .15 .25 .5
@headitem Start @tab End @tab Usage
@item 0        @tab 0x1000 - 1   @tab BIOS and real mode interrupts 
@item 0x07BE   @tab 0x07FF       @tab Partition table passed to another boot loader 
@item ?        @tab 0x2000 - 1   @tab Real mode stack 
@item 0x7C00   @tab 0x7D00 - 1   @tab Boot sector 
@item 0x8000   @tab ?            @tab GRUB kernel 
@item 0x68000  @tab 0x78000 - 1  @tab Disk buffer 
@item ?        @tab 0x80000 - 1  @tab Protected mode stack 
@item 0x80000  @tab ?            @tab Heap 
@item ?        @tab 0xA0000 - 1  @tab Extended BIOS Data Area 
@item 0xA0000  @tab 0xC0000 - 1  @tab Video RAM 
@item 0xC0000  @tab 0x100000 - 1 @tab BIOS 
@item 0x100000 @tab ?            @tab Heap and module code 
@end multitable

@node Video Subsystem
@chapter Video Subsystem
@c By VesaJääskeläinen
This document contains specification for Video Subsystem for GRUB2.
Currently only the usage interface is described in this document.
Internal structure of how video drivers are registering and how video
driver manager works are not included here.

@menu
* Video API::
* Bitmap API::
* Example usage of Video API::
@end menu

@node Video API
@section Video API

@subsection grub_video_setup

@itemize
@item Prototype:
@example
grub_err_t
grub_video_setup (unsigned int width, unsigned int height, unsigned int mode_type);
@end example
@item Description:

Driver will use information provided to it to select best possible video mode and switch to it. Supported values for @code{mode_type} are @code{GRUB_VIDEO_MODE_TYPE_INDEX_COLOR} for index color modes, @code{GRUB_VIDEO_MODE_TYPE_RGB} for direct RGB color modes and @code{GRUB_VIDEO_MODE_TYPE_DOUBLE_BUFFERED} for double buffering. When requesting RGB mode, highest bits per pixel mode will be selected. When requesting Index color mode, mode with highest number of colors will be selected. If all parameters are specified as zero, video adapter will try to figure out best possible mode and initialize it, platform specific differences are allowed here. If there is no mode matching request, error X will be returned. If there are no problems, function returns @code{GRUB_ERR_NONE}.

This function also performs following task upon succesful mode switch. Active rendering target is changed to screen and viewport is maximized to allow whole screen to be used when performing graphics operations. In RGB modes, emulated palette gets 16 entries containing default values for VGA palette, other colors are defined as black. When switching to Indexed Color mode, driver may set default VGA palette to screen if the video card allows the operation.

@end itemize

@subsection grub_video_restore
@itemize
@item Prototype:

@example
grub_err_t
grub_video_restore (void);
@end example
@item Description:

Video subsystem will deinitialize activated video driver to restore old state of video device. This can be used to switch back to text mode.
@end itemize

@subsection grub_video_get_info
@itemize
@item Prototype:

@example
grub_err_t
grub_video_get_info (struct grub_video_mode_info *mode_info);
@end example
@example
struct grub_video_mode_info
@{
  /* Width of the screen.  */
  unsigned int width;
  /* Height of the screen.  */
  unsigned int height;
  /* Mode type bitmask.  Contains information like is it Index color or
     RGB mode.  */
  unsigned int mode_type;
  /* Bits per pixel.  */
  unsigned int bpp;
  /* Bytes per pixel.  */
  unsigned int bytes_per_pixel;
  /* Pitch of one scanline.  How many bytes there are for scanline.  */
  unsigned int pitch;
  /* In index color mode, number of colors.  In RGB mode this is 256.  */
  unsigned int number_of_colors;
  /* Optimization hint how binary data is coded.  */
  enum grub_video_blit_format blit_format;
  /* How many bits are reserved for red color.  */
  unsigned int red_mask_size;
  /* What is location of red color bits.  In Index Color mode, this is 0.  */
  unsigned int red_field_pos;
  /* How many bits are reserved for green color.  */
  unsigned int green_mask_size;
  /* What is location of green color bits.  In Index Color mode, this is 0.  */
  unsigned int green_field_pos;
  /* How many bits are reserved for blue color.  */
  unsigned int blue_mask_size;
  /* What is location of blue color bits.  In Index Color mode, this is 0.  */
  unsigned int blue_field_pos;
  /* How many bits are reserved in color.  */
  unsigned int reserved_mask_size;
  /* What is location of reserved color bits.  In Index Color mode,
     this is 0.  */
  unsigned int reserved_field_pos;
@};
@end example
@item Description:

Software developer can use this function to query properties of active rendering taget. Information provided here can be used by other parts of GRUB, like image loaders to convert loaded images to correct screen format to allow more optimized blitters to be used. If there there is no configured video driver with active screen, error @code{GRUB_ERR_BAD_DEVICE} is returned, otherwise @code{mode_info} is filled with valid information and @code{GRUB_ERR_NONE} is returned.
@end itemize

@subsection grub_video_get_blit_format
@itemize
@item Prototype:

@example
enum grub_video_blit_format
grub_video_get_blit_format (struct grub_video_mode_info *mode_info);
@end example
@example
enum grub_video_blit_format
  @{
    /* Follow exactly field & mask information.  */
    GRUB_VIDEO_BLIT_FORMAT_RGBA,
    /* Make optimization assumption.  */
    GRUB_VIDEO_BLIT_FORMAT_R8G8B8A8,
    /* Follow exactly field & mask information.  */
    GRUB_VIDEO_BLIT_FORMAT_RGB,
    /* Make optimization assumption.  */
    GRUB_VIDEO_BLIT_FORMAT_R8G8B8,
    /* When needed, decode color or just use value as is.  */
    GRUB_VIDEO_BLIT_FORMAT_INDEXCOLOR
  @};
@end example
@item Description:

Used to query how data could be optimized to suit specified video mode. Returns exact video format type, or a generic one if there is no definition for the type. For generic formats, use @code{grub_video_get_info} to query video color coding settings.
@end itemize

@subsection grub_video_set_palette
@itemize
@item Prototype:

@example
grub_err_t
grub_video_set_palette (unsigned int start, unsigned int count, struct grub_video_palette_data *palette_data);
@end example
@example
struct grub_video_palette_data
@{
    grub_uint8_t r; /* Red color value (0-255). */
    grub_uint8_t g; /* Green color value (0-255). */
    grub_uint8_t b; /* Blue color value (0-255). */
    grub_uint8_t a; /* Reserved bits value (0-255). */
@};
@end example
@item Description:

Used to setup indexed color palettes. If mode is RGB mode, colors will be set to emulated palette data. In Indexed Color modes, palettes will be set to hardware. Color values will be converted to suit requirements of the video mode. @code{start} will tell what hardware color index (or emulated color index) will be set to according information in first indice of @code{palette_data}, after that both hardware color index and @code{palette_data} index will be incremented until @code{count} number of colors have been set.
@end itemize

@subsection grub_video_get_palette
@itemize
@item Prototype:

@example
grub_err_t
grub_video_get_palette (unsigned int start, unsigned int count, struct grub_video_palette_data *palette_data);
@end example
@example
struct grub_video_palette_data
@{
    grub_uint8_t r; /* Red color value (0-255). */
    grub_uint8_t g; /* Green color value (0-255). */
    grub_uint8_t b; /* Blue color value (0-255). */
    grub_uint8_t a; /* Reserved bits value (0-255). */
@};
@end example
@item Description:

Used to query indexed color palettes. If mode is RGB mode, colors will be copied from emulated palette data. In Indexed Color modes, palettes will be read from hardware. Color values will be converted to suit structure format. @code{start} will tell what hardware color index (or emulated color index) will be used as a source for first indice of @code{palette_data}, after that both hardware color index and @code{palette_data} index will be incremented until @code{count} number of colors have been read.
@end itemize

@subsection grub_video_set_viewport
@itemize
@item Prototype:

@example
grub_err_t
grub_video_set_viewport (unsigned int x, unsigned int y, unsigned int width, unsigned int height);
@end example
@item Description:

Used to specify viewport where draw commands are performed. When viewport is set, all draw commands coordinates relate to those specified by @code{x} and @code{y}. If draw commands try to draw over viewport, they are clipped. If developer requests larger than possible viewport, width and height will be clamped to fit screen. If @code{x} and @code{y} are out of bounds, all functions drawing to screen will not be displayed. In order to maximize viewport, use @code{grub_video_get_info} to query actual screen dimensions and provide that information to this function.
@end itemize

@subsection grub_video_get_viewport
@itemize
@item Prototype:

@example
grub_err_t
grub_video_get_viewport (unsigned int *x, unsigned int *y, unsigned int *width, unsigned int *height);
@end example
@item Description:

Used to query current viewport dimensions. Software developer can use this to choose best way to render contents of the viewport.
@end itemize

@subsection grub_video_map_color
@itemize
@item Prototype:

@example
grub_video_color_t
grub_video_map_color (grub_uint32_t color_name);
@end example
@item Description:

Map color can be used to support color themes in GRUB. There will be collection of color names that can be used to query actual screen mapped color data. Examples could be @code{GRUB_COLOR_CONSOLE_BACKGROUND}, @code{GRUB_COLOR_CONSOLE_TEXT}. The actual color defines are not specified at this point.
@end itemize

@subsection grub_video_map_rgb
@itemize
@item Prototype:

@example
grub_video_color_t
grub_video_map_rgb (grub_uint8_t red, grub_uint8_t green, grub_uint8_t blue);
@end example
@item Description:

Map RGB values to compatible screen color data. Values are expected to be in range 0-255 and in RGB modes they will be converted to screen color data. In index color modes, index color palette will be searched for specified color and then index is returned.
@end itemize

@subsection grub_video_map_rgba
@itemize
@item Prototype:

@example
grub_video_color_t
grub_video_map_rgba (grub_uint8_t red, grub_uint8_t green, grub_uint8_t blue, grub_uint8_t alpha);
@end example
@item Description:

Map RGBA values to compatible screen color data. Values are expected to be in range 0-255. In RGBA modes they will be converted to screen color data. In index color modes, index color palette will be searched for best matching color and its index is returned.
@end itemize

@subsection grub_video_unmap_color
@itemize
@item Prototype:

@example
grub_err_t
grub_video_unmap_color (grub_video_color_t color, grub_uint8_t *red, grub_uint8_t *green, grub_uint8_t *blue, grub_uint8_t *alpha);
@end example
@item Description:

Unmap color value from @code{color} to color channels in @code{red}, @code{green}, @code{blue} and @code{alpha}. Values will be in range 0-255. Active rendering target will be used for color domain. In case alpha information is not available in rendering target, it is assumed to be opaque (having value 255).
@end itemize

@subsection grub_video_fill_rect
@itemize
@item Prototype:

@example
grub_err_t
grub_video_fill_rect (grub_video_color_t color, int x, int y, unsigned int width, unsigned int height);
@end example
@item Description:

Fill specified area limited by given coordinates within specified viewport. Negative coordinates are accepted in order to allow easy moving of rectangle within viewport. If coordinates are negative, area of the rectangle will be shrinken to follow size limits of the viewport.

Software developer should use either @code{grub_video_map_color}, @code{grub_video_map_rgb} or @code{grub_video_map_rgba} to map requested color to @code{color} parameter.
@end itemize

@subsection grub_video_blit_glyph
@itemize
@item Prototype:

@example
grub_err_t
grub_video_blit_glyph (struct grub_font_glyph *glyph, grub_video_color_t color, int x, int y);
@end example
@example
struct grub_font_glyph @{
    /* TBD. */
@};
@end example
@item Description:

Used to blit glyph to viewport in specified coodinates. If glyph is at edge of viewport, pixels outside of viewport will be clipped out. Software developer should use either @code{grub_video_map_rgb} or @code{grub_video_map_rgba} to map requested color to @code{color} parameter.
@end itemize

@subsection grub_video_blit_bitmap
@itemize
@item Prototype:

@example
grub_err_t
grub_video_blit_bitmap (struct grub_video_bitmap *bitmap, enum grub_video_blit_operators oper, int x, int y, int offset_x, int offset_y, unsigned int width, unsigned int height);
@end example
@example
struct grub_video_bitmap
@{
    /* TBD. */
@};

enum grub_video_blit_operators
  @{
    GRUB_VIDEO_BLIT_REPLACE,
    GRUB_VIDEO_BLIT_BLEND
  @};
@end example
@item Description:

Used to blit bitmap to viewport in specified coordinates. If part of bitmap is outside of viewport region, it will be clipped out. Offsets affect bitmap position where data will be copied from. Negative values for both viewport coordinates and bitmap offset coordinates are allowed. If data is looked out of bounds of bitmap, color value will be assumed to be transparent. If viewport coordinates are negative, area of the blitted rectangle will be shrinken to follow size limits of the viewport and bitmap. Blitting operator @code{oper} specifies should source pixel replace data in screen or blend with pixel alpha value.

Software developer should use @code{grub_video_bitmap_create} or @code{grub_video_bitmap_load} to create or load bitmap data.
@end itemize

@subsection grub_video_blit_render_target
@itemize
@item Prototype:

@example
grub_err_t
grub_video_blit_render_target (struct grub_video_render_target *source, enum grub_video_blit_operators oper, int x, int y, int offset_x, int offset_y, unsigned int width, unsigned int height);
@end example
@example
struct grub_video_render_target @{
    /* This is private data for video driver. Should not be accessed from elsewhere directly.  */
@};

enum grub_video_blit_operators
  @{
    GRUB_VIDEO_BLIT_REPLACE,
    GRUB_VIDEO_BLIT_BLEND
  @};
@end example
@item Description:

Used to blit source render target to viewport in specified coordinates. If part of source render target is outside of viewport region, it will be clipped out. If blitting operator is specified and source contains alpha values, resulting pixel color components will be calculated using formula ((src_color * src_alpha) + (dst_color * (255 - src_alpha)) / 255, if target buffer has alpha, it will be set to src_alpha. Offsets affect render target position where data will be copied from. If data is looked out of bounds of render target, color value will be assumed to be transparent. Blitting operator @code{oper} specifies should source pixel replace data in screen or blend with pixel alpha value.
@end itemize

@subsection grub_video_scroll
@itemize
@item Prototype:

@example
grub_err_t
grub_video_scroll (grub_video_color_t color, int dx, int dy);
@end example
@item Description:

Used to scroll viewport to specified direction. New areas are filled with specified color. This function is used when screen is scroller up in video terminal.
@end itemize

@subsection grub_video_swap_buffers
@itemize
@item Prototype:

@example
grub_err_t
grub_video_swap_buffers (void);
@end example
@item Description:

If double buffering is enabled, this swaps frontbuffer and backbuffer, in order to show values drawn to back buffer. Video driver is free to choose how this operation is techincally done.
@end itemize

@subsection grub_video_create_render_target
@itemize
@item Prototype:

@example
grub_err_t
grub_video_create_render_target (struct grub_video_render_target **result, unsigned int width, unsigned int height, unsigned int mode_type);
@end example
@example
struct grub_video_render_target @{
    /* This is private data for video driver. Should not be accessed from elsewhere directly.  */
@};
@end example
@item Description:

Driver will use information provided to it to create best fitting render target. @code{mode_type} will be used to guide on selecting what features are wanted for render target. Supported values for @code{mode_type} are @code{GRUB_VIDEO_MODE_TYPE_INDEX_COLOR} for index color modes, @code{GRUB_VIDEO_MODE_TYPE_RGB} for direct RGB color modes and @code{GRUB_VIDEO_MODE_TYPE_ALPHA} for alpha component.
@end itemize

@subsection grub_video_delete_render_target
@itemize
@item Prototype:

@example
grub_err_t
grub_video_delete_render_target (struct grub_video_render_target *target);
@end example
@item Description:

Used to delete previously created render target. If @code{target} contains @code{NULL} pointer, nothing will be done. If render target is correctly destroyed, GRUB_ERR_NONE is returned.
@end itemize

@subsection grub_video_set_active_render_target
@itemize
@item Prototype:

@example
grub_err_t
grub_video_set_active_render_target (struct grub_video_render_target *target);
@end example
@item Description:

Sets active render target. If this comand is successful all drawing commands will be done to specified @code{target}. There is also special values for target, @code{GRUB_VIDEO_RENDER_TARGET_DISPLAY} used to reference screen's front buffer, @code{GRUB_VIDEO_RENDER_TARGET_FRONT_BUFFER} used to reference screen's front buffer (alias for @code{GRUB_VIDEO_RENDER_TARGET_DISPLAY}) and @code{GRUB_VIDEO_RENDER_TARGET_BACK_BUFFER} used to reference back buffer (if double buffering is enabled). If render target is correclty switched GRUB_ERR_NONE is returned. In no any event shall there be non drawable active render target.

@end itemize
@subsection grub_video_get_active_render_target
@itemize
@item Prototype:

@example
grub_err_t
grub_video_get_active_render_target (struct grub_video_render_target **target);
@end example
@item Description:

Returns currently active render target. It returns value in @code{target} that can be subsequently issued back to @code{grub_video_set_active_render_target}.
@end itemize

@node Example usage of Video API
@section Example usage of Video API
@subsection Example of screen setup
@example
grub_err_t rc;
/* Try to initialize video mode 1024 x 768 with direct RGB.  */
rc = grub_video_setup (1024, 768, GRUB_VIDEO_MODE_TYPE_RGB);
if (rc != GRUB_ERR_NONE)
@{
  /* Fall back to standard VGA Index Color mode.  */
  rc = grub_video_setup (640, 480, GRUB_VIDEO_MODE_TYPE_INDEX);
  if (rc != GRUB_ERR_NONE)
  @{
  /* Handle error.  */
  @}
@}
@end example
@subsection Example of setting up console viewport
@example
grub_uint32_t x, y, width, height;
grub_video_color_t color;
struct grub_font_glyph glyph;
grub_err_t rc;
/* Query existing viewport.  */
grub_video_get_viewport (&x, &y, &width, &height);
/* Fill background.  */
color = grub_video_map_color (GRUB_COLOR_BACKGROUND);
grub_video_fill_rect (color, 0, 0, width, height);
/* Setup console viewport.  */
grub_video_set_viewport (x + 10, y + 10, width - 20, height - 20);
grub_video_get_viewport (&x, &y, &width, &height);
color = grub_video_map_color (GRUB_COLOR_CONSOLE_BACKGROUND);
grub_video_fill_rect (color, 0, 0, width, height);
/* Draw text to viewport.  */
color = grub_video_map_color (GRUB_COLOR_CONSOLE_TEXT);
grub_font_get_glyph ('X', &glyph);
grub_video_blit_glyph (&glyph, color, 0, 0);
@end example

@node Bitmap API
@section Bitmap API
@itemize
@subsection grub_video_bitmap_create
@item Prototype:
@example
grub_err_t grub_video_bitmap_create (struct grub_video_bitmap **bitmap, unsigned int width, unsigned int height, enum grub_video_blit_format blit_format)
@end example

@item Description:

Creates a new bitmap with given dimensions and blitting format. Allocated bitmap data can then be modified freely and finally blitted with @code{grub_video_blit_bitmap} to rendering target.
@end itemize

@subsection grub_video_bitmap_destroy
@itemize
@item Prototype:
@example
grub_err_t grub_video_bitmap_destroy (struct grub_video_bitmap *bitmap);
@end example

@item Description:

When bitmap is no longer needed, it can be freed from memory using this command. @code{bitmap} is previously allocated bitmap with @code{grub_video_bitmap_create} or loaded with @code{grub_video_bitmap_load}.
@end itemize

@subsection grub_video_bitmap_load
@itemize
@item Prototype:
@example
grub_err_t grub_video_bitmap_load (struct grub_video_bitmap **bitmap, const char *filename);
@end example

@item Description:

Tries to load given bitmap (@code{filename}) using registered bitmap loaders. In case bitmap format is not recognized or supported error @code{GRUB_ERR_BAD_FILE_TYPE} is returned.
@end itemize

@subsection grub_video_bitmap_get_width
@itemize
@item Prototype:
@example
unsigned int grub_video_bitmap_get_width (struct grub_video_bitmap *bitmap);
@end example

@item Description:

Returns bitmap width.
@end itemize

@subsection grub_video_bitmap_get_height
@itemize
@item Prototype:
@example
unsigned int grub_video_bitmap_get_height (struct grub_video_bitmap *bitmap);
@end example

@item Description:

Return bitmap height.
@end itemize

@subsection grub_video_bitmap_get_mode_info
@itemize
@item Prototype:
@example
void grub_video_bitmap_get_mode_info (struct grub_video_bitmap *bitmap, struct grub_video_mode_info *mode_info);
@end example

@item Description:

Returns bitmap format details in form of @code{grub_video_mode_info}.
@end itemize

@subsection grub_video_bitmap_get_data
@itemize
@item Prototype:
@example
void *grub_video_bitmap_get_data (struct grub_video_bitmap *bitmap);
@end example

@item Description:

Return pointer to bitmap data. Contents of the pointed data can be freely modified. There is no extra protection against going off the bounds so you have to be carefull how to access the data.
@end itemize

@node PFF2 Font File Format
@chapter PFF2 Font File Format

@c Author: Colin D. Bennett <colin@gibibit.com>
@c Date: 8 January 2009

@menu
* Introduction::
* File Structure::
* Font Metrics::
@end menu


@node Introduction
@section Introduction

The goal of this format is to provide a bitmap font format that is simple to
use, compact, and cleanly supports Unicode.


@subsection Goals of the GRUB Font Format

@itemize
@item Simple to read and use.
Since GRUB will only be reading the font files,
we are more concerned with making the code to read the font simple than we
are with writing the font.

@item Compact storage.
The fonts will generally be stored in a small boot
partition where GRUB is located, and this may be on a removable storage
device such as a CD or USB flash drive where space is more limited than it
is on most hard drives.

@item Unicode.
GRUB should not have to deal with multiple character
encodings.  The font should always use Unicode character codes for simple
internationalization.
@end itemize

@subsection Why Another Font Format?

There are many existing bitmap font formats that GRUB could use.  However,
there are aspects of these formats that may make them less than suitable for
use in GRUB at this time:

@table @samp
@item BDF 
Inefficient storage; uses ASCII to describe properties and 
hexadecimal numbers in ASCII for the bitmap rows.
@item PCF  
Many format variations such as byte order and bitmap padding (rows
padded to byte, word, etc.) would result in more complex code to
handle the font format.
@end table

@node File Structure
@section File Structure

A file @strong{section} consists of a 4-byte name, a 32-bit big-endian length (not
including the name or length), and then @var{length} more section-type-specific 
bytes.

The standard file extension for PFF2 font files is @file{.pf2}.


@subsection Section Types

@table @samp
@item FILE
@strong{File type ID} (ASCII string).  This must be the first section in the file.  It has length 4
and the contents are the four bytes of the ASCII string @samp{PFF2}.

@item NAME
@strong{Font name} (ASCII string).  This is the full font name including family,
weight, style, and point size.  For instance, "Helvetica Bold Italic 14".

@item FAMI
@strong{Font family name} (ASCII string).  For instance, "Helvetica".  This should
be included so that intelligent font substitution can take place.

@item WEIG
@strong{Font weight} (ASCII string).  Valid values are @samp{bold} and @samp{normal}.
This should be included so that intelligent font substitution can take
place.

@item SLAN
@strong{Font slant} (ASCII string).  Valid values are @samp{italic} and @samp{normal}.
This should be included so that intelligent font substitution can take
place.

@item PTSZ
@strong{Font point size} (uint16be).

@item MAXW
@strong{Maximum character width in pixels} (uint16be).

@item MAXH
@strong{Maximum character height in pixels} (uint16be).

@item ASCE
@strong{Ascent in pixels} (uint16be).  @xref{Font Metrics}, for details.

@item DESC
@strong{Descent in pixels} (uint16be).  @xref{Font Metrics}, for details.

@item CHIX
@strong{Character index.}
The character index begins with a 32-bit big-endian unsigned integer
indicating the total size of the section, not including this size value.
For each character, there is an instance of the following entry structure:

@itemize
@item @strong{Unicode code point.} (32-bit big-endian integer.)

@item @strong{Storage flags.} (byte.)
       
@itemize
@item Bits 2..0: 

If equal to 000 binary, then the character data is stored
uncompressed beginning at the offset indicated by the character's
@strong{offset} value.

If equal to 001 binary, then the character data is stored within a 
compressed character definition block that begins at the offset 
within the file indicated by the character's @strong{offset} value.
@end itemize

@item @strong{Offset.} (32-bit big-endian integer.)

A marker that indicates the remainder of the file is data accessed via
the character index (CHIX) section.  When reading this font file, the rest
of the file can be ignored when scanning the sections.  The length should
be set to -1 (0xFFFFFFFF).

Supported data structures:

Character definition
Each character definition consists of:

@itemize
@item @strong{Width.}
Width of the bitmap in pixels.  The bitmap's extents 
represent the glyph's bounding box.  @code{uint16be}.

@item @strong{Height.}
Height of the bitmap in pixels.  The bitmap's extents
represent the glyph's bounding box.  @code{uint16be}.

@item @strong{X offset.}
The number of pixels to shift the bitmap by
horizontally before drawing the character. @code{int16be}.

@item @strong{Y offset.}
The number of pixels to shift the bitmap by
vertically before drawing the character. @code{int16be}.

@item @strong{Device width.}
The number of pixels to advance horizontally from
this character's origin to the origin of the next character.
@code{int16be}.

@item @strong{Bitmap data.}
This is encoded as a string of bits.  It is
organized as a row-major, top-down, left-to-right bitmap.  The most
significant bit of each byte is taken to be the leftmost or uppermost
bit in the byte.  For the sake of compact storage, rows are not padded
to byte boundaries (i.e., a single byte may contain bits belonging to
multiple rows).  The last byte of the bitmap @strong{is} padded with zero
bits in the bits positions to the right of the last used bit if the
bitmap data does not fill the last byte.  
         
The length of the @strong{bitmap data} field is (@var{width} * @var{height} + 7) / 8
using integer arithmetic, which is equivalent to ceil(@var{width} *
@var{height} / 8) using real number arithmetic.

It remains to be determined whether bitmap fonts usually make all
glyph bitmaps the same height, or if smaller glyphs are stored with
bitmaps having a lesser height.  In the latter case, the baseline
would have to be used to calculate the location the bitmap should be
anchored at on screen.
@end itemize

@end itemize
@end table

@node Font Metrics
@section Font Metrics

@itemize
@item Ascent.
The distance from the baseline to the top of most characters.
Note that in some cases characters may extend above the ascent.

@item Descent.
The distance from the baseline to the bottom of most characters.  Note that
in some cases characters may extend below the descent.
 
@item Leading.
The amount of space, in pixels, to leave between the descent of one line of
text and the ascent of the next line.  This metrics is not specified in the
current file format; instead, the font rendering engine calculates a
reasonable leading value based on the other font metrics.

@item Horizonal leading.
The amount of space, in pixels, to leave horizontally between the left and
right edges of two adjacent glyphs.  The @strong{device width} field determines
the effective leading value that is used to render the font.

@end itemize
@image{font_char_metrics,,,,.png}
   
An illustration of how the various font metrics apply to characters.



@node Graphical Menu Software Design
@chapter Graphical Menu Software Design

@c By Colin D. Bennett <colin@gibibit.com>
@c Date: 17 August 2008

@menu
* Introduction_2::
* Startup Sequence::
* GUI Components::
* Command Line Window::
@end menu

@node Introduction_2
@section Introduction

The @samp{gfxmenu} module provides a graphical menu interface for GRUB 2.  It
functions as an alternative to the menu interface provided by the @samp{normal}
module, which uses the grub terminal interface to display a menu on a
character-oriented terminal.

The graphical menu uses the GRUB video API, which is currently for the VESA
BIOS extensions (VBE) 2.0+.  This is supported on the i386-pc platform.
However, the graphical menu itself does not depend on using VBE, so if another
GRUB video driver were implemented, the @samp{gfxmenu} graphical menu would work
on the new video driver as well.


@node Startup Sequence
@section Startup Sequence

@itemize
@item grub_enter_normal_mode [normal/main.c]
@item grub_normal_execute [normal/main.c]
@item read_config_file [normal/main.c]
@item (When @file{gfxmenu.mod} is loaded with @command{insmod}, it will call @code{grub_menu_viewer_register()} to register itself.)
@item GRUB_MOD_INIT (gfxmenu) [gfxmenu/gfxmenu.c]
@item grub_menu_viewer_register [kern/menu_viewer.c]
@item grub_menu_viewer_show_menu [kern/menu_viewer.c]
@item get_current_menu_viewer() [kern/menu_viewer.c]
@item show_menu() [gfxmenu/gfxmenu.c]
@item grub_gfxmenu_model_new [gfxmenu/model.c]
@item grub_gfxmenu_view_new [gfxmenu/view.c]
@item set_graphics_mode [gfxmenu/view.c]
@item grub_gfxmenu_view_load_theme [gfxmenu/theme_loader.c]
@end itemize


@node GUI Components
@section GUI Components

The graphical menu implements a GUI component system that supports a
container-based layout system.  Components can be added to containers, and
containers (which are a type of component) can then be added to other
containers, to form a tree of components.  Currently, the root component of
this tree is a @samp{canvas} component, which allows manual layout of its child
components.

Components (non-container):

@itemize
@item label
@item image
@item progress_bar
@item circular_progress
@item list (currently hard coded to be a boot menu list)
@end itemize

Containers:

@itemize
@item canvas
@item hbox
@item vbox
@end itemize

The GUI component instances are created by the theme loader in
@file{gfxmenu/theme_loader.c} when a theme is loaded.  Theme files specify
statements such as @samp{+vbox@{ +label @{ text="Hello" @} +label@{ text="World" @} @}}
to add components to the component tree root.  By nesting the component
creation statements in the theme file, the instantiated components are nested
the same way.

When a component is added to a container, that new child is considered @strong{owned}
by the container.  Great care should be taken if the caller retains a
reference to the child component, since it will be destroyed if its parent
container is destroyed.  A better choice instead of storing a pointer to the
child component is to use the component ID to find the desired component.
Component IDs do not have to be unique (it is often useful to have multiple
components with an ID of "__timeout__", for instance).

In order to access and use components in the component tree, there are two
functions (defined in @file{gfxmenu/gui_util.c}) that are particularly useful:

@itemize

@item @code{grub_gui_find_by_id (root, id, callback, userdata)}:

This function ecursively traverses the component tree rooted at @var{root}, and
for every component that has an ID equal to @var{id}, calls the function pointed
to by @var{callback} with the matching component and the void pointer @var{userdata}
as arguments.  The callback function can do whatever is desired to use the
component passed in.

@item @code{grub_gui_iterate_recursively (root, callback, userdata)}:

This function calls the function pointed to by @var{callback} for every
component that is a descendant of @var{root} in the component tree.  When the
callback function is called, the component and the void pointer @var{userdata}
as arguments.  The callback function can do whatever is desired to use the
component passed in.
@end itemize

@node Command Line Window
@section Command Line Window

The terminal window used to provide command line access within the graphical
menu is managed by @file{gfxmenu/view.c}.  The @samp{gfxterm} terminal is used, and
it has been modified to allow rendering to an offscreen render target to allow
it to be composed into the double buffering system that the graphical menu
view uses.  This is bad for performance, however, so it would probably be a
good idea to make it possible to temporarily disable double buffering as long
as the terminal window is visible.  There are still unresolved problems that
occur when commands are executed from the terminal window that change the
graphics mode.  It's possible that making @code{grub_video_restore()} return to
the graphics mode that was in use before @code{grub_video_setup()} was called
might fix some of the problems.


@node Copying This Manual
@appendix Copying This Manual

@menu
* GNU Free Documentation License::  License for copying this manual.
@end menu

@include fdl.texi


@node Index
@unnumbered Index

@c Currently, we use only the Concept Index.
@printindex cp

@bye