                                   Tux Paint
                                version 0.9.31

                      Magic Tool Plugin API Documentation

        Copyright © 2007-2023 by various contributors; see AUTHORS.txt.
                             https://tuxpaint.org/

                                 7月 17, 2023

+--------------------------------------------------+
|                Table of Contents                 |
|--------------------------------------------------|
|   * Prequisites                                  |
|   * Interfaces                                   |
|       + 'Magic' tool plugin functions            |
|           o Common arguments to plugin functions |
|           o Required Plugin Functions            |
|               # Plugin "housekeeping" functions  |
|               # Plugin event functions           |
|       + Tux Paint Functions and Data             |
|           o Pixel Manipulations                  |
|           o Helper Functions                     |
|           o Informational                        |
|           o Tux Paint System Calls               |
|           o Color Conversions                    |
|       + Helper Macros in "tp_magic_api.h"        |
|       + Constant Definitions in "tp_magic_api.h" |
|   * Compiling                                    |
|       + Linux and other Unix-like Platforms      |
|       + Windows                                  |
|       + macOS                                    |
|   * Installing                                   |
|       + Linux and other Unix-like Platforms      |
|       + Windows                                  |
|       + macOS                                    |
|   * Creating plugins with multiple effects       |
|   * Example Code                                 |
|   * Getting Help                                 |
|   * Glossary                                     |
+--------------------------------------------------+

Overview

Beginning with version 0.9.18, Tux Paint's 'Magic' tools were converted from
routines that lived within the application itself, to a set of 'plugins' that
are loaded when Tux Paint starts up.

This division allows more rapid development of 'Magic' tools, and allows
programmers to create and test new tools without needing to integrate them
within the main Tux Paint source code. (Users of more professional graphics
tools, such as GIMP, should be familiar with this plugin concept.)

Prerequisites

Tux Paint is written in the C programming language, and uses the Simple
DirectMedia Layer library ('libSDL', or simply 'SDL'; available from https://
www.libsdl.org/). Therefore, for the moment at least, one must understand the C
language and how to compile C-based programs. Familiarity with the SDL API is
highly recommended, but some basic SDL concepts will be covered in this
document.

Interfaces

Those who create 'Magic' tool plugins for Tux Paint must provide some
interfaces (C functions) that Tux Paint may invoke.

Tux Paint utilizes SDL's "SDL_LoadObject()" and "SDL_LoadFunction()" routines
to load plugins (shared objects files; e.g., ".so" files on Linux or ".dll"
files on Windows) and find the functions within.

In turn, Tux Paint provides a number of helper functions that the plugin may
(or sometimes is required to) use. This is exposed as a C structure (or
"struct") which contains pointers to functions and other data inside Tux Paint.
A pointer to this structure gets passed along to the plugin's functions as an
argument when Tux Paint invokes them.

Plugins should #include the C header file "tp_magic_api.h", which exposes the
'Magic' tool plugin API. Also, when you run the C compiler to build a plugin,
you should use the command-line tool "tp-magic-config" to get the appropriate
compiler flags (such as where the compiler can find the Tux Paint plugin header
file, as well as SDL's header files) for building a plugin. (See "Compiling",
below.)

The C header file and command-line tool mentioned above are included with Tux
Paint — or in some cases, as part of a "Tux Paint 'Magic' Tool Plugin
Development package".

'Magic' tool plugin functions

'Magic' tool plugins must contain the functions listed below. Note: To avoid
'namespace' collisions, each function's name must start with the shared
object's filename (e.g., "blur.so" or "blur.dll" would have functions whose
names begin with "blur_"). This includes private functions (ones not used by
Tux Paint directly), unless you declare those as 'static'.

Common arguments to plugin functions

Here is a description of arguments that many of your plugin's functions will
need to accept.

magic_api * api

    Pointer to a C structure containing pointers to Tux Paint functions and
    other data that the plugin can (and sometimes should) use. The contents of
    this struct are described below.

    Note: The magic_api struct is defined in the C header file
    "tp_magic_api.h", which you should include at the top of your plugin's C
    source file:

        #include "tp_magic_api.h"



int which
    An index the plugin should use to differentiate different 'Magic' tools, if
    the plugin provides more than one. (If not, "which" will always be 0.) See
    "Creating plugins with multiple effects", below.

SDL_Surface * snapshot
    A snapshot of the previous Tux Paint canvas, taken when the the mouse was
    first clicked to activate the current magic tool. If you don't continuously
    affect the image during one hold of the mouse button, you should base your
    effects off the contents of this canvas. (That is, read from "snapshot" and
    write to "canvas", below.)

SDL_Surface * canvas
    The current Tux Paint drawing canvas. Your magical effects should end up
    here!

SDL_Rect * update_rect
    A pointer to an SDL 'rectangle' structure that you use to tell Tux Paint
    what part of the canvas has been updated. If your effect affects a 32x32
    area centered around the mouse pointer, you would fill the SDL_Rect as
    follows:

        update_rect->x = x - 16;
        update_rect->y = y - 16;
        update_rect->w = 32;
        update_rect->h = 32;

    Or, if your effect changes the entire canvas (e.g., flips it upside-down),
    you'd fill it as follows:

        update_rect->x = 0;
        update_rect->y = 0;
        update_rect->w = canvas->w;
        update_rect->h = canvas->h;

    Note: "update_rect" is a C pointer (an "SDL_Rect *" rather than just an
    "SDL_Rect") because you need to fill in its contents. Since it is a
    pointer, you access its elements via "->" (arrow) rather than "." (dot).


Required Plugin Functions

Your plugin is required to contain, at the least, all of the following
functions.

Note: Remember, your plugin's function names must be preceded by your plugin's
filename. That is, if your plugin is called "zoom.so" (on Linux) or "zoom.dll"
(on Windows), then the names of your functions must begin with "zoom_" (e.g.,
"zoom_get_name(...)").

Plugin "housekeeping" functions

Uint32 api_version(void)

    The plugin should return an integer value representing the version of the
    Tux Paint 'Magic' tool plugin API the plugin was built against. The safest
    thing to do is return the value of TP_MAGIC_API_VERSION, which is defined
    in "tp_magic_api.h". If Tux Paint deems your plugin to be compatible, it
    will go ahead and use it.

    Note: Called once by Tux Paint, at startup. It is called first.



int init(magic_api * api, Uint32 disabled_features)

    The plugin should do any initialization here. Return '1' if initialization
    was successful, or '0' if not (and Tux Paint will not present any 'Magic'
    tools from the plugin).

    Note: Called once by Tux Paint, at startup. It is called after "api_version
    ()", if Tux Paint believes your plugin to be compatible.

    The disabled_features value contains bits set for any Tux Paint features
    relevant to Magic tools which have been disabled in this session. Test
    using the C bitwise 'and' operator, '&'. The features are defined in
    tp_magic_api.h:
      + MAGIC_FEATURE_CONTROL: Magic tool controls (paint vs fullscreen)
        (--nomagiccontrols)
      + MAGIC_FEATURE_SIZE: Magic tool size (--nomagicsizes)
    Your Magic tool(s) may wish to react differently depending on whether one
    or more features have been disabled. (For example, the "Brick" Magic tool
    always offered two tool variations: large and small. With the addition of
    the size feature, only one tool is necessary. However, with the size option
    disabled, the plugin is able to revert back to providing two separate
    tools.)

    Note: Changed most recently in Tux Paint 0.9.30; Magic API version
    0x00000008.



int get_tool_count(magic_api * api)

    This should return the number of Magic tools this plugin provides to Tux
    Paint.

    Note: Called once by Tux Paint, at startup. It is called after your "init()
    ", if it succeeded.

    Note: You may wish to resond differently, based on whether certain features
    have been disabled (e.g., 'paint' versus 'entire picture' controls, or
    'Magic sizes' controls).



int modes(magic_api * api, int which)

    This lets you tell Tux Paint what modes your tool can be used in; either as
    a tool the user can paint with, or a tool that affects the entire drawing
    at once.

    You must return a value that's some combination of one or more of available
    modes:
      + MODE_PAINT - freehand paint (click and drag)
      + MODE_FULLSCREEN - applies to full image with one click
      + MODE_PAINT_WITH_PREVIEW - freehand paint, with preview (click and drag)
      + MODE_ONECLICK - applies to an area around the mouse, with one click
    e.g., if your tool is only one that the user can paint with, return
    "MODE_PAINT". If the user can do both, return "MODE_PAINT |
    MODE_FULLSCREEN" to tell Tux Paint it can do both.

    Note: Called once for each Magic tool your plugin claims to contain (by
    your "get_tool_count()").

    Note: Added to Tux Paint 0.9.21; Magic API version 0x00000002.



char * get_name(magic_api * api, int which)

    This should return a string containing the name of a magic tool. This will
    appear on the button in the 'Magic' selector within Tux Paint.

    Tux Paint will free() the string upon exit, so you should wrap it in a C
    strdup() call.

    Note: Called once for each Magic tool your plugin claims to contain (by
    your "get_tool_count()").



int get_group(magic_api * api, int which)

    Use this to group tools together within sections of the 'Magic' selector. A
    number of groups are pre-defined within an enum found in "tp_magic_api.h":
      + MAGIC_TYPE_DISTORTS — Tools that distort the shape of the image, like
        Blur, Emboss, and Ripples
      + MAGIC_TYPE_COLOR_FILTERS — Tools that mostly affect the colors of the
        image without distortion, like Darken, Negative, and Tint
      + MAGIC_TYPE_PICTURE_WARPS — Tools that warp or move the entire picture,
        like Shift, Flip, and Waves
      + MAGIC_TYPE_PAINTING — Tools that generally paint new content at the
        cursor position, like Grass, Bricks, and Rails
      + MAGIC_TYPE_PATTERN_PAINTING — Tools that paint in multiple places at
        once, like Kaleidoscope and the Symmetry tools
      + MAGIC_TYPE_PICTURE_DECORATIONS — Tools that apply decorations to the
        entire picture, like Blinds and Checkboard
      + MAGIC_TYPE_ARTISTIC — Special-purpose artistic tools, like Flower, the
        String tools, and the Rainbow-arc-drawing tools.

    Note: Called once for each Magic tool your plugin claims to contain (by
    your "get_tool_count()").

    Note: Added to Tux Paint 0.9.27; Magic API version 0x00000005.



SDL_Surface * get_icon(magic_api * api, int which)

    This should return an SDL_Surface containing the icon representing the
    tool. (A greyscale image with alpha, no larger than 40x40.) This will
    appear on the button in the 'Magic' selector within Tux Paint.

    Tux Paint will free ("SDL_FreeSurface()") the surface upon exit.

    Note: Called once for each Magic tool your plugin claims to contain (by
    your "get_tool_count()").



char * get_description(magic_api * api, int which, int mode)

    This should return a string containing the description of how to use a
    particular magic tool. This will appear as a help tip, explained by Tux the
    Penguin, within Tux Paint.

    Tux Paint will free() the string upon exit, so you should wrap it in a C
    strdup() call.

    Note: For each Magic tool your plugin claims to contain (reported by your
    "get_tool_count()" function), this function will be called for each mode
    the tool claims to support (reported by your "modes()" function).

    In other words, if your plugin contains two tools, one which works in paint
    mode only, and the other that works in both paint mode and full-image mode,
    your plugin's "get_description()" will be called three times.



int requires_colors(magic_api * api, int which)

    Return a '1' if the 'Magic' tool accepts colors (the 'Colors' palette in
    Tux Paint will be available), or '0' if not.

    Note: Called once for each Magic tool your plugin claims to contain (by
    your "get_tool_count()").



Uint8 accepted_sizes(magic_api * api, int which, int mode)

    Return how many size variations the 'Magic' tool accepts, in the given mode
    (i.e., 'MODE_PAINT' or 'MODE_FULLSCREEN). Return a '0' if the 'Magic' tool
    should not offer sizing options. Returning '1' is the same as returning
    '0'.

    Note: For each Magic tool your plugin claims to contain (reported by your
    "get_tool_count()" function), this function will be called for each mode
    the tool claims to support (reported by your "modes()" function).

    Note: Added to Tux Paint 0.9.30; Magic API version 0x00000008.



Uint8 default_size(magic_api * api, int which, int mode)

    Return the default size the 'Magic' tool should start out with, in the
    given mode. This will be the default setting for the tool the first time it
    is used during a Tux Paint session. If Tux Paint is being invoked with the
    sizing option disabled, this will be the only size requested by Tux Paint.
    Return a number between '1' and the amount you returned in accepted_sizes
    ().

    Note: For each Magic tool your plugin claims to contain (reported by your
    "get_tool_count()" function), this function will be called for each mode
    the tool claims to support (reported by your "modes()" function).

    Note: Added to Tux Paint 0.9.30; Magic API version 0x00000008.



void shutdown(magic_api * api)

    The plugin should do any cleanup here. If you allocated any memory or used
    SDL_Mixer to load any sounds during init(), for example, you should free()
    the allocated memory and Mix_FreeChunk() the sounds here.

    Note: This function is called once, when Tux Paint exits.




Plugin event functions

void switchin(magic_api * api, int which, int mode, SDL_Surface * snapshot,
    SDL_Surface * canvas)
    void switchout(magic_api * api, int which, int mode, SDL_Surface *
    snapshot, SDL_Surface * canvas)

    switchin() is called whenever one of the plugin's Magic tools becomes
    active, and switchout() is called whenever one becomes inactive. This can
    be because the user just clicked a specific Magic tool (the current one is
    switched-out, and a new one is switched-in).

    It can also happen when user leaves/returns from the selection of "Magic"
    tools when doing some other activity (i.e., using a different tool, such as
    "Text" or "Brush", activating a momentary tool, such as "Undo" and "Redo",
    or returning from a dialog — possibly with a new picture when it switches
    back — such as "Open", "New" or "Quit"). In this case, the same Magic tool
    is first 'switched-out', and then 'switched-back-in', usually moments
    later.

    Finally, it can also happen when the user changes the 'mode' of a tool
    (i.e., from paint mode to full-image mode). First switchout() is called for
    the old mode, then switchin() is called for the new mode.

    These functions allow users to interact in complicated was with Magic tools
    (for example, a tool that lets the user draw multiple freehand strokes, and
    then uses that as input such as handwriting — normally, the user could
    click somewhere in the canvas to tell the Magic tool they are 'finished',
    but if they switch to another tool, the Magic tool may want to undo any
    temporary changes to the canvas).

    These functions could also be used to streamline certain effects; a
    behind-the-scenes copy of the entire canvas could be altered in some way
    when the user first switches to the canvas, and then pieces of that copy
    could be drawn on the canvas when they draw with the Magic tool.

    Note: Added to Tux Paint 0.9.21; Magic API version 0x00000002.



void set_color(magic_api * api, int which, SDL_Surface * canvas, SDL_Surface *
    last, Uint8 r, Uint8 g, Uint8 b, SDL_Rect * update_rect)

    Tux Paint will call this function to inform the plugin of the RGB values of
    the currently-selected color in Tux Paint's 'Colors' palette. (It will be
    called whenever one of the plugin's Magic tools that accept colors becomes
    active, and whenever the user picks a new color while such a tool is
    currently active.)

    Generally, Magic tools will not alter the canvas in any way when receiving
    an updated color, but it is possible. (For example, the "Zoom" and
    "Perspective" tools apply effects which uses the current color choice as a
    solid background. The effects may be adjusted with subsequent click/drag
    operations, but you may also adjust the background color, without altering
    the zoom level or perspective, by simply picking a new color.)

    Note: Changed most recently in Tux Paint 0.9.29; Magic API version
    0x00000007.



void set_size(magic_api * api, int which, int mode, SDL_Surface * canvas,
    SDL_Surface * last, Uint8 size, SDL_Rect * update_rect)

    Tux Paint will call this function to inform the plugin of the 'Magic' tool
    size option chosen. (It will be called whenever one of the plugin's Magic
    tools that accept sizes becomes active, and whenever the user picks a new
    size while such a tool is currently active.)

    Generally, Magic tools will not alter the canvas in any way when receiving
    an updated size, but it is possible.

    Note: Added to Tux Paint 0.9.30; Magic API version 0x00000008.



void click(magic_api * api, int which, int mode, SDL_Surface * snapshot,
    SDL_Surface * canvas, int x, int y, SDL_Rect * update_rect)

    The plugin should apply the appropriate 'Magic' tool on the 'canvas'
    surface. The (x,y) coordinates are where the mouse was (within the canvas)
    when the mouse button was clicked, and you are told which 'mode' your tool
    is in (i.e., 'MODE_PAINT' or 'MODE_FULLSCREEN).

    The plugin should report back what part of the canvas was affected, by
    filling in the (x,y) and (w,h) elements of 'update_rect'.

    The contents of the drawing canvas immediately prior to the mouse button
    click is stored within the 'snapshot' canvas.



void drag(magic_api * api, int which, SDL_Surface * snapshot, SDL_Surface *
    canvas, int ox, int oy, int x, int y, SDL_Rect * update_rect)

    The plugin should apply the appropriate 'Magic' tool on the 'canvas'
    surface. The (ox,oy) and (x,y) coordinates are the location of the mouse at
    the beginning and end of the stroke.

    Typically, plugins that let the user "draw" effects onto the canvas utilize
    Tux Paint's "line()" 'Magic' tool plugin helper function to calculate the
    points of the line between (ox,oy) and (x,y), and call another function
    within the plugin to apply the effect at each point. (See "Tux Paint
    Functions and Data," below).

    The plugin should report back what part of the canvas was affected, by
    filling in the (x,y) and (w,h) elements of 'update_rect'.

    Note: The contents of the drawing canvas immediately prior to the mouse
    button click remains as it was (when the plugin's "click()" function was
    called), and is still available in the 'snapshot' canvas.



void release(magic_api * api, int which, SDL_Surface * snapshot, SDL_Surface *
    canvas, int x, int y, SDL_Rect * update_rect)

    The plugin should apply the appropriate 'Magic' tool on the 'canvas'
    surface. The (x,y) coordinates are where the mouse was (within the canvas)
    when the mouse button was released.

    The plugin should report back what part of the canvas was affected, by
    filling in the (x,y) and (w,h) elements of 'update_rect'.

    Note: The contents of the drawing canvas immediately prior to the mouse
    button click remains as it was (when the plugin's "click()" function was
    called), and is still available in the 'snapshot' canvas.




Tux Paint Functions and Data

Tux Paint provides a number of helper functions that plugins may access via the
"magic_api" structure, sent to all of the plugin's functions. (See "Required
Plugin Functions," above.)

Pixel Manipulations

Uint32 getpixel(SDL_Surface * surf, int x, int y)
    Retreives the pixel value from the (x,y) coordinates of an SDL_Surface.
    (You can use SDL's "SDL_GetRGB()" function to convert the Uint32 'pixel' to
    a set of Uint8 RGB values.)

void putpixel(SDL_Surface * surf, int x, int y, Uint32 pixel)
    Sets the pixel value at position (x,y) of an SDL_Surface. (You can use
    SDL's "SDL_MapRGB()" function to convert a set of Uint8 RGB values to a
    Uint32 'pixel' value appropriate to the destination surface.)

Uint32 xorpixel(SDL_Surface * surf, int x, int y)
    Applies an XOR (exclusive-or) operation to the pixel at coordinates (x,y)
    of the SDL_Surface. Applying an XOR again at the same position will return
    the pixel to the original value. Useful for displaying temporary
    'rubberband' lines, outlines, and crosshairs, while utilizing a Magic Tool.
SDL_Surface * scale(SDL_Surface * surf, int w, int h, int keep_aspect)

    This accepts an existing SDL surface and creates a new one scaled to an
    arbitrary size. (The original surface remains untouched.)

    The "keep_aspect" flag can be set to '1' to force the new surface to stay
    the same shape (aspect ratio) as the original, meaning it may not be the
    same width and height you requested. (Check the "->w" and "->h" elements of
    the output "SDL_Surface *" to determine the actual size.)


Helper Functions

int in_circle(int x, int y, int radius)
    Returns '1' if the (x,y) location is within a circle of a particular radius
    (centered around the origin: (0,0)). Returns '0' otherwise. Useful to
    create 'Magic' tools that affect the canvas with a circular brush shape.

void line(void * api, int which, SDL_Surface * canvas, SDL_Surface * snapshot,
    int x1, int y1, int x2, int y2, int step, FUNC callback)

    This function calculates all points on a line between the coordinates
    (x1,y1) and (x2,y2). Every 'step' iterations, it calls the 'callback'
    function.

    It sends the 'callback' function the (x,y) coordinates on the line, Tux
    Paint's "magic_api" struct (as a "void *" pointer which you need to send to
    it), a 'which' value, represening which of the plugin's 'Magic' tool is
    being used, and the current and snapshot canvases.

    Example prototype of a callback function that may be sent to Tux Paint's
    "line()" 'Magic' tool plugin helper function:

        void exampleCallBack(void * ptr_to_api, int which_tool, SDL_Surface *
        canvas, SDL_Surface * snapshot, int x, int y);

    Example use of the "line()" helper (e.g., within a plugin's draw()
    function):

        api->line((void *) api, which, canvas, snapshot, ox, oy, x, y, 1,
        exampleCallBack);



Uint8 touched(int x, int y)

    This function allows you to avoid re-processing the same pixels multiple
    times when the user drags the mouse across an area of the canvas, thus
    increasing Tux Paint's response time, especially with math-heavy effects.

    If your effect's "click()", "drag()" and/or "release()" functions take the
    contents of the source surface ("snapshot") and always create the same
    results in the desintation surface ("canvas"), you should wrap the effect
    in a call to "api->touched()".

    This function simply returns whether or not it had already been called for
    the same (x,y) coordinates, since the user first clicked the mouse. In
    other words, the first time you call it for a particular (x,y) coordinate,
    it returns '0'. Future calls will return '1' until the user releases the
    mouse button.

    Note: Magic effects that continuously affect the destination surface
    ("canvas") (ignoring the "snapshot surface) have no reason to use this
    function. The "Blur" and "Smudge" tools that ship with Tux Paint are
    examples of such effects.




Informational

char * tp_version
    A string containing the version of Tux Paint that's running (e.g.,
    "0.9.31").

int canvas_w
    int canvas_h
    Returns the width (canvas_w) and height (canvas_h) of the drawing canvas
    (in pixels).

int button_down(void)
    A '1' is returned if the mouse button is down; '0' otherwise.

char * data_directory

    This string contains the directory where Tux Paint's data files are stored.
    For example, on Linux, this may be "/usr/share/tuxpaint/".

    Magic tools should include an icon (see "get_icon()", above) and are
    encouraged to include sound effects, it's useful for plugins to know where
    such things are located.

    When compiling and installing a plugin, the "tp-magic-config" command-line
    tool should be used to determine where such data should be placed for the
    installed version of Tux Paint to find them. (See "Installing," below.)

    Note: If your plugin is installed locally (e.g., in your "~/.tuxpaint/
    plugins/" directory), rather than globally (system-wide), the
    "data_directory" value will be different. (e.g., "/home/username/.tuxpaint/
    plugins/data/").




Tux Paint System Calls

void update_progress_bar(void)
    Asks Tux Paint to animate and draw one frame of its progress bar (at the
    bottom of the screen). Useful for routines that may take a long time, to
    provide feedback to the user that Tux Paint has not crashed or frozen.

void playsound(Mix_Chunk * snd, int pan, int dist)

    This function plays a sound (one loaded by the SDL helper library
    "SDL_mixer"). It uses SDL_mixer's "Mix_SetPanning()" to set the volume of
    the sound on the left and right speakers, based on the 'pan' and 'dist'
    values sent to it.

    A 'pan' of 128 causes the sound to be played at equal volume on the left
    and right speakers. A 'pan' of 0 causes it to be played completely on the
    left, and 255 completely on the right.

    The 'dist' value affects overall volume. 255 is loudest, and 0 is silent.

    The 'pan' and 'dist' values can be used to simulate location and distance
    of the 'Magic' tool effect.



void stopsound(void)
    This function stops playing a sound played by playsound(). It is useful to
    silence effects when the user stops using the tool (in your 'release'
    function).

void special_notify(int flag)
    This function notifies Tux Paint of special events. Various values defined
    in "tp_magic_api.h" can be 'or'ed together (using C's boolean 'or': "|")
    and sent to this function.

    SPECIAL_FLIP

        The contents of the canvas has been flipped vertically.

        If a 'Starter' image was used as the basis of this image, it should be
        flipped too, and a record of the flip should be stored as part of Tux
        Paint's undo buffer stack. Additionally, the fact that the starter has
        been flipped (or unflipped) should be recorded on disk when the current
        drawing is saved.



    SPECIAL_MIRROR
        Similar to SPECIAL_FLIP, but for magic tools that mirror the contents
        of the canvas horizontally.





Color Conversions

float sRGB_to_linear(Uint8 srbg)
    Converts an 8-bit sRGB value (one between 0 and 255) to a linear floating
    point value (between 0.0 and 1.0).

uint8 linear_to_sRGB(float linear)
    Converts a linear floating point value (one between 0.0 and 1.0) to an
    8-bit sRGB value (between 0 and 255).

void rgbtohsv(Uint8 r, Uint8 g, Uint8 b, float * h, float * s, float * v)
    Converts 8-bit sRGB values (between 0 and 255) to floating-point HSV (Hue,
    Saturation and Value) values (Hue between 0.0 and 360.0, and Saturation and
    Value between 0.0 and 1.0).

void hsvtorgb(float h, float s, float v, Uint8 * r, Uint8 * g, Uint8 * b)
    Converts floating-point HSV (Hue, Saturation and Value) values (Hue between
    0.0 and 360.0, and Saturation and Value between 0.0 and 1.0) to 8-bit sRGB
    values (between 0 and 255).


For more information, refer to the sRGB article at Wikipedia and the HSV Color
Space article at Wikipedia.

Helper Macros in "tp_magic_api.h"

Along with the "magic_api" C structure containing functions and data described
above, the tp_magic_api.h C header file also contains some helper macros that
you may use.

min(x, y)
    max(x, y)
    The minimum (min) or maxinum (max) of 'x' and 'y'. For example, min() will
    return the value of 'x' if it is less than or equal to 'y', otherwise it
    will return 'y'.

clamp(lo, value, hi)

    A value, clamped to be no smaller than 'lo', and no higher than 'hi'. (That
    is, if 'value' is less than 'lo', then 'lo' will be used; if 'value' is
    greater than 'hi', then 'hi' will be used; otherwise, 'value' will be
    used.)

    Example: red = clamp(0, n, 255); will set the variable 'red' to be the
    value of the variable 'n', but without allowing it to become less than 0 or
    greater than 255.

    Note: This macro is simply a #define of: "(min(max(value,lo),hi))".




Constant Defintions in "tp_magic_api.h"

The following is a summary of constant values that are set (via "#define")
within the 'Magic' tool API header file.

TP_MAGIC_API_VERSION

    This integer value represents which version of the Tux Paint 'Magic' tool
    API the header corresponds to.

    It should be referenced by your magic tool's "api_version()" function, to
    inform the running copy of Tux Paint whether or not your plugin is
    compatible.

    Note: This version number does not correspond to Tux Paint's own release
    number (e.g., "0.9.31"). The API will not change every time a new version
    of Tux Paint is released, which means plugins compiled for earlier versions
    of Tux Paint will often run under newer versions.



SPECIAL_MIRROR
    SPECIAL_FLIP
    These are flags for Tux Paint's "special_notify()" helper function. They
    are described above.


Compiling

Linux and other Unix-like Platforms

Use the C compiler's "-shared" command-line option to generate a shared object
file (".so") based on your 'Magic' tool plugin's C source code.

Use the "tp-magic-config --cflags" command, supplied as part of Tux Paint — or
in some cases, as part of a "Tux Paint 'Magic' Tool Plugin Development package"
— to provide additional command-line flags to your C compiler that will help it
build your plugin.

Command-Line Example

As a stand-alone command, using the GNU C Compiler and BASH shell, for example:


    $ gcc -shared -fpic `tp-magic-config --cflags` my_plugin.c -o my_plugin.so

Note: The characters around the "tp-magic-config" command are a grave/backtick/
backquote ("`"), and not an apostrophe/single-quote ("'"). They tell the shell
to execute the command within (in this case, "tp-magic-config ..."), and use
its output as an argument to the command being executed (in this case, "gcc
...").

Makefile Example

A snippet from a Makefile to compile a Tux Paint "Magic" tool plugin might look
like this:

    CFLAGS=-Wall -O2 $(shell tp-magic-config --cflags)

    my_plugin.so: my_plugin.c
        gcc -shared $(CFLAGS) -o my_plugin.so my_plugin.c

The first line sets up Makefile variable ("CFLAGS") that contains flags for the
compiler. "-Wall" asks for all compiler warnings to be shown. "-O2" asks for
level 2 optimization. "($shell tp-magic-config --cflags)" runs
"tp-magic-config" to retrieve additional compiler flags that "Magic" tool
plugins require. (The "$(shell ...)" directive is similar to the ` ("grave")
character in the BASH shell examples, above.)

The next line defines a Makefile target, "my_plugin.so", and states that it
depends on the C source file "my_plugin.c". (Any time the C file changes,
"make" will know to recompile it and produce an updated ".so" file. If the C
file hadn't changed, it won't bother recompiling.)

The last line defines the command "make" should run when it determines that it
needs to (re)compile the ".so" file. Here, we're using "gcc", with "-shared and
"$(CFLAGS)" command-line arguments, like above. "-o my_plugin.so" tells the C
compiler that the output file should be "my_plugin.so". The last argument is
the C file to compile, in this case "my_plugin.c".

Note: Commands listed below a Makefile target should be intented using a single
tab character.

Advanced Makefile

An even more generalized Makefile might look like this:

    CFLAGS=-Wall -O2 $(shell tp-magic-config --cflags)

    my_plugin_1.so: my_plugin_1.c
        $(CC) -shared $(CFLAGS) -o $@ $<

    my_plugin_2.so: my_plugin_2.c
        $(CC) -shared $(CFLAGS) -o $@ $<

As before, there are lines that define the command "make" should run when it
determines that it needs to (re)compile the ".so" file(s). However, more
general terms are used...

"$(CC)" gets expanded to your default C compiler (e.g., "gcc"). "-shared" and
"$(CFLAGS)" are command-line arguments to the compiler, like above. "-o $@"
tells the C compiler what the output file should be; "make" replaces "$@" with
the name of the target, in this case "my_plugin_1.so" or "my_plugin_2.so". And
finally, the last argument is the C file to compile; "make" replaces "$<" with
the target's dependency, in this case "my_plugin_1.c" or "my_plugin_2.c".

Windows

TBD

macOS

TBD

Installing

Linux and other Unix-like Platforms

Use the "tp-magic-config" command-line tool, supplied as part of Tux Paint — or
in some cases, as part of a "Tux Paint 'Magic' Tool Plugin Development package"
— to determine where your plugins' files should go.

Shared Object

Use "tp-magic-config --pluginprefix" to determine where the plugin shared
object (".so") files should be installed. The value returned by this command
will be the global location where the installed copy of Tux Paint looks for
plugins (e.g., "/usr/lib/tuxpaint/plugins").

Alternatively, you may use "tp-magic-config --localpluginprefix" to find out
where Tux Paint expects to find local plugins for the current user (e.g., "/
home/username/.tuxpaint/plugins").

As stand-alone commands, using the BASH shell, for example:

    # cp my_plugin.so `tp-magic-config --pluginprefix`
    # chmod 644 `tp-magic-config --pluginprefix`/my_plugin.so

Note: See the note above regarding the "`" (grave) character.

Documentation

Use the "tp-magic-config --plugindocprefix" command to determine where
documentation for your "Magic" tools should go. The value returned by this
command will be the location where the documentation to the installed copy of
Tux Paint is stored. The main documentation includes a link to a folder where
"Magic" tools' documentation is expected to be installed

(e.g., "/usr/share/doc/tuxpaint/magic-docs").

Note: It's best to include both HTML and plain-text versions of your
documentation. An "html" subdirectory exists within the "magic-docs" directory,
and is where the HTML versions should go.

As stand-alone commands, using the BASH shell, for example:

    # cp my_plugin.html `tp-magic-config --plugindocprefix`/html
    # cp my_plugin.txt `tp-magic-config --plugindocprefix`

Note: See the note above regarding the "`" (grave) character.

Note: Currently, there is no "--localplugindocprefix" option.

Icons, Sounds and other Data Files

Use the "tp-magic-config --dataprefix" command, supplied as part of Tux Paint,
to determine where data files (PNG icon, Ogg Vorbis sound effects, etc.) should
be installed. The value returned by this command will be the same as the value
of the "data_directory" string stored within the "magic_api" structure that
your plugin's functions receive (e.g., "/usr/share/tuxpaint/").

For locally-installed plugins (for the current user only), use "tp-magic-config
--localdataprefix". It will return the value of "data_directory" string that
locally-installed plugins will see within their "magic_api" structure (e.g., "/
home/username/.tuxpaint/plugins/data/").

Note: Tux Paint's default Magic tool plugins install their data within "magic"
subdirectories of Tux Paint's "images" and "sounds" data directories (e.g., "/
usr/share/tuxpaint/images/magic/"). You are encouraged to do the same.

As stand-alone commands, using the BASH shell, for example:

    # cp my_plugin_icon.png `tp-magic-config --dataprefix`/images/magic/
    # chmod 644 `tp-magic-config --dataprefix`/images/magic/my_plugin_icon.png

Note: See the note above regarding the "`" (grave) character.

Putting it Together in a Makefile

A snippet from a more generalized Makefile might look like this:

    PLUGINPREFIX=$(shell tp-magic-config --pluginprefix)
    PLUGINDOCPREFIX=$(shell tp-magic-config --plugindocprefix)
    DATAPREFIX=$(shell tp-magic-config --dataprefix)

    install:
        #
        # Install plugin
        mkdir -p $(PLUGINPREFIX)
        cp *.so $(PLUGINPREFIX)/
        chmod 644 $(PLUGINPREFIX)/*.so
        #
        # Install icons
        mkdir -p $(DATAPREFIX)/images/magic
        cp icons/*.png $(DATAPREFIX)/images/magic/
        chmod 644 $(DATAPREFIX)/images/magic/*.png
        #
        # Install sound effects
        mkdir -p $(DATAPREFIX)/sounds/magic
        cp sounds/*.ogg $(DATAPREFIX)/sounds/magic/
        chmod 644 $(DATAPREFIX)/sounds/magic/*.ogg
        #
        # Install docs
        mkdir -p $(PLUGINDOCPREFIX)/html
        cp docs/*.html $(PLUGINDOCPREFIX)/html/
        cp docs/*.txt $(PLUGINDOCPREFIX)/
        chmod 644 $(PLUGINDOCPREFIX)/html/*.html
        chmod 644 $(PLUGINDOCPREFIX)/*.txt

The first three lines set up Makefile variables that contain the paths returned
by the "tp-magic-config" command-line tool. (The "$(shell ...)" directive is
similar to the ` ("grave") character in the BASH shell examples, above.)

Below that is an "install" target in the Makefile. (Invoked by, for example, "$
sudo make install" or "# make install".)

The "install" target uses "mkdir -p" to make sure that the plugin directory
exists, then uses "cp" to copy all plugin (".so") files into it, and invokes
"chmod" to make sure they are readable.

It then does a similar series of commands to install icon files (".png" images)
and sound effects (".ogg" files) into subdirectories within Tux Paint's data
directory, and to install documentation (".html" and ".txt" files) within Tux
Paint's documentation directory.

Note: The above Makefile example assumes the user will have priveleges to
install Tux Paint plugins system-wide.

Windows

TBD

macOS

TBD

Creating plugins with multiple effects

Plugins for Tux Paint may contain more than one effect. If you have multiple
effects that are similar, it may make sense to place them in one plugin file,
to reduce overhead and share code.

These following suggestions can help you create plugins that contain multiple
effects:

  * Use a C "enum" to enumerate the effects, and count them.

        enum {
            ONE_TOOL,
            ANOTHER_TOOL,
            AND_YET_ANOTHER_TOOL,
            NUM_TOOLS };

  * Return the value of "NUM_TOOLS" when "get_tool_count()" is called, and
    compare "which" values sent to other functions with the other enumerated
    values.
  * Create arrays of "NUM_TOOLS" length to contain effect-specific data.

        char * my_plugin_snd_filenames[NUM_TOOLS] = {
            "one.ogg", "another.ogg", "yet_another.ogg" };
        Mix_Chunk * my_plugin_snds[NUM_TOOLS]");

  * Use a C "for"-loop to load or create the effect-specific data (such as
    loading sound effects during your "init()").

        int i;
        char fname[1024];

        for (i = 0; i < NUM_TOOLS; i++)
        {
            /* Becomes, for example, "/usr/share/tuxpaint/sounds/magic/one.ogg"
        */

            snprintf(fname, sizeof(fname), "%s/sounds/magic/%s",
                api->data_prefix, my_plugin_snd_filenames[i]);

            my_plugin_snds[i] = Mix_LoadWAV(fname);
        }

  * Similarly, do the same to free them later (such as freeing sound effects
    during your "shutdown()").

            int i;

            for (i = 0; i < NUM_TOOLS; i++)
                Mix_FreeChunk(my_plugin_snds[i]);

  * Use "which" values sent to your functions as an index into those arrays
    (e.g., for playing the appropriate sound effect for a tool).

Note: Even if your plugin currently contains only one effect, it may be useful
to follow the steps above so that you can add a new variation of an effect with
little effort. ("NUM_TOOLS" will simply be '1', your arrays will be of length
'1', etc.)

Example Code

The C source file "tp_magic_example.c" contains a complete example of a plugin
with multiple simple effects.

Getting Help

For more information, check the Tux Paint website: https://tuxpaint.org/, and
the Simple DirectMedia Layer library website: http://www.libsdl.org/.

Additionally, other Tux Paint developers and users can be found on the
"tuxpaint-devel" and "tuxpaint-users" mailing lists: https://tuxpaint.org/lists
/.

Glossary

  * alpha: See "RGBA"
  * &: See "ampersand"
  * ampersand (pointers): "&". A symbol in C that allows you to refer to the
    memory address of a variable; that is, a pointer. (For example, consider
    "int i;". Later, "&i" refers to the memory where "i" is stored, not the
    value of "i" itself; it is a 'pointer to "i"'.) See also: "star"
  * ampersand (bitwise operator): "&". A symbol in C that acts as a bitwise
    "and" operator. Only bits set in both values will be returned. For example,
    "11 & 6" compares the binary values '1011' to '0110'. Only the bit in the
    2's place is set, so the result is 2 ('0010'). See also: "bit"
  * API: Application Programming Interface. TBD
  * argument: A value sent to a function.
  * arrow: "->". A symbol in C that references an element within a pointer to a
    struct.
  * backquote: See "grave"
  * backtick: See "grave"
  * bit: "Binary digit." Bits are the basic storage unit in a computer's
    memory, disk, networking, etc. They represent either 0 or 1. (Compared to a
    decimal digit, which can be anything between 0 and 9.) Just as a series of
    decimal digits can represent a larger number (e.g., "1" and "5" is fifteen
    (15)), so can bits (e.g., "1" and "0", is two). In decimal, we go from
    right to left: ones place, tens place, hundreds place, thousands place,
    etc. In binary, it is: ones place, twos place, fours place, eights place,
    etc. See also: "byte"
  * blue: See "RGBA"
  * boolean 'or': A mathematical operation that results in a true value if
    either operand is true. ("1 | 0", "0 | 1" and "1 | 1" all result in "1". "0
    | 0" results in "0".)
  * |: See "boolean 'or'"
  * .: See "dot"
  * `: See "grave"
  * *: See "star"
  * byte: A unit of memory made up of 8 bits. As a signed value, it can
    represent -128 through 127. As an unsigned value, it can represent 0
    through 255. As a series of bits, for example, the byte "00001100"
    represents the decimal value 12.
  * callback: TBD
  * C enumeration: A construct in C that allows you to label numeric values
    (usually starting at 0 and incrementing by one). (e.g., "enum { ONE, TWO,
    THREE };"
  * C function: TBD
  * C function prototype: TBD
  * C header file: TBD
  * channel: TBD
  * click: The action of pressing a button on a mouse.
  * coordinates: A set of numbers corresponding to a physical position; for
    example, in a two-dimensional (2D) image, "X" and "Y" coordinates specify
    the position across (left-to-right) and down the image, respectively. In
    SDL, the coordinates (0,0) is the top-leftmost pixel of a surface.
  * C pointer: A variable that contains the location of a piece of memory;
    usually used to 'point' to another variable. Since C functions can only
    return one value as a result, pointers are often sent to functions to allow
    the function to change the values of multiple variables. (For example, Tux
    Paint's "rgbtohsv()" and "hsvtorgb()".)
  * C structure: A construct in C that allows you to declare a new variable
    'type' which may contain other types within. For example, SDL's "SDL_Rect"
    contains four integer values, the coordinates of the rectangle (X,Y), and
    its dimensions (width and height).
  * #define: A C statement that defines a substitution that can occur later in
    the code. Generally used for constant values (e.g., "#define RADIUS 16";
    all instances of "RADIUS" will be replaced with "16"), but can also be used
    to create macros. Typically placed within C header files.
  * dimensions: The size of an object, in terms of its width (left to right)
    and height (top to bottom).
  * .dll: See "Shared Object"
  * dot: ".". A symbol in C that references an element within a struct.
  * drag: The action of moving a mouse while the button remains held.
  * element: A variable stored within a C structure. (Example: "w" and "h"
    elements of SDL_Surface store the surface's width and height,
    respectively.)
  * enum: See "C enumeration"
  * float: See "floating point"
  * floating point: TBD
  * format: An SDL_Surface element (a pointer to an SDL_PixelFormat structure)
    that contains information about a surface; for example, the number of bits
    used to represent each pixel). See also the "SDL_PixelFormat(3)" man page)
  * free(): A C function that frees (deallocates) memory allocated by other C
    functions (such as "strdup()").
  * function: See "C function"
  * gcc: The GNU C compiler, a portable Open Source compiler. See also the "gcc
    (1)" man page)
  * GIMP: An Open Source image manipulation and paint program.
  * GNU C Compiler: See "gcc"
  * grave: The "`" character; used by the BASH shell to use the output of a
    command as the command-line arguments to another.
  * green: See "RGBA"
  * ->: See "arrow"
  * .h: See "C header file"
  * header: See "C header file"
  * header file: See "C header file"
  * HSV: Hue, Saturation and Value. TBD
  * hue: See "HSV"
  * IMG_Load(): An SDL_image function that loads an image file (e.g., a PNG)
    and returns it as an "SDL_Surface *".
  * #include: A C statement that asks the compiler to read the contents of
    another file (usually a header file).
  * int: See "integer"
  * integer: TBD
  * libSDL: See "Simple DirectMedia Layer"
  * linear: TBD
  * macro: A C construct that looks similar to a C function, but is simply a #
    define that is expanded 'inline'. For example, if you declared the macro "#
    define ADD(A,B) ((A)+(B))", and then used it with "c = ADD(1,2);", that
    line of code would literally expand to "c = ((1) + (2));", or more simply,
    "c = 1 + 2;".
  * magic_api: A C structure that is passed along to a plugin's functions that
    exposes data and functions within the running copy of Tux Paint.
  * make: A utility that automatically determines which pieces of a larger
    program need to be recompiled, and issues the commands to recompile them.
    See also: "Makefile"
  * Makefile: A text file used by the "make" utility; it describes the
    relationships among files in your program, and the commands for updating
    each file. (For example, to compile a human-readable source-code file into
    a computer-readable executable program file.)
  * Magic tool: One of a number of effects or drawing tools in Tux Paint, made
    available via the "Magic" tool button.
  * Mix_Chunk *: (A pointer to) a C structure defined by SDL_mixer that
    contains a sound.
  * Mix_FreeChunk(): An SDL_mixer function that frees (deallocates) memory
    allocated for an SDL_mixer sound 'chunk' ("Mix_Chunk *").
  * Mix_LoadWAV(): An SDL_mixer function that loads a sound file (WAV, Ogg
    Vorbis, etc.) and returns it as a "Mix_Chunk *".
  * namespace: TBD
  * .ogg: See "Ogg Vorbis"
  * Ogg Vorbis: See also: "WAV"
  * Plugin: TBD
  * .png: Portable Network Graphics. An extensible file format for the
    lossless, portable, well-compressed storage of raster images. It's the file
    format Tux Paint uses to save images, and for its brushes and stamps. It's
    an easy way to store 32bpp RGBA images (24bpp true color with full 8bpp
    alpha transparency), excellent for use in graphics programs like Tux Paint.
    See also the "png(5)" man page)
  * pointer: See "C pointer"
  * prototype: See "C function prototype"
  * red: See "RGBA"
  * release: The action of releasing a button on a mouse.
  * RGBA: "Red, Green, Blue, Alpha." TBD
  * RGB: See "RGBA"
  * saturation: See "HSV"
  * SDL: See "Simple DirectMedia Layer"
  * SDL_FreeSurface(): An libSDL function that frees (deallocates) memory
    allocated for an SDL surface ("SDL_Surface *"). See also the
    "SDL_FreeSurface(3)" man page)
  * SDL_GetRGB(): A libSDL function that, given a Uint32 pixel value (e.g., one
    returned from the Tux Paint's Magic tool API helper function "getpixel()"),
    the format of the surface the pixel was taken from, and pointers to three
    Uint8 variables, will place the Red, Green and Blue (RGB) values of the
    pixel into the three Uint8 variables. (Example: "SDL_GetRGB(getpixel(surf,
    x, y), surf->format, &r, &g, &b);".) See also the "SDL_GetRGB(3)" man page)
  * SDL_MapRGB(): A libSDL function that, given the format of a surface and
    Uint8 values representing Red, Green and Blue values for a pixel, returns a
    Uint32 pixel value that can be placed in the surface (e.g., using Tux
    Paint's Magic tool API helper function "putpixel()"). (Example: "putpixel
    (surf, x, y, SDL_MapRGB(surf->format, r, g, b));".) See also the
    "SDL_MapRGB(3)" man page)
  * SDL_image: A library on top of libSDL that can load various kinds of image
    files (e.g., PNG) and return them as an "SDL_Surface *".
  * SDL_mixer: A library on top of libSDL that can load various kinds of sound
    files (WAV, Ogg Vorbis, etc.) and play back multiple sounds at once (mix
    them).
  * SDL_Rect: A C structure defined by libSDL that represents a rectangular
    area. It contains elements representing the coordinates of the top left
    corner of the rectange (x,y) and the dimensions of the rectangle (w,h). See
    also the "SDL_Rect(3)" man page)
  * SDL_Surface *: (A pointer to) a C structure defined by libSDL that contains
    a drawing surface. See also the "SDL_Surface(3)" man page)
  * Shared Object: A piece of code that's compiled separately from the main
    application, and loaded dynamically, at runtime.
  * Simple DirectMedia Layer: A programming library that allows programs
    portable low level access to a video framebuffer, audio output, mouse, and
    keyboard. (See also: http://www.libsdl.org/)
  * snprintf(): A C function, related to "printf()", which takes a 'format'
    string and one or more additional arguments, and puts them together.
    "snprintf()" takes the resulting output and stores it into a string, making
    sure not to go beyond the string's buffer size (which must also be
    supplied). For example, assume a string "char str[20];" has been declared;
    "snprintf(str, 20, "Name: %s, Age: %d", "Bill", "32");" will store "Name:
    Bill, Age: 32" into 'str'. See also the "snprintf(3)" man page)
  * .so: See "Shared Object"
  * sRBG: See "RGBA"
  * star: "*". A symbol in C that, when used in the declaration of variables
    (e.g., arguments to a function), denotes that the variable is a pointer.
    (For example, "int * p;" means that "p" is a pointer to an integer.) When
    used next to a pointer, it 'dereferences' the variable. (For example, later
    "*p = 50;" assigns the value of 50 to the memory that "p" points to; it
    does not change the value of "p", which is still a pointer to an integer.
    In essence, it changed the integer that's being pointed to.) See also:
    "ampersand"
  * strdup(): A C function that allocates enough memory to store a copy of a
    string, copies the string to it, and returns a "char *" pointer to the new
    copy. See also the "strdup(3)" man page)
  * struct: See "C structure"
  * tp_magic_api.h: A header file that defines Tux Paint's Magic tool API.
    Plugins must '#include' it.
  * tp-magic-config: A command-line program that provides information about the
    installed version of Tux Paint to plugin developers (such as what C
    compiler flags they should compile with, and where plugin shared objects
    and data files should be installed). See also the "tp-magic-config(3)" man
    page)
  * Uint32: A 32-bit, unsigned integer (defined by libSDL). In other words,
    four bytes that can represent 0 through 4294967295. (Typically used to hold
    enough information to store three or four bytes representing a pixel's
    color; i.e., RBGA value).
  * Uint8: An 8-bit, unsigned integer (defined by libSDL). In other words, a
    byte that can represent 0 through 255.
  * unsigned: In C, a variable that can store a numeric value can be declared
    as either "signed" (the default), or "unsigned". In the former case, one
    bit of the value is used to denote the sign of the value (either positive
    or negative). In the latter case, the value can only be positive, but
    benefits from one extra bit of storage for the number. A signed byte (8
    bits), for example, can represent any number between -128 and 127. An
    unsigned byte can go up to 255, but it cannot go below 0. For the purposes
    of graphics in SDL, unsigned values should be used for RGB values, since
    each channel (red, green and blue) may be between 0 (off) and 255
    (brightest).
  * value: See "HSV"
  * variable: A construct in computer programming that contains a value which
    can be referenced again later by referring to the variable's name, and
    typically changed later. For example, a variable to hold someone's age
    could be declared as an integer: "int a;". It can be examined later: "if (a
    >= 18) { /* they are an adult */ } else { /* they are not an adult */ }".
  * .wav: See also: "Ogg Vorbis"
  * (w,h): See "Dimensions"
  * (x,y): See "Coordinates"

