529 lines
20 KiB
HTML
529 lines
20 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html><head><title>Creating Tux Paint Magic Tool Plugins</title>
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<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
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</head>
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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#FF0000"
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alink="#FF00FF">
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<center>
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<h1>Creating Tux Paint Magic Tool Plugins</h1>
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<p>Copyright 2007-2007 by Bill Kendrick and others<br>
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New Breed Software</p>
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<p><a href="mailto:bill@newbreedsoftware.com">bill@newbreedsoftware.com</a><br>
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<a href="http://www.tuxpaint.org/">http://www.tuxpaint.org/</a></p>
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<p>July 5, 2007 - July 27, 2007</p>
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</center>
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<hr size=2 noshade>
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<h2>Overview</h2>
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<blockquote>
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<p>Beginning with version 0.9.18, Tux Paint's 'Magic' tools were converted
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from routines that lived within the application itself, to a set of 'plugins'
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that are loaded when Tux Paint starts up.</p>
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<p>This division allows more rapid development of 'Magic' tools, and allows
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programmers to create and test new tools without needing to integrate them
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within the main Tux Paint source code. (Users of more professional
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graphics tools, such as The GIMP, should be familiar with this plugin
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concept.)</p>
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</blockquote>
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<hr size=1 noshade>
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<h2>Prerequisites</h2>
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<blockquote>
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<p>Tux Paint is written in the C programming language, and uses the
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Simple DirectMedia Layer library ('libSDL', or simply 'SDL').
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Therefore, for the moment at least, one must understand the C language and
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how to compile C-based programs. Familiarity with the SDL API is highly
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recommended, but some basic SDL concepts will be covered in this document.</p>
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</blockquote>
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<hr size=1 noshade>
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<h2>Interfaces</h2>
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<blockquote>
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<p>Those who create 'Magic' tool plugins for Tux Paint must provide
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some interfaces (C functions) that Tux Paint may invoke.</p>
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<p>Tux Paint utilizes SDL's "SDL_LoadObject()" and "SDL_LoadFunction()"
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routines to load plugins (shared objects files; e.g., "<code>.so</code>"
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files on Linux or "<code>.dll</code>" files on Windows) and find the
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functions within.</p>
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<p>In turn, Tux Paint provides a number of helper functions that the
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plugin may (or sometimes is required to) use. This is exposed as a C
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structure (or "<code>struct</code>") which contains pointers to functions
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and other data inside Tux Paint. A pointer to this structure gets
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passed along to the plugin's functions as an argument when Tux Paint
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invokes them.</p>
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<p>Plugins should <code>#include</code> the C header file
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"<code>tp_magic_api.h</code>", which exposes the 'Magic' tool plugin API.
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Also, when you run the C compiler to build a plugin, you should use the
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command-line tool "<code>tp-magic-config</code>" to get the appropriate
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compiler flags (such as where the compiler can find the Tux Paint
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plugin header file, as well as SDL's header files) for building a plugin.</p>
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<p>The C header file and command-line tool mentioned above are included
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with Tux Paint — or in some cases, as part of a "Tux Paint
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'Magic' Tool Plugin Development package".</p>
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<h3>'Magic' tool plugin functions</h3>
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<blockquote>
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<p>'Magic' tool plugins <i>must</i> contain the functions listed below.
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<b>Note:</b> To avoid 'namespace' collisions, each function's name must
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start with the shared object's filename (e.g., "blur.so" or "blur.dll"
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would have functions whose names begin with "<code>blur_</code>"). <i>This
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includes private functions</i> (ones not used by Tux Paint directly),
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unless you declare those as '<code>static</code>'.</p>
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<h4>Common arguments to plugin functions:</h4>
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Here is a description of arguments that many of your plugin's functions
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will need to accept.
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<ul>
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<li><code><b>magic_api * api</b></code><br>
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Pointer to a C structure containing pointers to Tux Paint functions and
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other data that the plugin can (and sometimes should) use.
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The contents of this struct are <a href="#tpfuncs">described below</a>.<br>
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<br>
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Note: The <code>magic_api</code> struct is defined in the C header file
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"<code>tp_magic_api.h</code>", which you should include at the top of your
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plugin's C source file:
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<blockquote><code>
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#include "tp_magic_api.h"
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</code></blockquote>
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<li><code><b>int which</b></code><br>
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An index the plugin should use to differentiate different 'Magic' tools,
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if the plugin provides more than one. (If not, "which" will always be 0.)
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See <a href="#multiple">"Creating plugins with multiple effects"</a>,
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below.<br>
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<br>
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<li><code><b>SDL_Surface * snapshot</b></code><br>
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A snapshot of the previous Tux Paint canvas, taken when the the
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mouse was first clicked to activate the current magic tool. If you don't
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continuously affect the image during one hold of the mouse button,
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you should base your effects off the contents of this canvas.
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(That is, read from "<code>snapshot</code>" and write to
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"<code>canvas</code>", below.)<br>
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<br>
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<li><code><b>SDL_Surface * canvas</b></code><br>
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The current Tux Paint drawing canvas. Your magical effects should end
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up here!<br>
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<br>
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<li><code><b>SDL_Rect * update_rect</b></code><br>
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A pointer to an SDL 'rectangle' structure that you use to tell Tux Paint
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what part of the canvas has been updated. If your effect affects a
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32x32 area centered around the mouse pointer, you would fill the SDL_Rect
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as follows:
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<blockquote><code>
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update_rect->x = x - 16;<br>
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update_rect->y = y - 16;<br>
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update_rect->w = 32;<br>
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update_rect->h = 32;
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</code></blockquote>
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Or, if your effect changes the entire canvas (e.g., flips it upside-down),
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you'd fill it as follows:
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<blockquote><code>
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update_rect->x = 0;<br>
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update_rect->y = 0;<br>
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update_rect->w = canvas->w;<br>
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update_rect->h = canvas->h;
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</code></blockquote>
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Note: "<code>update_rect</code>" is a C pointer
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(an "<code>SDL_Rect *</code>" rather than just an
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"<code>SDL_Rect</code>") because you need to fill in its contents.
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Because it is a pointer, you access its elements via
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"<code>-></code>" (arrow) rather than "<code>.</code>" (dot).
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</ul>
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<h4>Required plugin functions:</h4>
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<blockquote>
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<p>Your plugin is required to contain, at the least, all of the
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following functions.</p>
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<p><b>Note:</b> Remember, your plugin's function names must be
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preceded by your plugin's filename. That is, if your plugin is called
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"<code>zoom.so</code>" (on Linux) or "<code>zoom.dll</code>" (on Windows),
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then the names of your functions must begin with "<code><b>zoom_</b></code>"
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(e.g., "<code>zoom_get_name(...)</code>").</p>
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<h5>Plugin "housekeeping" functions:</h5>
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<ul>
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<li><code><b>Uint32 api_version(void)</b></code><br>
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The plugin should return an integer value representing the version of
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the Tux Paint 'Magic' tool plugin API the plugin was built against.
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The safest thing to do is return the value of
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<code>TP_MAGIC_API_VERSION</code>, which is defined in
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"<code>tp_magic_api.h</code>". If Tux Paint deems your plugin to
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be compatible, it will go ahead and use it.<br>
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<br>
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<b>Note:</b> Called once by Tux Paint, at startup. It is called
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first.<br>
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<li><code><b>int init(magic_api * api)</b></code><br>
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The plugin should do any initialization here.
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Return '1' if initialization was successful,
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or '0' if not (and Tux Paint will not present any 'Magic' tools
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from the plugin).<br>
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<br>
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<b>Note:</b> Called once by Tux Paint, at startup. It is called
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first. It is called after "<code>api_version()</code>", if
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Tux Paint believes your plugin to be compatible.<br>
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<li><code><b>int get_tool_count(magic_api * api)</b></code><br>
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This should return the number of Magic tools this plugin provides to
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Tux Paint.<br>
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<br>
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<b>Note:</b> Called once by Tux Paint, at startup. It is called
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after your "<code>init()</code>", if it succeeded.<br>
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<br>
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<li><code><b>char * get_name(magic_api * api, int which)</b></code><br>
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This should return a string containing the name of a magic tool.
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This will appear on the button in the 'Magic' selector within
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Tux Paint.<br>
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<br>
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Tux Paint will <code>free()</code> the string upon exit, so you should
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wrap it in a C <code>strdup()</code> call.<br>
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<br>
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<b>Note:</b> Called once for each Magic tool your plugin claims to
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contain (by your "<code>get_tool_count()</code>").<br>
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<br>
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<li><code><b>SDL_Surface * get_icon(magic_api * api, int which)</b></code><br>
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This should return an SDL_Surface containing the icon representing
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the tool. (A greyscale image with alpha, no larger than 40x40.)
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This will appear on the button in the 'Magic' selector within
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Tux Paint.<br>
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<br>
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Tux Paint will free ("<code>SDL_FreeSurface()</code>") the surface upon
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exit.<br>
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<br>
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<b>Note:</b> Called once for each Magic tool your plugin claims to
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contain (by your "<code>get_tool_count()</code>").<br>
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<br>
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<li><code><b>char * get_description(magic_api * api, int which)</b></code><br>
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This should return a string containing the description of a magic tool.
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This will appear as a help tip, explained by Tux the Penguin, within
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Tux Paint.<br>
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<br>
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Tux Paint will <code>free()</code> the string upon exit, so you should
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wrap it in a C <code>strdup()</code> call.<br>
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<br>
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<b>Note:</b> Called once for each Magic tool your plugin claims to
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contain (by your "<code>get_tool_count()</code>").<br>
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<br>
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<li><code><b>int requires_colors(magic_api * api, int which)</b></code><br>
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Return a '1' if the 'Magic' tool accepts colors (the 'Colors' palette in
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Tux Paint will be available), or '0' if not.<br>
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<br>
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<b>Note:</b> Called once for each Magic tool your plugin claims to
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contain (by your "<code>get_tool_count()</code>").<br>
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<br>
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<li><code><b>void shutdown(magic_api * api)</b></code><br>
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The plugin should do any cleanup here. If you allocated any memory
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or used SDL_Mixer to load any sounds during <code>init()</code>,
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for example, you should <code>free()</code> the allocated memory
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and <code>Mix_FreeChunk()</code> the sounds here.<br>
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<br>
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<b>Note:</b> This function is called once, when Tux Paint exits.<br>
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<br>
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</ul>
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<h5>Plugin event functions:</h5>
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<ul>
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<li><code><b>void set_color(magic_api * api, Uint8 r, Uint8 g, Uint8 g)
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</b></code><br>
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Tux Paint will call this function to inform the plugin of the
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RGB values of the currently-selected color in Tux Paint's
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'Colors' palette. (It will be called whenever one of the plguin's
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Magic tools that accept colors becomes active, or the user picks a new
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color while such a tool is currently active.)<br>
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<br>
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<li><code><b>void click(magic_api * api, int which, SDL_Surface * snapshot,
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SDL_Surface * canvas, int x, int y, SDL_Rect * update_rect)
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</b></code><br>
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The plugin should apply the appropriate 'Magic' tool on the 'canvas'
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surface. The (x,y) coordinates are where the mouse was (within the canvas)
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when the mouse button was clicked.<br>
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<br>
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The plugin should report back what part of the canvas was affected, by
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filling in the (x,y) and (w,h) values in 'update_rect'.<br>
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<br>
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The contents of the drawing canvas immediately prior to the mouse button
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click is stored within the 'snapshot' canvas.<br>
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<br>
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<li><code><b>void drag(magic_api * api, int which, SDL_Surface * snapshot,
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SDL_Surface * canvas, int ox, int oy, int x, int y,
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SDL_Rect * update_rect)</b></code><br>
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The plugin should apply the appropriate 'Magic' tool on the 'canvas'
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surface. The (ox,oy) and (x,y) coordinates are the location of the mouse
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at the beginning and end of the stroke. Typically, plugins that let the
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user "draw" effects onto the canvas call the Tux Paint 'Magic' tool
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plugin "line()" helper function. (See below).<br>
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<br>
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The plugin should report back what part of the canvas was affected, by
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filling in the (x,y) and (w,h) values in 'update_rect'.<br>
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<br>
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Note: The contents of the drawing canvas immediately prior to the mouse
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button click remains as it was (when the plugin's "click()" function was
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called), and is still available in the 'snapshot' canvas.<br>
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<br>
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<li><code><b>void release(magic_api * api, int which, SDL_Surface * snapshot,
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SDL_Surface * canvas, int x, int y,
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SDL_Rect * update_rect)</b></code><br>
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The plugin should apply the appropriate 'Magic' tool on the 'canvas'
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surface. The (x,y) coordinates are where the mouse was (within the canvas)
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when the mouse button was released.<br>
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<br>
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The plugin should report back what part of the canvas was affected, by
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filling in the (x,y) and (w,h) values in 'update_rect'.<br>
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<br>
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<b>Note:</b> The contents of the drawing canvas immediately prior to the mouse
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button click remains as it was (when the plugin's "click()" function was
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called), and is still available in the 'snapshot' canvas.<br>
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<br>
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</ul>
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</blockquote>
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</blockquote>
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<h3><a name="tpfuncs">Tux Paint Functions</a></h3>
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<blockquote>
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<p>Tux Paint provides a number of helper functions that plugins may
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access via the "magic_api" structure, sent to all of the plugin's functions
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(see above).</p>
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<ul>
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<li><code><b>Uint32 getpixel(SDL_Surface * surf, int x, int y)</b></code>
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Retreives the pixel value from the (x,y) coordinates of an SDL_Surface.
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(You can use SDL's "SDL_GetRGB()" function to convert the Uint32 'pixel'
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to a set of Uint8 RGB values.)<br>
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<br>
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<li><code><b>void putpixel(SDL_Surface * surf, int x, int y, Uint32 pixel)
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</b></code><br>
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Sets the pixel value at position (x,y) of an SDL_Surface.
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(You can use SDL's "SDL_MapRGB()" function to convert a set of Uint8
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RGB values to a Uint32 'pixel' value appropriate to the destination
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surface.)<br>
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<br>
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<li><code><b>int in_circle(int x, int y, int radius)</b></code><br>
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Returns '1' if the (x,y) location is within a circle of a particular
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radius (centered around the origin: (0,0)). Returns '0' otherwise.
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Useful to create 'Magic' tools that affect the canvas with a circular
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brush shape.<br>
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<br>
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<li><code><b>void show_progress_bar(void)</b></code><br>
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Asks Tux Paint to animate and draw one frame of its progress bar
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(at the bottom of the screen). Useful for routines that may take a
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long time, to provide feedback to the user that Tux Paint has not
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crashed or frozen.<br>
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<br>
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<li><code><b>void tuxpaint_version(int * major, int * minor, int * revision)
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</b></code><br>
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Returns the version of Tux Paint being used (e.g., "0.9.18"),
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separated into three integers.<br>
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<br>
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<li><code><b>void line(int which, SDL_Surface * canvas, SDL_Surface * snapshot,
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int x1, int y1, int x2, int y2, int step, FUNC callback)</b></code><br>
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This function calculates all points on a line between the coordinates
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(x1,y1) and (x2,y2). Every 'step' iterations, it calls the 'callback'
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function.<br>
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<br>
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It sends the 'callback' function the (x,y) coordinates on the line,
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Tux Paint's "magic_api" struct (as a "void *" pointer),
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a 'which' value, represening which of the plugin's 'Magic' tool is
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being used, and the current and snapshot canvases.<br>
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<br>
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Example prototype of a callback function that may be sent to
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Tux Paint's "line()" 'Magic' tool plugin helper function:
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<blockquote><code>
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void exampleCallBack(void * ptr_to_api, int which_tool,
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SDL_Surface * canvas, SDL_Surface * snapshot, int x, int y);
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</code></blockquote>
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<li><code><b>void playsound(Mix_Chunk * snd, int pan, int dist)</b></code><br>
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This function plays a sound (one loaded by the SDL helper library
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"SDL_mixer"). It uses SDL_mixer's "Mix_SetPanning()" to set the volume
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of the sound on the left and right speakers, based on the 'pan' and 'dist'
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values sent to it.<br>
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<br>
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A 'pan' of 128 causes the sound to be played at equal volume on the left
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and right speakers. A 'pan' of 0 causes it to be played completely on the
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left, and 255 completely on the right.<br>
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<br>
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The 'dist' value affects overall volume. 255 is loudest, and 0 is silent.<br>
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The 'pan' and 'dist' values can be used to simulate location and distance of
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the 'Magic' tool effect.<br>
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<br>
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<li><code><b>void special_notify(int flag)</b></code><br>
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This function notifies Tux Paint of special events. Various values
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defined in "tp_magic_api.h" can be logically 'or'ed together and sent to
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this function.
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<ul>
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<li>SPECIAL_FLIP — The contents of the canvas has been flipped.
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If a 'Starter' image was used as the basis of this image, it should be
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flipped too, and a record of the flip should be stored as part of
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Tux Paint's undo buffer stack. Additionally, the fact that the
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starter has been flipped (or unflipped) should be recorded on disk
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when the current drawing is saved.
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<li>SPECIAL_MIRROR — Similar to SPECIAL_FLIP, but for magic tools
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that mirror the contents of the canvas.
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</ul>
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<br>
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<li><code><b>int button_down(void)</b></code><br>
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A '1' is returned if the mouse button is down; '0' otherwise.<br>
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<br>
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<li><code><b>float sRGB_to_linear(Uint8 srbg)</b></code><br>
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Converts an 8-bit sRGB value (one between 0 and 255) to a linear
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floating point value (between 0.0 and 1.0).<br>
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<br>
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<li><code><b>uint8 linear_to_sRGB(float linear)</b></code><br>
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Converts a linear floating point value (one between 0.0 and 1.0) to
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an 8-bit sRGB value (between 0 and 255).<br>
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<br>
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</ul>
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</blockquote>
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</blockquote>
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<hr size=1 noshade>
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<h2>Compiling</h2>
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<blockquote>
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<h3>Linux and other Unix-like Platforms</h3>
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<blockquote>
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<p>Use the C compiler's "<code>-shared</code>" command-line option to generate
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a shared object file ("<code>.so</code>") based on your 'Magic' tool
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plugin's C source code.</p>
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<p>Additionally, use the "<code>tp-magic-config --cflags</code>" command,
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supplied as part of Tux Paint, to provide additional command-line
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flags to your C compiler that will help it build your plugin.</p>
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<p>As a stand-alone command, using the GNU C Compiler and BASH shell,
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for example:</p>
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<blockquote>
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<p><code>
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gcc -shared `tp-magic-config --cflags` my_plugin.c -o my_plugin.so
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</code></p>
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</blockquote>
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<p><b>Note:</b> The characters around the "<code>tp-magic-config</code>"
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command are a grave/backtick/backquote
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("<code><b><font size=+1>`</font></b></code>"), and
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not an apostrophe/single-quote ("<code><b><font size=+1>'</font></b></code>").
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They tell the shell to execute the command within (in this case,
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"<code>tp-magic-config ...</code>"), and use its output
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as an argument to the command being executed (in this case,
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"<code>gcc ...</code>").</p>
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<p>A snippet from a more generalized Makefile might look like this:</p>
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<blockquote>
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<p><code>
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CFLAGS=-Wall -O2 $(shell tp-magic-config --cflags)<br>
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<br>
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my_plugin.so: my_plugin.c
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$(CC) -shared $(CFLAGS) -o $@ $<
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</code></p>
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</blockquote>
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<p>You may then install it globally into:
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<code>/usr/lib/tuxpaint/plugins/</code> or
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<code>/usr/local/lib/tuxpaint/plugins/</code> (depending on how
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Tux Paint was installed).</p>
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<p>Or install it locally (for the current user only) into:
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<code>~/.tuxpaint/magic/</code><br>
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(<b>FIXME:</b> As of 2007-07-27, Tux Paint does not look here yet!)</p>
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</blockquote>
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<h3>Windows</h3>
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<blockquote>
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<p>TBD</p>
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</blockquote>
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<h3>Mac OS X</h3>
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<blockquote>
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<p>TBD</p>
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</blockquote>
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</blockquote>
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<hr size=1 noshade>
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<h2><a name="multiple">Creating plugins with multiple effects</a></h2>
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<blockquote>
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TBD
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</blockquote>
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<hr size=1 noshade>
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<h2>Example Code</h2>
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<blockquote>
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TBD
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</blockquote>
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<hr size=1 noshade>
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<p>Summary and contact info TBD.</p>
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</body></html>
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