349 lines
13 KiB
HTML
349 lines
13 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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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#FF0000"
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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 6, 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,
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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 should) use. This is exposed as a C structure
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(containing pointers to functions inside Tux Paint and other data)
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that gets passed along to the plugin's functions as an argument.</p>
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<p>Plugins should <code>#include</code> the file "<code>tp_magic_api.h</code>",
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and compiler flags which should be used when building plugins (to find the
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aforementioned header file, as well as SDL's header files) can be acquired
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by invoking the tool "<code>tp-magic-config</code>".</p>
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<p>(These are included with Tux Paint — or in some cases, as part
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of a "Tux Paint '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 must provide 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 "blur_").</p>
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<h4>Common arguments to plugin functions:</h4>
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<ul>
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<li>magic_api * api<br>
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Pointer to the struct containing pointers to Tux Paint functions and
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other data (see below)
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<li>int which<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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<li>SDL_Surface * canvas<br>
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The active Tux Paint drawing canvas. Your magical effects should end
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up here!
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<li>SDL_Surface * last<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 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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</ul>
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<h4>Required plugin functions:</h4>
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<ul>
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<li>int get_tool_count(magic_api * api)<br>
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This should return the number of Magic tools this plugin provides to
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Tux Paint.
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<li>char * get_name(magic_api * api, int which)<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 Tux Paint.
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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.
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<li>SDL_Surface * get_icon(magic_api * api, int which)<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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Tux Paint will SDL_FreeSurface() the surface upon exit.
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<li>char * get_description(magic_api * api, int which)<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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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.
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<li>int requires_colors(magic_api * api, int which)<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.
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<li>void set_color(magic_api * api, Uint8 r, Uint8 g, Uint8 g)<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.)
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<li>Uint32 api_version(void)<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 it was built against.
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Simply return TP_MAGIC_API_VERSION, which is defined in
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"tp_magic_api.h", to satisfy this requirement.
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<li>int init(magic_api * api)<br>
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The plugin should do any initialization here. This function is called once,
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at Tux Paint startup. 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).
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<li>void shutdown(magic_api * api)<br>
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The plugin should do any cleanup here. This function is called once,
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at Tux Paint exit.
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<li>void click(magic_api * api, int which, SDL_Surface * snapshot,
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SDL_Surface * canvas, int x, int y)<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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The contents of the drawing canvas immediately prior to the mouse button
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click is stored within the 'snapshot' canvas.
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<li>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)<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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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.
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</blockquote>
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<h3>Tux Paint Functions</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>Uint32 getpixel(SDL_Surface * surf, int x, int y)
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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.)
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<li>void putpixel(SDL_Surface * surf, int x, int y, Uint32 pixel)<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.)
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<li>int in_circle(int x, int y, int radius)<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.
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<li>void show_progress_bar(void)<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.
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<li>void tuxpaint_version(int * major, int * minor, int * revision)<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.
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<li>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)<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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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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<p>Example prototype of a callback function that may be sent to
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Tux Paint's "line()" 'Magic' tool plugin helper function:</p>
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<blockquote>
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<p><code>void exampleCallBack(void * ptr_to_api, int which_tool,
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SDL_Surface * canvas, SDL_Surface * snapshot, int x, int y);</code></p>
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</blockquote>
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<li>void playsound(Mix_Chunk * snd, int pan, int dist)<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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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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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.
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<li>void special_notify(int flag)<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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<li>int button_down(void)<br>
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A '1' is returned if the mouse button is down; '0' otherwise.
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<li>float sRGB_to_linear(Uint8 srbg)<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).
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<li>uint8 linear_to_sRGB(float linear)<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).
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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 "-shared" 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 "tp-magic-config --cflags" 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>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>Then install globally into: /usr/[local/]lib/tuxpaint/.
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Or locally into: ~/.tuxpaint/magic/</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>Example Code</h2>
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<blockquote>
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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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