Note: This document is short and highly incomplete. If you want to write a new,
decent one, it will be more than welcome!



Basic principles
================

A skin (or theme, the two words have almost the same meaning) for VLC is made
of many BMP files (Windows Bitmap format) containing all the images needed, and
of an XML file describing how these images should be displayed, what happens
when the user clicks on a button, etc.

Those of you who have already done skins for other softwares shouldn't have too
many difficulties to understand how all this works.



Bezier curves
=============

One cool thing with VLC sliders is that they are not necessarily rectilinear,
but they can follow any Bezier curve. So if you want to have a slider moving
on a half-circle, or even doing a loop, you can !

This is not the place to explain how these curves work, the only thing to know
is that a Bezier curve can be caracterised by a set of points. Once you have
them (thanks to the graphical utility presented at the end of this file, for
example), you just need to enter the list of abscissas in the 'abs' attribute
and the list of ordinates (in the same order...) in the 'ord' attribute. The
separator is the coma. Example: abs="2,45,88" ord="50,120,50"

Bezier curves are used for the SliderControl and the PlaylistControl tags.



The bitmaps
===========

Basically, you need one bitmap file by state of control. For example, with a
image control you'll need 1 image, with a button 2 images (or 3 if you provide
the disabled state). A slider will also need 2, one for the static part and
another for the mobile part. Of course, the same bitmap file can be used for
many controls, provided you want to display the same image!

The bitmap format doesn't allow a transparent color, but in the XML file you
can specify a color that will be considered as transparent wherever it appears
in the bitmap file.



The XML file
============

XML is a markup language, like HTML. It won't be explained here any further,
please use Google if you don't know what is XML. You'll see, it's rather easy
to understand.

The XML file used for the VLC skins follows a predefined DTD. You can find this
DTD in VLC CVS, and its reading is strongly advised, since it contains most of
the default values used for the parameters. A skin that doesn't follow the DTD
with which VLC was compiled won't be loaded by VLC (and it might even crash
it...).

For a better comprehension of what follows, you should have a look at the DTD
(in modules/gui/skin/parser/dkin.dtd) and/or at an example of valid xml skin
(such as modules/gui/skin/skins/default/theme.xml).

OK, let's go for an enumeration of the different tags and theor attributes :

 - Theme: The main tag.
   Attributes:
     - magnet: allows to select the range of action (in pixels) of magnetism
       with border of screen : that is to say when the distance between the
       border of the screen and a window is less than this value, the window
       will stick to the border. 0 means no magnetism.
       Default is "9".

 - ThemeInfo: You can enter here some information about you (but this
   information is currently unused by VLC...)
   Attributes :
     - name: not yet supported.
     - author: not yet supported.
     - email: not yet supported.
     - webpage: not yet supported.

 - Bitmap: Associates a bitmap file with a name (=identifiant) that will be
   used by the various controls. Obviously, you need one Bitmap tag for each
   bitmap file you have.
   Attributes:
     - id: this is the name of the bitmap that will be used with controls
       (2 bitmaps shouldn't have the same name).
     - alphacolor: this is the transparency color of the bitmap. It must be
       indicated with the following format: "#RRGGBB" (where RR stands for the
       hexadecimal value of the red component, GG for the green one, and BB for
       the blue one).
     - file: this attribute is used to indicate the path and name of the bitmap
       file used. This path can be absolute (but you should avoid it as often as
       possible), or relative to the path of the xml file.

 - Event: An action that will be associated to a control later.
   Attributes :
     - id: this is the name of the event that will be used with controls.
       (2 events shouldn't have the same name).
     - event: see events-howto.txt
     - key: this is the shortcut key associated with the event. This means that
       the event will be executed when hitting the correspounding key. It must
       be indicated with the following format : "MOD+L" where "MOD" is the
       modifier key ("CTRL" or "ALT") and "L" is the letter in uppercase
       ("MOD+" is optionnal).
       Default is "none".

 - Font: Declares a font to be used in a TextControl or PlaylistControl.
   Attributes :
      - id: this is the name of the font that will be used with controls.
        Default is "default". (2 fonts shouldn't have the same name).
      - font: this is the name of the font
        Default is "arial".
      - size: this is the size of the font in points (pt).
        Default is "12".
      - color: this is the color of the font with the following format,
        "#RRGGBB" (see Bitmap).
        Default is "#000000" (black).
      - weight: this is the weight of the font. It must be between 0 and 1000
        Default is "400" (normal weight). Fewer is thinner...
      - italic: sets if the font must be in italic format.
        Default is "false".
      - underline: sets if the font must be underlined.
        Default is "false".

 - Window: A window that will appear on screen.
      - id: this is the name of the window (it will be only used for events
        but it is important: 2 windows shouldn't have the same name).
      - visible: sets if the window should appear or not at the launch of VLC.
        Default is "true".
      - x: sets the left position of the window.
        Default is "0".
      - y: sets the top position of the window.
        Default is "0".
      - fadetime: sets the time in milliseconds of the hide/show fading
        transition.
        Default is "500".
      - alpha: sets the transparency of the window. It must be between 1 and
        255. 1 is nearly total transaprency and should be avoided. 255 is total
        opacity.
        Default is "255". You should use high values.
      - movealpha: sets the transparency of the window when the window is
        moving. Same range as alpha.
        Default is "255".
      - dragdrop: sets if drag and drop of media files is allowed in this
        window.
        Default is "true".
      - playondrop: sets if a drop file is played directly (true) or only
        enqueud (false). This has no effect if dragdrop is set to "false".
        Default is "true".

 - ControlGroup: Adds an offset to the elements it contains. A ControlGroup is
   only supposed to ease the job of the skin designer, who can adjust the
   position of a group of controls without modifying all the coordinates, but
   you can ignore it if you want (only one ControlGroup is necessary, just
   inside Window). ControlGroup tags can be nested.
   Attributes :
     - x: try and guess.
       Default is "0".
     - y: what do you think ?
       Default is "0".

 - Anchor: Creates a "magnetic point" in the current Window. If an anchor of
   another Window enters in the range of action of this anchor, the 2 anchors
   will automatically be on the same place, and the windows are "sticked". Each
   anchor has a priority ('priority' attribute), and the anchor with the
   highest priority is the winner, which means that when moving its Window all
   the other anchored Windows will move too. To break the effect of 2 linked
   anchors, you need to move the Window whose anchor has the lower priority.
   Attributes :
     - x: is it really necessary to explain ?
       Default is "0".
     - y: ...
       Default is "0".
     - priority: priority of anchor (see the previous description).
       No default, must de defined!
     - range: Range of action of the anchor in pixels.
       Default is "10".

 - ImageControl, ButtonControl, CheckBoxControl, TextControl, SliderControl,
   PlaylistControl: The various visual controls that constitute a Window. They
   share some properties: 'x' and 'y' for the position, 'visible' for the
   initial state, 'id' for identifying them (only needed if you want to create
   an event acting on this particular control) and 'help' for a short
   description of the control that could be displayed in a special TextControl
   (see below). All the controls can also accept events, and you have the
   possibility to associate many events to a control at once, separing them
   with semicolons.

 - ImageControl: Creates a simple image. Useful for backgrounds.
     - image: this attribute must be set to an identifiant of a Bitmap tag.
     - onclick: the 'event' attribute can be used to associate an event to the
       image (the event is triggered by a click on the image).
       Typical use: an Event made with 'WINDOW_MOVE(window)' (where 'window' is
       the id of a Window) can be associated to an ImageControl of this
       Window. Hence the Window can be moved via the image...

 - ButtonControl: Creates a button.
     - up: identifiant of a Bitmap. Used for drawing the up state of the
       button.
     - down: identifiant of a Bitmap. Used for drawing the down state of the
       button.
     - disabled : identifiant of a Bitmap. Used for drawing the disabled state
       of the button.
     - onclick: event executed when clicking on the button.
       Default is "none".
     - onmouseover: event executed when the mouse cursor enters the button.
       Default is "none".
     - onmouseout: event executed when the mouse cursor leaves the button.
       Default is "none".
     - tooltiptext : used to display a tooltip.
       Default is "none" (no tooltip).

 - CheckBoxControl: Creates a checkbox, i.e. a button with 2 states
   (checked/unchecked). So you need 6 images for a full-featured checkbox: each
   state has a basic image, an image corresponding to a click not yet released,
   and an image for the disabled control. If you supply only the basic images,
   the other ones will be identical.
   Attributes:
     - img1: identifiant of a Bitmap. Used for drawing control in state 1.
     - clickimg1: identifiants of a bitmap. Used for drawing control when
       clicking on it in state 1.
       Default is the value of 'img1' attribute.
     - img2: identifiant of a Bitmap. Used for drawing control in state 2.
     - clickimg2: identifiant of a Bitmap. Used for drawing control when
       clicking on it in state 2.
       Default is the value of 'img2' attribute.
     - disabled1: identifiant of a Bitmap. Used for drawing control in state 1
       when disabling.
       Default is the value of 'img1' attribute.
     - disabled2: identifiant of a Bitmap. Used for drawing control in state 1
       when disabling.
       Default is the value of 'img2' attribute.
     - onclick1: event executed when clicking on the control in state 1.
       Default is "none".
     - onclick2: event executed when clicking on the control in state 2.
       Default is "none".
     - onmouseover1: event executed when the mouse cursor enters the button in
       state 1.
       Default is "none".
     - onmouseout1: event executed when the mouse cursor leaves the button in
       state 1.
       Default is "none".
     - onmouseover2: event executed when the mouse cursor enters the button in
       state 2.
       Default is "none".
     - onmouseout2: event executed when the mouse cursor leaves the button in
       state 2.
       Default is "none".

 - TextControl: Creates a text.
   Attributes:
     - font: the font to use, which must be one of the Font identifiants.
     - text: the text to display.
     - align: either 'left' or 'center' or 'right'.
       Default is "left".
     - scroll: if set to 'true', the text will scroll if it does not fit into
       the 'scrollspace'.
       Default is "true".
     - scrollspace: size in pixel between two occurrences of the text when
       scrolling.
       Default is "20".
     - display: this value is a bit special, it allows to have a text
       auto-updated by VLC. Possible values are 'time', 'left_time',
       'total_time', 'file_name' (for the current file name with its path),
       'title' (for the file name without the path) and 'help' (for a help
       about the controls that defined their 'help' attribute).
       You can specify several types by separating them with semicolons. To
       switch between then, just double click on the text.
       Useful to switch between 'time' and 'left_time'.
     - width: Width of the text in pixels. If set to "0", the width is
       automatically calculated to fit with the current text.
       Default is "0".

 - SliderControl: Creates a slider. The 'abs' and 'ord' attributes are needed
   for the Bezier curve that the slider will follow. 'up' and 'down' are the
   images of the slider. The 'tooltiptext' attribute works, and the slider will
   automatically append the percentage of the position.
   Attributes:
     - type: two 'types' of sliders are predefined: 'time' for a slider
       allowing to seek in the stream, and 'volume' for a volume slider.
       Default is "time".
     - up: identifiant of a Bitmap.
     - down: identifiant of a Bitmap.
     - abs: see SliderControl description and bezier curve description.
     - ord: see SliderControl description and bezier curve description.
     - tooltiptext: used to display a tooltip.
       Default is "none" (no tooltip).

 - PlaylistControl: Creates a playlist. This tag must contain a SliderControl
   tag (to allow scrolling in the playlist). If the playlist contains entries
   wider than the list width, an automatic tooltip will appear with
   the full name of the entry. The other attributes are rather easy to
   understand...
   Attributes:
     - width: width of the list in pixels. This is the whole width for file
       name, number of files in the playlist and info text.
       Default is "200".
     - infowidth: width of the info text in pixels.
       Default is "50".
     - font: the font to use, which must be one of the Font identifiants.
     - playfont: the font to use for current playing file, which must be one of
       the Font identifiants.
       Default is "none".
     - selcolor: color in "#RRGGBB" format of the selected files.
       Default is "#0000FF" (blue).
     - abs: see PlaylistControl description and bezier curve description.
     - ord: see PlaylistControl description and bezier curve description.



Compression
===========

Once your skin is finished, instead of keeping many bitmap files and the XML
file, you can compress them in a .tar.gz archive (Winzip and UmtimateZip can do
it perfectly, for example). Before doing so, don't forget to rename your XML
file into "theme.xml", or VLC won't be able to read it... Then rename your
compressed file with the .vlt extension and... that's all! VLC can load
directly skins with the .vlt extension.



Tools and advice
================

 - To generate easily Bezier curves, you can use the curve-maker. Basically,
   you add and remove points at will, and you can move them to see how the
   curve evolves. When you have reached the perfect curve, you just have to
   copy-paste the list of abscissas and ordinates into the 'abs' and 'ord'
   attributes of your SliderControl or PlaylistControl. The curve-maker also
   allows to load a bitmap, this could be useful if you want to follow a
   specific pattern of a slider, for example.

 - When you are creating your skin, you may want to see the VLC messages where
   some errors are logged. For this, open a dos window, go to the directory
   where VLC is installed, and type "vlc -I skin -v --extraintf logger". This
   should open VLC and a log window (what's more, the logs should be saved in a
   file called vlc-log.txt). The interesting lines are those with "skin
   interface"...

 - For the Bitmap tags, don't use absolute paths but relative paths (they are
   relative to the XML file directory), so that your skin can be reused by
   anybody without a particular file structure.

 - To fully use the possibilities given, you should look at how other skins are
   made, it's often very useful.


Good luck!