path: root/specs/ch11.xml

<chapter id='keyboard_geometry'>
<title>Keyboard Geometry</title>

<para>
The XKB description of a keyboard includes an optional keyboard geometry which
describes the physical appearance of the keyboard. Keyboard geometry describes
the shape, location and color of all keyboard keys or other visible keyboard
components such as indicators. The information contained in a keyboard geometry
is sufficient to allow a client program to draw an accurate two-dimensional
image of the keyboard.
</para>


<para>
The components of the keyboard geometry include the following:
</para>

<itemizedlist>
<listitem>
  <para>A <emphasis>
symbolic name</emphasis>
 to help users identify the keyboard.
  </para>
</listitem>
<listitem>
  <para>The <emphasis>
width</emphasis>
 and <emphasis>
height</emphasis>
 of the keyboard, in <mediaobject>
 <imageobject> <imagedata format="SVG" fileref="XKBproto-8.svg"/>
 </imageobject>
 </mediaobject>
. For non-rectangular keyboards, the width and height describe the smallest
bounding-box that encloses the outline of the keyboard.
  </para>
</listitem>
<listitem>
  <para>A list of up to <emphasis>
MaxColors</emphasis>
 (<emphasis>
32</emphasis>
) <emphasis>
color names</emphasis>
. A color name is a string whose interpretation is not specified by XKB. Other
geometry components refer to colors using their indices in this list.
  </para>
</listitem>
<listitem>
  <para>The<emphasis>
 base color</emphasis>
 of the keyboard is the predominant color on the keyboard and is used as the
default color for any components whose color is not explicitly specified.
  </para>
</listitem>
<listitem>
  <para>The <emphasis>
label color</emphasis>
 is the color used to draw the labels on most of the keyboard keys.
  </para>
</listitem>
<listitem>
  <para>The <emphasis>
label font</emphasis>
 is a string which describes the font used to draw labels on most keys; XKB
does not specify a format or name space for font names.
  </para>
</listitem>
<listitem>
  <para>A list of <emphasis>
geometry properties</emphasis>
. A geometry property associates an arbitrary string with an equally arbitrary
name. Geometry properties can be used to provide hints to programs that display
images of keyboards, but they are not interpreted by XKB. No other geometry
structures refer to geometry properties.
  </para>
</listitem>
<listitem>
  <para>A list of <emphasis>
key aliases</emphasis>
, as described in <link linkend='symbolic_names'>Symbolic
Names</link>.
  </para>
</listitem>
<listitem>
  <para>A list of <emphasis>
shapes</emphasis>
; other keyboard components refer to shapes by their index in this list. A
shape consists of a name and one or more closed-polygons called <emphasis>
outlines</emphasis>
. Shapes and outlines are described in detail in <link linkend='shapes_and_outlines'>Shapes and Outlines</link>.
  </para>
</listitem>
</itemizedlist>

<para>
Unless otherwise specified, geometry measurements are in <mediaobject>
 <imageobject> <imagedata format="SVG" fileref="XKBproto-9.svg"/>
 </imageobject>
 </mediaobject>

 units. The origin (0,0) is in the top left corner of the keyboard image. Some
geometry components can be drawn rotated; all such objects rotate about their
origin in <mediaobject>
 <imageobject> <imagedata format="SVG" fileref="XKBproto-10.svg"/>
 </imageobject>
 </mediaobject>

 increments.
</para>


<para>
All geometry components include a <emphasis>
priority</emphasis>
, which indicates the order in which overlapping objects should be drawn.
Objects are drawn in order from highest priority (<emphasis>
0</emphasis>
) to lowest (<emphasis>
255</emphasis>
).
</para>


<para>
The description of the actual appearance of the keyboard is subdivided into
named <emphasis>
sections</emphasis>
 of related keys and <emphasis>
doodads</emphasis>
. A a <emphasis>
doodad</emphasis>
 describes some visible aspect of the keyboard that is not a key. A section is
a collection of keys and doodads that are physically close together and
logically related.
</para>

<sect1 id='shapes_and_outlines'>
<title>Shapes and Outlines</title>

<para>
An outline is a list of one or more points which describes a single
closed-polygon, as follows:
</para>

<itemizedlist>
<listitem>
  <para>A list with a single point describes a rectangle with one corner at the
origin of the shape (<emphasis>
0</emphasis>
,<emphasis>
0</emphasis>
) and the opposite corner at the specified point.
  </para>
</listitem>
<listitem>
  <para>A list of two points describes a rectangle with one corner at the
position specified by the first point and the opposite corner at the position
specified by the second point.
  </para>
</listitem>
<listitem>
  <para>A list of three or more points describes an arbitrary polygon. If
necessary, the polygon is automatically closed by connecting the last point in
the list with the first.
  </para>
</listitem>
<listitem>
  <para>A non-zero value for the <emphasis>
cornerRadius</emphasis>
 field specifies that the corners of the polygon should be drawn as circles
with the specified radius.
  </para>
</listitem>
</itemizedlist>

<para>
All points in an outline are specified relative to the origin of the enclosing
shape. Points in an outline may have negative values for the X and Y coordinate.
</para>


<para>
One outline (usually the first) is the primary outline; a keyboard display
application can generate a simpler but still accurate keyboard image by
displaying only the primary outlines for each shape. Non-rectangular keys must
include a rectangular <emphasis>
approximation</emphasis>
 as one of the outlines associated with the shape; the approximation is not
normally displayed but can be used by very simple keyboard display applications
to generate a recognizable but degraded image of the keyboard.
</para>


</sect1>
<sect1 id='sections'>
<title>Sections</title>

<para>
Each section has its own coordinate system — if a section is rotated, the
coordinates of any components within the section are interpreted relative to
the edges that were on the top and left before rotation. The components that
make up a section include:
</para>

<itemizedlist>
<listitem>
  <para>A list of <emphasis>
rows</emphasis>
. A row is a list of horizontally or vertically adjacent keys. Horizontal rows
parallel the (pre-rotation) top of the section and vertical rows parallel the
(pre-rotation) left of the section. All keys in a horizontal row share a common
top coordinate; all keys in a vertical row share a left coordinate.
  </para>
<para>
A key description consists of a key <emphasis>
name</emphasis>
, a <emphasis>
shape</emphasis>
, a key <emphasis>
color</emphasis>
, and a <emphasis>
gap</emphasis>
. The key <emphasis>
name</emphasis>
 should correspond to one of the keys named in the keyboard names description,
the <emphasis>
shape</emphasis>
 specifies the appearance of the key, and the key <emphasis>
color</emphasis>
 specifies the color of the key (not the label on the key). Keys are normally
drawn immediately adjacent to one another from left-to-right (or top-to-bottom)
within a row. The <emphasis>
gap</emphasis>
 field specifies the distance between a key and its predecessor.
  </para>
</listitem>
<listitem>
  <para>An optional list of doodads; any type of doodad can be enclosed within
a section. Position and angle of rotation are relative to the origin and angle
of rotation of the sections that contain them. Priority is relative to the
other components of the section, not to the keyboard as a whole.
  </para>
</listitem>
<listitem>
  <para>An optional list of <emphasis>
overlay keys</emphasis>
. Each overlay key definition indicates a key that can yield multiple scan
codes and consists of a field named <emphasis>
under</emphasis>
, which specifies the primary name of the key and a field named <emphasis>
over</emphasis>
, which specifies the name for the key when the overlay keycode is selected.
The key specified in <emphasis>
under</emphasis>
 must be a member of the section that contains the overlay key definition,
while the key specified in over must not.
  </para>
</listitem>
</itemizedlist>

</sect1>
<sect1 id='doodads'>
<title>Doodads</title>

<para>
Doodads can be global to the keyboard or part of a section. Doodads have
symbolic names of arbitrary length. The only doodad name whose interpretation
is specified by XKB is "Edges", which describes the outline of the entire
keyboard, if present.
</para>


<para>
All doodads report their origin in fields named <emphasis>
left</emphasis>
 and <emphasis>
top</emphasis>
. XKB supports five kinds of doodads:
</para>

<itemizedlist>
<listitem>
  <para>An <emphasis>
indicator doodad</emphasis>
 describes one of the physical keyboard indicators. Indicator doodads specify
the shape of the indicator, the indicator color when it is lit (<emphasis>
on_color</emphasis>
) and the indicator color when it is dark (<emphasis>
off_color</emphasis>
).
  </para>
</listitem>
<listitem>
  <para>An <emphasis>
outline doodad</emphasis>
 describes some aspect of the keyboard to be drawn as one or more hollow,
closed polygons. Outline doodads specify the shape, color, and angle of
rotation about the doodad origin at which they should be drawn.
  </para>
</listitem>
<listitem>
  <para>A <emphasis>
solid doodad</emphasis>
 describes some aspect of the keyboard to be drawn as one or more filled
polygons. Solid doodads specify the shape, color and angle of rotation about
the doodad origin at which they should be drawn.
  </para>
</listitem>
<listitem>
  <para>A <emphasis>
text doodad</emphasis>
 describes a text label somewhere on the keyboard. Text doodads specify the
label string, the font and color to use when drawing the label, and the angle
of rotation of the doodad about its origin.
  </para>
</listitem>
<listitem>
  <para>A <emphasis>
logo doodad</emphasis>
 is a catch-all, which describes some other visible element of the keyboard. A
logo doodad is essentially an outline doodad with an additional symbolic name
that describes the element to be drawn.
  </para>
  <para>
If a keyboard display program recognizes the symbolic name, it can draw
something appropriate within the bounding region of the shape specified in the
doodad. If the symbolic name does not describe a recognizable image, it should
draw an outline using the specified shape, outline, and angle of rotation.
  </para>
  <para>
The XKB extension does not specify the interpretation of logo names.
  </para>
</listitem>
</itemizedlist>

</sect1>
<sect1 id='keyboard_geometry_example'>
<title>Keyboard Geometry Example</title>

<para>
Consider the following example keyboard:
</para>

<mediaobject>
  <imageobject>
    <imagedata format="SVG" fileref="XKBproto-11.svg"/>
  </imageobject>
</mediaobject>


<para>
This keyboard has six sections: The left and right function sections (at the
very top) each have one horizontal row with eight keys. The left and right
alphanumeric sections (the large sections in the middle) each have six vertical
rows, with four or five keys in each row. The left and right editing sections
each have three vertical rows with one to three keys per row; the left editing
section is rotated 20° clockwise about its origin while the right editing
section is rotated 20° counterclockwise.
</para>


<para>
This keyboard has four global doodads: Three small, round indicators and a
rectangular logo. The program which generated this image did not recognize the
logo, so it displays an outline with an appropriate shape in its place.
</para>


<para>
This keyboard has seven shapes: All of the keys in the two function sections
use the "FKEY" shape. Most of the keys in the alphanumeric sections, as well as
four of the keys in each of the editing sections use the "NORM" shape. The keys
in the first column of the left alphanumeric section and the last column of the
right alphanumeric section all use the "WIDE" shape. Two keys in each of the
editing sections use the "TALL" shape. The "LED" shape describes the three
small, round indicators between the function and alphabetic sections. The
"LOGO" shape describes the keyboard logo, and the "EDGE" shape describes the
outline of the keyboard as a whole.
</para>


<para>
The keyboard itself is white, as are all of the keys except for the eight keys
that make up the home row, which use the "grey20" color. It isn’t really
visible in this picture, but the three indicators have an "on" color of "green"
and are "green30" when they are turned off. The keys in the alphanumeric and
editing sections all have a (vertical) gap of 0.5mm; the keys in the two
function sections have a (horizontal) gap of 3mm.
</para>


<para>
Many of the keys in the right alphanumeric section, and the rightmost key in
the right editing section are drawn with two names in this image. Those are
overlay keys; the bottom key name is the normal name while the overlay name is
printed at the top. For example, the right editing section has a single overlay
key entry, which specifies an <emphasis>
under</emphasis>
 name of <emphasis>
&lt;SPCE&gt;</emphasis>
 and an <emphasis>
over</emphasis>
 name of <emphasis>
&lt;KP0&gt;</emphasis>
, which indicates that the key in question is usually the shift key, but can
behave like the <emphasis>
0</emphasis>
 key on the numeric keypad when an overlay is active.
</para>
</sect1>
</chapter>