Replace the Docbook version of pictogram spec with one using reStructuredText.

The idea was to write on Docbook to be able to copy and paste the spec into
the Developer's Guide. However, writing a quickly changing document in Docbook
turned out to be complicated. RST is faster to update and can be converted
into nice HTML using docutils.
This commit is contained in:
mmdolze
2012-09-01 22:25:25 +00:00
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<?xml version='1.0'?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<article>
<title>Pictogram Specification For LCDproc</title>
<articleinfo>
<author>
<firstname>Markus</firstname>
<surname>Dolze</surname>
<email>bsdfan@nurfuerspam.de</email>
</author>
<releaseinfo>Prelimary specification</releaseinfo>
</articleinfo>
<sect1><title>Introduction</title>
<para>In addition to alphanumeric characters represented by segments or
pixels, LCD/VFD displays are often capable to show additional pictograms,
mostly arranged around the alphanumeric display part.</para>
<para>These pictograms can be switched on or off, or by changing their
appearance as seen for volume settings.</para>
<para>LCDproc comes with icons that are integrated into the alphanumeric
display part, but is unaware of pictograms as described above.</para>
<para>One current workaround is to use the output() function to pass values to
a driver that uses these values to set pictograms. The downside is that any
application which wants to make use of these pictograms need to know the
exact type of display driver used and how that drivers handles values to the
output() function.</para>
<para>This document aims to specify client language and driver API
extensions address pictograms in a manner not specific to certain drivers.
</para>
<note><para>The common term for pictograms is indeed icons, but to
distinguish the feature from LCDproc's already existing icon feature the
term <termdef>pictogram</termdef> has been chosen.</para></note>
</sect1>
<sect1><title>Client language</title>
<para>
There are two language commands that can be called by the client:
pictograms_get and pictogram_set.
</para>
<variablelist>
<varlistentry>
<term>
<command>pictograms_get</command>
</term>
<listitem>
<para>This command may be called by a client to get a list of
available pictograms. If pictograms are not support by the
particular version of LCDd, it will respond with an error
message (huh? unknown command).</para>
<note>
<para>Clients should either check the version number returned as
response to the 'hello' command or the response to
'pictograms_get' to check if LCDd supports pictograms before
calling 'pictogram_set' (see below).</para>
</note>
<para>
The response will be a string in the format:
</para>
<para>
<computeroutput>pictograms <replaceable>pictogram list</replaceable>...</computeroutput>
</para>
<para>
The pictogram list will be a sequence of pictogram
definitions separated by a space character. Each pictogram
definition consists of up to four fields separated by a colon.
<variablelist>
<varlistentry>
<term>
<computeroutput><replaceable>Name</replaceable></computeroutput>
</term>
<listitem><para>
The text representation of the pictogram name.
</para></listitem>
</varlistentry>
<varlistentry>
<term>
<computeroutput><replaceable>Type</replaceable></computeroutput>
</term>
<listitem><para>
The type of the pictogram: 'n' for numerical pictograms
and 'b' for boolean type pictograms.
</para></listitem>
</varlistentry>
<varlistentry>
<term>
<computeroutput><replaceable>Group ID</replaceable></computeroutput>
</term>
<listitem>
<para>The Group ID is optional and if present is a number greater than zero
that models the driver's idea of a several pictograms that form a group. This
may e.g. be used for media source pictograms.</para>
<note>
<para>The group ID is only informational for the client and is not used
within LCDd. The driver however may make use of groups internally.</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term>
<computeroutput><replaceable>Group type</replaceable></computeroutput>
</term>
<listitem><para>
</para></listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<command>pictogram_set
<option><replaceable>pictogram</replaceable>:<replaceable>value</replaceable></option>
</command>
</term>
<listitem>
<para>
</para>
</listitem>
</varlistentry>
</variablelist>
</sect1>
<sect1><title>Driver API</title>
<para>The driver API (struct lcd_logical_driver in <filename>lcd.h</filename>)
will be extended with a new function to process pictograms:</para>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>(*set_pictogram)</function></funcdef>
<paramdef>unsigned int <parameter>pictogramID</parameter></paramdef>
<paramdef>int <parameter>value</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>
The pictogram function. The first parameter will be a pictogram
number (ID) and the second parameter will be its value. The function
will return 0 (zero) if the pictogram is understood by the driver
and -1 (minus one) if it is not supported.
</para>
<note>
<para>Their will be no alternative implementation in LCDd core if a
driver does not understand a pictogram (like it is done for icons).
</para>
<para>This function will never be called with multiple pictogram IDs
combined into one. It will be called for each pictogram to be set /
cleared. If a driver wishes to reduce communication with the
hardware it may implement some kind of cache and write the changes
on a call to flush().</para>
</note>
<para>
The pictogram ID is defined in the file called <filename>
lcd_pictograms.h</filename> as an enumerated type. It will have a
symbolic name prefixed with <termdef>PICT_</termdef>. Drivers MUST
NOT address pictograms by their ID number but only by their symbolic
name (e.g. within a switch statement) as the numbers are subject to
change.
</para>
<para>
There will be two types of pictograms:
<variablelist>
<varlistentry>
<term>
Boolean type pictograms
</term>
<listitem><para>
This type of pictograms can be turned on (visible) or off (not visible).
Valid values are 0 (zero) which means off, or 1 (one) which means on.
</para></listitem>
</varlistentry>
<varlistentry>
<term>
Numeric type pictograms
</term>
<listitem><para>
This type of pictograms will change its appearance
according to the value assigned, e.g. a graph or WLAN
strength indicator. Valid values are within the range
0-1000. A value of 0 (zero) turns the pictogram off.
</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>
There will be one reserved pictogram ID (symbolic name e.g.
PICT_ALL) which will be of boolean type and means that all
pictograms the driver supports shall be turned off or on.
</para>
<note>
<para>There are currently several options discussed on the mailing
list, given here for reference:</para>
<itemizedlist>
<listitem><para>
There may be a third level for boolean type pictograms
which does highlight it (e.g. make it more brighter or
use a different color).
</para></listitem>
<listitem><para>
Values for numeric type may be negative. This allows
pictograms to have an opposite direction, e.g. graphs
growing from right-to-left instead of from left-to-right.
</para></listitem>
<listitem><para>
Drivers may define their local set of pictogram ID and
assorted client language names.
</para></listitem>
<listitem><para>
Pictograms may be implemented as widgets. In this case
LCDd core will keep track of its value.
</para></listitem>
<listitem><para>
...
</para></listitem>
</itemizedlist>
</note>
</sect1>
<sect1><title>Internal implementation</title>
<para>This section should talk about processing of client messages, mapping
of pictogram names to pictogram IDs.</para>
</sect1>
</article>
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===================================
Pictogram Specification For LCDproc
===================================
:Author: Markus Dolze
:Contact: <bsdfan@nurfuerspam.de>
.. contents::
Introduction
============
In addition to alphanumeric characters represented by segments or pixels,
LCD/VFD displays are often capable to show additional pictograms, mostly
arranged around the alphanumeric display part.
These pictograms can be switched on or off, or by changing their appearance
as seen for volume settings.
LCDproc comes with icons that are integrated into the alphanumeric display
part, but is unaware of pictograms as described above.
One current workaround is to use the output() function to pass values to a
driver that uses these values to set pictograms. The downside is that any
application which wants to make use of these pictograms need to know the
exact type of display driver used and how that drivers handles values to the
output() function.
This document aims to specify client language and driver API extensions
address pictograms in a manner not specific to certain drivers.
.. note::
The common term for pictograms is indeed icons, but to distinguish the
feature from LCDproc's already existing icon feature the term
[Definition: pictogram] has been chosen.
Client language
===============
This section should talk about the client language.
Driver API
==========
The driver API (struct lcd_logical_driver in lcd.h) will be extended with a
new function to process pictograms:
.. code:: c
int (*set_pictogram)(unsigned int pictogramID, int value);
The pictogram function. The first parameter will be a pictogram number (ID)
and the second parameter will be its value. The function will return 0
(zero) if the pictogram is understood by the driver and -1 (minus one) if it
is not supported.
.. note::
Their will be no alternative implementation in LCDd core if a driver does
not understand a pictogram (like it is done for icons).
This function will never be called with multiple pictogram IDs combined
into one. It will be called for each pictogram to be set / cleared. If a
driver wishes to reduce communication with the hardware it may implement
some kind of cache and write the changes on a call to flush().
The pictogram ID is defined in the file called lcd_pictograms.h as an
enumerated type. It will have a symbolic name prefixed with [Definition:
PICT\_]. Drivers MUST NOT address pictograms by their ID number but only by
their symbolic name (e.g. within a switch statement) as the numbers are
subject to change.
There will be two types of pictograms:
Boolean type pictograms
This type of pictograms can be turned on (visible) or off (not visible).
Valid values are 0 (zero) which means off, or 1 (one) which means on.
Numeric type pictograms
This type of pictograms will change its appearance according to the value
assigned, e.g. a graph or WLAN strength indicator. Valid values are within
the range 0-1000. A value of 0 (zero) turns the pictogram off.
There will be one reserved pictogram ID (symbolic name e.g. PICT_ALL) which
will be of boolean type and means that all pictograms the driver supports
shall be turned off or on.
.. note:: There are currently several options discussed on the mailing list,
given here for reference:
* There may be a third level for boolean type pictograms which does
highlight it (e.g. make it more brighter or use a different color).
* Values for numeric type may be negative. This allows pictograms to have
an opposite direction, e.g. graphs growing from right-to-left instead of
from left-to-right.
* Drivers may define their local set of pictogram ID and assorted client
language names.
* Pictograms may be implemented as widgets. In this case LCDd core will
keep track of its value.
Internal implementation
=======================
This section should talk about processing of client messages, mapping of
pictogram names to pictogram IDs.