From 602c049b39ce7f881e5c13b76d5419b106c50c86 Mon Sep 17 00:00:00 2001
From: Kjell Ericson <kjell@haxx.se>
Date: Fri, 10 Jan 2003 11:07:14 +0000
Subject: Description of how Rocklatin works and looks like.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@3060 a1c6a512-1295-4272-9138-f99709370657
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+#define _PAGE_ Rocklatin
+#include "head.t"
+
+<h1>Rocklatin1</h1>
+
+Only for developers...
+
+<h2>Background</h2>
+The Archos player comes in two models. One with old LCD and one with new LCD.
+(Differences can be seen below). You can't find any difference more than the
+LCD, therefor we run the same code on both models. The original software
+contains two different mappings from ASCII-character to hardware-LCD. Because
+some characters doesn't exist in both hardwares all national characters
+are left out in both hardware.
+<p>The old LCD can have 4 software defined characters, and the new LCD can
+have 8 software defined characters.
+<table border=1><tr>
+<td>HW layout of old LCD:<br><img width=272 height=272 src="lcd_old_hw.gif"></td>
+<td>HW layout of new LCD:<br><img width=272 height=272 src="lcd_new_hw.gif"></td>
+</tr></table>
+
+<h2>What is Rocklatin1</h2>
+Rocklatin1 is based on Winlatin1 (which is identical to Latin1 but some
+extra characters). All characters presented in any HW-LCD (i.e. old LCD)
+is mapped in Rocklatin1 and some extra characters we find good to use.
+
+<table border=1><tr>
+<td>Rocklatin1 of old LCD:<br><img width=272 height=272 src="lcd_old.gif"></td>
+<td>Rocklatin1 of new LCD:<br><img width=272 height=272 src="lcd_new.gif"></td>
+</tr></table>
+The red characters are characters not defined in the HW-LCD. These characters
+are mapped by the software to a software defined character (0-4/8) whenever 
+they are used.
+
+<h2>But what if...</h2>
+...all software defined characters are taken?<br>
+Well, then a substitute character will be used for that character.
+
+<table border=1><tr>
+<td>Substitute of old LCD:<br><img width=272 height=272 src="lcd_old_subst.gif"></td>
+<td>Substitute of new LCD:<br><img width=272 height=272 src="lcd_new_subst.gif"></td>
+</tr></table>
+The red characters shows where a substitution is made.
+
+<p>
+All Rocklatin1 characters between 0x00 and 0x1f are hardcoded to be prioritized.
+That means that if a national character is displayed at LCD and an icon
+(0x18-0x1f) is to be shown, the character with highest Rocklatin1 value will
+be switched to a substitute character.
+
+<h2>Accessing hardware</h2>
+The Rockbox software can access a HW-LCD-character by doing a lcd_putc(0x100-0x1ff). That would of course make it 100% hardware depended (=not good).
+<p>
+The Rockbox software can also define 23 own patterns, even though hardware only
+allows 4 or 8. The software should of course not try to display more than 4
+or 8 of such characters. This code example shows how to define a pattern:
+<pre>
+{
+  unsigned char pattern[]={ 0x0a, 0x00, 0x00, 0x0c,
+                            0x04, 0x04, 0x0e};
+  unsigned char handle;
+
+  handle=lcd_get_locked_pattern();
+  lcd_define_pattern(handle, pattern);
+
+  lcd_putc(x, y, handle);
+
+  ...
+
+  lcd_unlock_pattern(handle);
+}
+</pre>
+The handle is very likely to be between 0x01 to 0x17, which in software will
+be handled as a prioritized character (even higher than the icons).
+
+<h2>Some notes</h2>
+<ul>
+<li>Displaying the same rocklatin-mapped-character many times at the LCD
+only occupies one HW-LCD-mapped character.
+<li>If a substitute character is used, the "should-be" character will never
+be shown (no flickering screen) until the character is moved or scrolled.
+<li>Characters already displayed are only substituted if a prioritized
+character is to be displayed.
+<li>The software maps the characters circular in order to minimize the
+likelyhood to remap the same character very often.
+<li>The gifs above is generated with the tool "generate_rocklatin".
+<li>Rocklatin character 0x92 is defined as the "cursor" character.
+<li>Rocklatin character 0x93-0x95 is only used for substitution (a substitute
+character must be a Rocklatin character).
+<li>Implementation and design by Kjell Ericson and Mats Lidell (for questions).
+<li>Rocklatin1 is based on Winlatin1 because the old LCD happened to have 7
+of the Winlatin1-extra characters (no need to remap/remove those).
+<li>If you find any characters identical in old and new HW-LCD that aren't
+mapped (and really are useful) you can tell us.
+</ul>
+
+#include "foot.t"
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