README.md: Finish the documentation

Fixes #2.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

README.md

@@ -11,31 +11,133 @@
 
 A common base for plugins that want to provide themes, or theme-related
 capabilities, using a 15+1 color palette. In other words, this is for plugin
-authors primarily.
+authors primarily. The primary aim of the plugin is to provide not only a common
+palette, but tools that make it easier to use it too.
 
 ## Using the plugin
 
-TODO
+To use the plugin, one needs to do a bit more than include the header, and tell
+the firmware to use it. Itself being a mere building block, to use it to its
+full extent, we need to create our own plugin on top of it.
 
 ```c++
 #include <Kaleidoscope.h>
 #include <Kaleidoscope-EEPROM-Settings.h>
 #include <Kaleidoscope-LED-Palette-Theme.h>
+#include <Kaleidoscope-Focus.h>
+
+namespace example {
+
+class TestLEDMode : public LEDMode {
+ public:
+  TestLEDMode() {}
+  void begin(void) final;
+  void update(void) final;
+
+  static bool focusHook(const char *command);
+
+ private:
+  static uint16_t map_base_;
+};
+
+uint16_t TestLEDMode::map_base_;
+
+void
+TestLEDMode::begin(void) {
+  LEDMode::begin();
+  map_base_ = LEDPaletteTheme.reserveThemes(1);
+}
+
+void
+TestLEDMode::update(void) {
+  LEDPaletteTheme.updateHandler(map_base_, 0);
+}
+
+bool
+TestLEDMode::focusHook(const char *command) {
+  return LEDPaletteTheme.themeFocusHandler(command, PSTR("testLedMode.map"), map_base_, 1);
+}
+
+}
+
+example::TestLEDMode TestLEDMode;
 
 void setup() {
-  USE_PLUGINS(&EEPROMSettings, &LEDPaletteTheme);
+  Serial.begin(9600);
+
+  USE_PLUGINS(&Focus, &LEDPaletteTheme, &TestLEDMode, &EEPROMSettings);
 
   Kaleidoscope.setup();
 
-  // TODO
+  EEPROMSettings.seal();
+  TestLEDMode.activate();
+
+  Focus.addHook(FOCUS_HOOK_LEDPALETTETHEME);
+  Focus.addHook(FOCUS_HOOK(TestLEDMode.focusHook, "testLEDMode.map"));
 }
 ```
 
-## Plugin methods
+This is a simple extension, where it provides a `testLEDMode.map` Focus command,
+with which one can set the theme which will be saved to EEPROM.
 
-The plugin provides the `LEDPaletteTheme` object, which has the following methods:
+## Plugin methods
 
-**TODO**
+The plugin provides the `LEDPaletteTheme` object, which has the following methods and properties:
+
+### `.reserveThemes(max_themes)`
+
+> Reserve space in EEPROM for `max_themes`. Each key on a theme uses half a byte
+> of space. The function returns the `theme_base` to be used with the rest of
+> the methods.
+>
+> The `theme_base` is a pointer into the EEPROM where the theme storage starts.
+
+### `.updateHandler(theme_base, theme)`
+
+> A helper we can call in our plugin's `.update()` method: given an EEPROM
+> location (`theme_base`), and a `theme` index, it will update the keyboard with
+> the colors of the specified theme.
+>
+> The `theme` argument can be any index between zero and `max_themes`. How the
+> plugin decides which theme to display depends entirely on the plugin.
+
+### `.themeFocusHandler(command, expected_command, theme_base, max_themes)`
+
+> To be used in a custom `Focus` handler: handles the `expected_command` Focus
+> command, and provides a way to query and update the themes supported by the
+> plugin.
+>
+> When queried, it will list the color indexes. When used as a setter, it
+> expects one index per key.
+>
+> The palette can be set via the `palette` focus command, implemented by the
+> `FOCUS_HOOK_LEDPALETTETHEME` hook explained below.
+
+### `.transparent_index`
+
+> The plugin supports transparent colors too: by default, the last color (index
+> 15) is treated as transparent. If a pixel is found to be transparent,
+> `.updateHandler` will not change its color, but leave it as is. This way one
+> can create layers of themes, if so desired.
+>
+> This property can be set to a number between 0 and 15 to make that index
+> transparent, or to a number higher than 15 to disable transparency support,
+> and gain another color on the palette.
+
+## Focus commands
+
+The plugin provides a single `Focus` hook, `FOCUS_HOOK_LEDPALETTETHEME`,
+implementing the following command:
+
+### `palette`
+
+> Without arguments, prints the palette: RGB values for all 16 colors.
+>
+> With arguments, updates the palette with new colors. One does not need to give
+> the full palette, the plugin will process as many arguments as available, and
+> ignore anything past the last index. It expects colors to have all three
+> components specified, or none at all. Thus, partial palette updates are
+> possible, but only on the color level, not at component level.
 
 ## Dependencies