[retro-gtk] keyboard-key: Simplify and document key convertion

[Adrien Plazas <aplazas src gnome org>]

commit fcfd3c8a8fc3d525139e334cf0d37c0beebfe8ea
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Fri May 4 09:27:11 2018 +0200

    keyboard-key: Simplify and document key convertion
    
    Simplify a bit keyboard convertion to avoid most usage of magic numbers
    and better document the reasoning behind each convertion.

 retro-gtk/retro-keyboard-key.c | 66 ++++++++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 25 deletions(-)
---
diff --git a/retro-gtk/retro-keyboard-key.c b/retro-gtk/retro-keyboard-key.c
index bdaa9f8..e43056b 100644
--- a/retro-gtk/retro-keyboard-key.c
+++ b/retro-gtk/retro-keyboard-key.c
@@ -29,31 +29,47 @@ retro_keyboard_modifier_key_converter (guint           keyval,
 RetroKeyboardKey
 retro_keyboard_key_converter (guint keyval)
 {
-  guint key;
-
-  // Common keys (0x0020 to 0x00fe)
-  if (keyval < 0x80) {
-    key = (0x7f & keyval);
-
-    // If the key is uppercase, turn it lower case
-    if (key >= 'A' && key <= 'Z')
-      return key + 0x20;
-
-    return key;
-  }
-
-  // Function keys
-  key = keyval - GDK_KEY_F1;
-  if (key < 15)
-    return RETRO_KEYBOARD_KEY_F1 + key;
-
-  // Keypad digits
-  key = keyval - GDK_KEY_KP_0;
-  if (key < 10)
-    return RETRO_KEYBOARD_KEY_KP0 + key;
-
-  // Various keys
-  // Missing keys: MODE, COMPOSE, POWER
+  /*
+   * US-ASCII codes
+   *
+   * Both GDK_KEY_* and RETRO_KEYBOARD_KEY_* start with the US-ASCII codes,
+   * implementing common letters, digits and symbols.
+   *
+   * If the key is uppercase, turn it lower case as Libretro doesn't make a
+   * distinction between these.
+   */
+  if (keyval < 0x80)
+    return (keyval >= GDK_KEY_A && keyval <= GDK_KEY_Z) ?
+      keyval + (GDK_KEY_a - GDK_KEY_A) : keyval;
+
+  /*
+   * Function keys
+   *
+   * Both GDK_KEY_F* and RETRO_KEYBOARD_KEY_F* implement function keys 1—15 in a
+   * consecutive manner. GDK_KEY_F* actually implements more function keys but
+   * RETRO_KEYBOARD_KEY_F* doesn't.
+   */
+  if (keyval >= GDK_KEY_F1 && keyval <= GDK_KEY_F15)
+    return RETRO_KEYBOARD_KEY_F1 + (keyval - GDK_KEY_F1);
+
+  /*
+   * Keypad digits
+   *
+   * Both GDK_KEY_KP_* and RETRO_KEYBOARD_KEY_KP* implement keypad digits 0–9 in
+   * a consecutive manner.
+   */
+  if (keyval >= GDK_KEY_KP_0 && keyval <= GDK_KEY_KP_9)
+    return RETRO_KEYBOARD_KEY_KP0 + (keyval - GDK_KEY_KP_0);
+
+  /*
+   * Various keys
+   *
+   * FIXME: The following keys are unimplemented because I couldn't find the
+   * right GDK_KEY_* equivalent:
+   * - RETRO_KEYBOARD_KEY_MODE
+   * - RETRO_KEYBOARD_KEY_COMPOSE
+   * - RETRO_KEYBOARD_KEY_POWER
+   */
   switch (keyval) {
   case GDK_KEY_BackSpace:
     return RETRO_KEYBOARD_KEY_BACKSPACE;