Terminology

Term	Meaning
Scancode	Value representing a physical key received from the RDP client. See [MS-RDPBCGR]. Essentially a 9 bit value.
Keycode	Value used by X11 to represent a physical key. This has essentially the same semantics as an RDP scancode. In the range 8-255
KeySym	Encoding of a symbol engraved into a key (e.g. XK_percent for a percent sign
Keyboard mapping table	A file in /etc/xrdp which maps keycodes to KeySyms and Unicode characters

Lookup process

The current process, ignoring modifiers, works as follows:-

1. An RDP scancode is received from the client.
2. This passes through an xrdp-specific lookup table to generate an keycode.
3. The keycode is further processed as follows:-
   1. [Login screen] The keycode is looked up in the keyboard mapping table to get a character for the keycode
   2. [VNC backend] The keycode is looked up in the keyboard mapping table to get a KeySym. This is used to inject an X Event into Xvnc.
   3. [Xorg backend] The RDP scancode is passed to xorgxrdp which performs its own translation. The keyboard mapping table is not used.

3c will be considered in later versions of this document.

Keycode

The translation from scancode to keycode seems a bit pointless based on the above description. Why go through an intermediate value? The answer is that somehow we need to produce the keyboard mapping tables. Each keyboard mapping table is produced by running a program called genkeymap. This uses the Xlib XLookupString() call to convert all 247 keycodes into KeySyms and characters. Before the program is run, the setxkbmap program is used to set a particular keyboard model and layout.

This process works fine provided the X11 keycodes used by the X server match the table embedded into xrdp. However, there is no official standard in this area.

When xrdp was created, the predominant X server used was RealVNC. At the time that used its own particular mapping. Since then, a lot has changed:-

1. Linux (and FreeBSD) have standardised on keycodes produced by the evdev driver.
2. The predominant VNC server is now RealVNC, which also uses evdev keycodes.

Keycode values (xrdp v0.10.x and earlier)

The following table maps scan codes to keycodes for xrdp v0.10.x and earlier. The keycodes exactly correspond to the values listed in keyboard ini files:

Scancode	Keycode	Scancode	Keycode	Scancode	Keycode	Scancode	Keycode
01	9	25	45	49	81	70	120
02	10	26	46	4A	82	71	121
03	11	27	47	4B	83	72	122
04	12	28	48	4C	84	73	123
05	13	29	49	4D	85	74	124
06	14	2A	50	4E	86	75	125
07	15	2B	51	4F	87	76	126
08	16	2C	52	50	88	77	127
09	17	2D	53	51	89	78	128
0A	18	2E	54	52	90	79	129
0B	19	2F	55	53	91	7A	130
0C	20	30	56	54	92	7B	131
0D	21	31	57	55	93	7C	132
0E	22	32	58	56	94	7D	133
0F	23	33	59	57	95	7E	134
10	24	34	60	58	96	7F	135
11	25	35	61	59	97	E0_1C	108
12	26	36	62	5A	98	E0_1D	109
13	27	37	63	5E	102	E0_35	112
14	28	38	64	5F	103	E0_37	111
15	29	39	65	60	104	E0_38	113
16	30	3A	66	61	105	E0_47	97
17	31	3B	67	62	106	E0_48	98
18	32	3C	68	63	107	E0_49	99
19	33	3D	69	64	108	E0_4B	100
1A	34	3E	70	65	109	E0_4D	102
1B	35	3F	71	66	110	E0_4F	103
1C	36	40	72	67	111	E0_50	104
1D	37	41	73	68	112	E0_51	105
1E	38	42	74	69	113	E0_52	106
1F	39	43	75	6A	114	E0_53	107
20	40	44	76	6B	115	E0_5B	115
21	41	45	77	6C	116	E0_5C	116
22	42	46	78	6D	117	E0_5D	117
23	43	47	79	6E	118
24	44	48	80	6F	119

Keycode values (xrdp v0.11.x)

X11 keycodes now used by xrdp are normally the evdev ones, but base can also be selected if required.