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I am using a generic usb keyboard, Linux 2.6.27 with gnome desktop, gnome-terminal and bash shell. I am interested to know what happens in the software. How are special characters from my keyboard interpreted with some encoding to characters and where do the character pictures come from?
The Linux input layer with the USB drivers gets scancodes (basically ‘KEY 1 DOWN’ ‘KEY 1 UP’) from the keyboard.
X uses its keymap to convert scancodes into keycodes and X input events.
The GTK input method converts the sequence of input events into composed unicode characters.
Gnome-terminal encodes these in UTF-8 for the shell.
The Shell doesn’t care. it just knows that it’s dealing with a multibyte encoding.
The shell echoes multibyte-encoded text back through the TTY.
Gnome-terminal decodes the incoming text and determines unicode code points.
Gnome-terminal draws characters using GTK+ facilities.
GTK+ uses Pango to render the text, and calls the X library to draw the pixels to the screen.
The X server draws characters into the screen buffer and the video card displays them.
Here is my attempt at a diagram:
alt text http://osoft.us/system_layers.png