Keyboard Input



Basics

Using FB's built-in functionality, there are four ways of getting keyboard input:

  • inkey() returns a string containing an ASCII char corresponding to the key pressed by the user, or a 2-byte FB extended keycode for some special keys, such as the Arrow keys or Page Up/Down. It works pretty much like it did in QB.

  • getkey() returns the same information as inkey(), but in form of an integer instead of a string. inkey() and getkey() belong together: They use the same code and they are located in the same modules.


  • screenevent() returns key presses in form of EVENT_KEY_PRESS events (and others for key release or repeat). It returns the FB scancode in the EVENT.scancode field, and the ASCII char value or 0 in the EVENT.ascii field. EVENT.ascii does not use FB extended keycodes; the EVENT.scancode field can be checked instead in order to handle extended keys.

"scancode" refers to the SC_* #defines which are more or less matching the DOS keyboard scancodes. The values are not made up, they themselves correspond to certain ASCII chars, for example: SC_HOME = asc( "G" ) = &h47. They're also the same values that you get under DOS/DJGPP or from the Linux kernel as part of extended key code sequences. Besides their use in multikey() or screenevent(), scancodes are used in various places internally, for example when translating between different kinds of key codes, as an easy-to-use and portable representation of keycodes.

"key" refers to an ASCII char, or a 2-byte extended keycode string for other keys as returned by inkey(). The rtlib has several KEY_* #defines for the available 2-byte extended keycodes, in form of integers. These are used internally and also match the values returned by getkey().

FB's 2-byte extended keycodes consist of a &hFF byte followed by a byte containing the SC_* scancode value corresponding to the keypress. Checking for SC_HOME returned by inkey() could look like:
if( inkey( ) = chr( 255 ) + "G" ) then ...
Checking for SC_HOME returned by getkey():
if( getkey() = &h47FF ) then ...
if( getkey() = ((SC_HOME shl 8) or &hFF) ) then ...

inkey(), getkey() and multikey() use wrapper functions that call ...
  • the console-mode versions fb_ConsoleInkey(), fb_ConsoleGetkey(), fb_ConsoleMultikey() by default,
  • or the gfxlib versions fb_GfxInkey(), fb_GfxGetkey(), fb_GfxMultikey() if a graphics SCREEN is active,
by using function pointer hooks.

rtlib

The rtlib has separate console-mode implementations of the above functions, for each platform:




gfxlib2

In the gfxlib, fb_GfxInkey() and fb_GfxGetkey() use one key buffer (same code on all platforms), to which the different/platform-specific gfx drivers post keys to. Similar to that, there is a single key state table for fb_GfxMultikey(), and it is also updated by the gfx drivers. Whether or not the gfx drivers actually do post keys or update key states is up to them though.





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