View source for Debouncing Multiple-Keypress PRGM GetKey

== Synopsis ==
The below code is not a single function, but rather a group of functions for fulfilling a single purpose: providing key debouncing and multi-keypress detection to the PRGM GetKey function.  The needed function and variable declarations are as follows:

=== Definition ===

  const unsigned short* keyboard_register = (unsigned short*)0xA44B0000;
  unsigned short lastkey[8];
  unsigned short holdkey[8];
  
  void keyupdate(void) {
     memcpy(holdkey, lastkey, sizeof(unsigned short)*8);
     memcpy(lastkey, keyboard_register, sizeof(unsigned short)*8);
  }
  int keydownlast(int basic_keycode) {
     int row, col, word, bit; 
     row = basic_keycode%10; 
     col = basic_keycode/10-1; 
     word = row>>1; 
     bit = col + 8*(row&1); 
     return (0 != (lastkey[word] & 1<<bit)); 
  }
  int keydownhold(int basic_keycode) {
     int row, col, word, bit; 
     row = basic_keycode%10; 
     col = basic_keycode/10-1; 
     word = row>>1; 
     bit = col + 8*(row&1); 
     return (0 != (holdkey[word] & 1<<bit)); 
  }


These functions are used to check the current state of a key in the key array during the current loop runthrough, or check the value from the last loop.  These use the KEY_PRGM_<key> key codes, and should be used in something like a game loop to provide clean debouncing.  Here is an example of these functions at work in an example game loop:

  while(running) {
    keyupdate(); // update both key arrays
  
    ...
  
    // checking to see if the up key has been held down for a while
    if(keydownlast(KEY_PRGM_UP) && keydownhold(KEY_PRGM_UP))
  
    // checking to see if the up key has not been held down for a while
    if(!keydownlast(KEY_PRGM_UP) && !keydownhold(KEY_PRGM_UP))
  
    // checking to see if the up key has just been pressed
    if(keydownlast(KEY_PRGM_UP) && !keydownhold(KEY_PRGM_UP))
  
    // checking to see if the up key has just been released
    if(!keydownlast(KEY_PRGM_UP) && keydownhold(KEY_PRGM_UP))
  }

=== Inputs ===
keyupdate: None

keydownlast: int (KEY_PRGM_<key> keycode)

keydownhold: int (KEY_PRGM_<key> keycode)

=== Outputs ===
keyupdate: None

keydownlast: 1 if key has been pressed during last keyupdate() call, 0 otherwise

keydownhold: 1 if key has been pressed two keyupdate() calls ago, 0 otherwise

== Comments ==
It's a bit more wordy to use than its simple PRGM GetKey sibling, but it's also very flexible and can even be used to check for pseudo keydown/keyup key events.  It also reads directly from keyboard hardware ports, so it's very fast and doesn't rely on the OS's control.
[[Category: Useful Routines]]