dos-vga-arena-shooter-game/system/keyboard.c

#include <dos.h>
#include <conio.h>

#include "keyboard.h"

unsigned char keystateBits[16];
struct KeyboardKeydownState keyboardKeydownState;

void far (interrupt *int9Save)();

void populateKeyboardKeydownState() {
  keyboardKeydownState.KEY_W = keystateBits[2] & 0x02;
  keyboardKeydownState.KEY_A = keystateBits[3] & 0x40;
  keyboardKeydownState.KEY_S = keystateBits[3] & 0x80;
  keyboardKeydownState.KEY_D = keystateBits[4] & 0x01;
  keyboardKeydownState.KEY_ESC = keystateBits[0] & 0x02;
}

void far interrupt keyboardHandler(void) {
  unsigned char rawcode, scancode, ksbByte, temp;
  unsigned char mask = 1;

  _disable();

  rawcode = inp(0x60);

  scancode = rawcode & 0x7f;
  mask = 1 << (scancode & 0x07);
  ksbByte = scancode >> 3;

  // https://github.com/id-Software/wolf3d/blob/05167784ef009d0d0daefe8d012b027f39dc8541/WOLFSRC/ID_IN.C#L152-L154
  outp(0x61, (temp = inp(0x61)) | 0x80);
  outp(0x61, temp);

  /* break */
  if (rawcode & 0x80) {
      mask = 0xff - mask;
      keystateBits[ksbByte] &= mask;
  /* make */
  } else {
      keystateBits[ksbByte] |= mask;
  }

  // acknowledge we're done with the interrupt
  outp(0x20, 0x20);

  _enable();
}

void installKeyboardHandler() {
  int9Save = _dos_getvect(9);
  _dos_setvect(9, keyboardHandler);
}

void uninstallKeyboardHandler() {
  _dos_setvect(9, int9Save);
}