#include <stdio.h>
#include <i86.h>
#include <conio.h>
#include <dos.h>

extern void __cdecl enableUnchainedVGAMode();
extern void __cdecl enableTextMode();
extern void __cdecl fillScreen(int);
extern void __cdecl latchCopyCube(
  int offset,
  int writtenValue,
  int writeMode,
  int setResetRegister,
  int enableSetResetRegister
);
extern void __cdecl writeCube(
  int offset,
  int writeMode,
  int setResetRegister,
  int enableSetResetRegister
);
extern void __cdecl drawColorCube(
  char offset,
  int color
);

extern void far interrupt keyboardHandler();
extern char keyboardPressed;
extern char lastScancode;

char far *VGA = (char*)0xA0000;

#define PLANE_WIDTH (320 / 4)

void far (interrupt *int9Save)();

void populateExampleCube(void) {
  int y, x;

  outp(0x3c4, 0x02);

  for (x = 0; x < 16; ++x) {
    outp(0x3c5, 1 << (x % 4));
    for (y = 0; y < 16; ++y) {
      VGA[y * PLANE_WIDTH + x / 4] = y * 16 + x;
    }
  }
}

void forceReadVGA(char far *vga);
#pragma aux forceReadVGA = \
"mov bl,BYTE PTR [eax]" \
parm [ eax ] \
modify [ bl ];

int main(void) {
  char a;
  // activate unchained vga mode
  // place some data into video memory to be latch copied
  // show off the following
  // * latch copies with logical operators
  // * plane selection
  // * barrel shifting
  // * set/reset

  int9Save = _dos_getvect(9);
  _dos_setvect(9, keyboardHandler);

  enableUnchainedVGAMode();

  // set a very bright color as the last possible color to make
  // set/reset usage more visible
  outp(0x3c8, 255);
  outp(0x3c9, 63);
  outp(0x3c9, 63);
  outp(0x3c9, 63);

  fillScreen(0);

  populateExampleCube();

  latchCopyCube(80 * 20, 0, 0x00, 0, 0);
  latchCopyCube(80 * 20 + 5, 127, 0x00, 0, 0);
  latchCopyCube(80 * 20 + 10, 0, 0x08, 0, 0);
  latchCopyCube(80 * 20 + 15, 127, 0x08, 0, 0);
  latchCopyCube(80 * 20 + 20, 0, 0x10, 0, 0);
  latchCopyCube(80 * 20 + 25, 127, 0x10, 0, 0);
  latchCopyCube(80 * 20 + 30, 0, 0x18, 0, 0);
  latchCopyCube(80 * 20 + 35, 127, 0x18, 0, 0);
  latchCopyCube(80 * 20 + 40, 127, 0x10, 1, 3);

  latchCopyCube(80 * 40, 0, 0x18 + 0x04, 0, 0);
  latchCopyCube(80 * 40 + 5, 127, 0x18 + 0x04, 0, 0);

  latchCopyCube(80 * 40 + 10, 0, 0x10, 3, 3);
  latchCopyCube(80 * 40 + 15, 0, 0x10, 1, 3);
  latchCopyCube(80 * 40 + 20, 0, 0x10, 0, 3);

  writeCube(5, 0x00, 1, 3);
  writeCube(10, 0x00, 0, 3);
  writeCube(15, 0x00, 3, 0);

  outpw(0x3ce, 0x0000);
  outpw(0x3ce, 0x0001);
  outpw(0x3ce, 0x0002);
  outpw(0x3ce, 0x0003);
  /*
  outpw(0x3ce, 0x0005);
  */
  outpw(0x3ce, 0xff08);
  outpw(0x3c4, 0x0f02);
  /*
  outp(0x3ce, 0x08);
  outp(0x3cf, 0xff);
  */

  VGA[0] = 255;
  // read the above. if you're reading the value and doing nothing with it, watcom will optimize it out
  forceReadVGA(VGA);

  //outp(0x3cf, 0xff);
  // all from latches
  outpw(0x3ce, 0x0008);

  VGA[2] = 127;

  // all but the first bit from incoming data
  outpw(0x3ce, 0xfe08);

  VGA[4] = 2;

  a = VGA[4];

  /*
  outp(0x3cf, 0x00);

  VGA[410] = 0;
  */

  while (keyboardPressed == 0);

  _dos_setvect(9, int9Save);

  enableTextMode();

  printf("%d\n", a);

  return 0;
}