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

#include "pc_stuff.h"

#define INPUT_STATUS (0x03da)
#define VBLANK (0x08)
#define BIOS_SET_VIDEO_MODE   (0x00)

byte *VGA = (byte *)0xA0000;

void setVideoMode(byte videoMode) {
  union REGS regs;

  regs.h.ah = BIOS_SET_VIDEO_MODE;
  regs.h.al = videoMode;
  int386(BIOS_VIDEO_INTERRUPT, &regs, &regs);
}

void waitStartVbl() {
    while (inp(INPUT_STATUS) & VBLANK);
}

void waitEndVbl() {
    while (!(inp(INPUT_STATUS) & VBLANK));
}

#define FAILSAFE (80)

void writeString(char *buffer, int x, int y) {
  union REGS regs;

  int i, currentX = x;
  char c;

  for (i = 0; i < FAILSAFE; ++i) {
    c = buffer[i];
    if (c == 0) break;

    regs.h.ah = 0x02;
    regs.h.bh = 0x00;
    regs.h.dh = y;
    regs.h.dl = currentX;
    int386(BIOS_VIDEO_INTERRUPT, &regs, &regs);

    regs.h.ah = 0x09;
    regs.h.al = c;
    regs.h.bh = 0x00;
    regs.h.bl = 1;
    regs.w.cx = 1;
    int386(BIOS_VIDEO_INTERRUPT, &regs, &regs);

    currentX++;
  }
}