// reserve space for the HGR1 screen buffer
#define CFGFILE apple2-hgr.cfg
#pragma data-name(push,"HGR")
#pragma data-name(pop)

/*
 * An Apple ][ port of the Cosmic Impalas game 
 * described in the book
 * "Making 8-bit Arcade Games in C"
 */

#include <string.h>
#include <conio.h>
#include <apple2.h>
#include <peekpoke.h>

// type aliases for byte/signed byte/unsigned 16-bit
typedef unsigned char byte;
typedef signed char sbyte;
typedef unsigned short word;

// peeks, pokes, and strobes
#define STROBE(addr)       __asm__ ("sta %w", addr)

// speaker click
#define CLICK		   STROBE(0xc030)

/// HIRES LOOKUP TABLE

#define VHEIGHT 192	// number of scanlines
#define VBWIDTH 40	// number of bytes per scanline
#define PIXWIDTH 280	// 7 pixels per byte

#define LUT(x) (byte*)(0x2000|x)

// starting address of each scanline
static byte* const vidmem[VHEIGHT] = {
  LUT(0x0000), LUT(0x0400), LUT(0x0800), LUT(0x0c00), LUT(0x1000), LUT(0x1400), LUT(0x1800), LUT(0x1c00),
  LUT(0x0080), LUT(0x0480), LUT(0x0880), LUT(0x0c80), LUT(0x1080), LUT(0x1480), LUT(0x1880), LUT(0x1c80),
  LUT(0x0100), LUT(0x0500), LUT(0x0900), LUT(0x0d00), LUT(0x1100), LUT(0x1500), LUT(0x1900), LUT(0x1d00),
  LUT(0x0180), LUT(0x0580), LUT(0x0980), LUT(0x0d80), LUT(0x1180), LUT(0x1580), LUT(0x1980), LUT(0x1d80),
  LUT(0x0200), LUT(0x0600), LUT(0x0a00), LUT(0x0e00), LUT(0x1200), LUT(0x1600), LUT(0x1a00), LUT(0x1e00),
  LUT(0x0280), LUT(0x0680), LUT(0x0a80), LUT(0x0e80), LUT(0x1280), LUT(0x1680), LUT(0x1a80), LUT(0x1e80),
  LUT(0x0300), LUT(0x0700), LUT(0x0b00), LUT(0x0f00), LUT(0x1300), LUT(0x1700), LUT(0x1b00), LUT(0x1f00),
  LUT(0x0380), LUT(0x0780), LUT(0x0b80), LUT(0x0f80), LUT(0x1380), LUT(0x1780), LUT(0x1b80), LUT(0x1f80),
  LUT(0x0028), LUT(0x0428), LUT(0x0828), LUT(0x0c28), LUT(0x1028), LUT(0x1428), LUT(0x1828), LUT(0x1c28),
  LUT(0x00a8), LUT(0x04a8), LUT(0x08a8), LUT(0x0ca8), LUT(0x10a8), LUT(0x14a8), LUT(0x18a8), LUT(0x1ca8),
  LUT(0x0128), LUT(0x0528), LUT(0x0928), LUT(0x0d28), LUT(0x1128), LUT(0x1528), LUT(0x1928), LUT(0x1d28),
  LUT(0x01a8), LUT(0x05a8), LUT(0x09a8), LUT(0x0da8), LUT(0x11a8), LUT(0x15a8), LUT(0x19a8), LUT(0x1da8),
  LUT(0x0228), LUT(0x0628), LUT(0x0a28), LUT(0x0e28), LUT(0x1228), LUT(0x1628), LUT(0x1a28), LUT(0x1e28),
  LUT(0x02a8), LUT(0x06a8), LUT(0x0aa8), LUT(0x0ea8), LUT(0x12a8), LUT(0x16a8), LUT(0x1aa8), LUT(0x1ea8),
  LUT(0x0328), LUT(0x0728), LUT(0x0b28), LUT(0x0f28), LUT(0x1328), LUT(0x1728), LUT(0x1b28), LUT(0x1f28),
  LUT(0x03a8), LUT(0x07a8), LUT(0x0ba8), LUT(0x0fa8), LUT(0x13a8), LUT(0x17a8), LUT(0x1ba8), LUT(0x1fa8),
  LUT(0x0050), LUT(0x0450), LUT(0x0850), LUT(0x0c50), LUT(0x1050), LUT(0x1450), LUT(0x1850), LUT(0x1c50),
  LUT(0x00d0), LUT(0x04d0), LUT(0x08d0), LUT(0x0cd0), LUT(0x10d0), LUT(0x14d0), LUT(0x18d0), LUT(0x1cd0),
  LUT(0x0150), LUT(0x0550), LUT(0x0950), LUT(0x0d50), LUT(0x1150), LUT(0x1550), LUT(0x1950), LUT(0x1d50),
  LUT(0x01d0), LUT(0x05d0), LUT(0x09d0), LUT(0x0dd0), LUT(0x11d0), LUT(0x15d0), LUT(0x19d0), LUT(0x1dd0),
  LUT(0x0250), LUT(0x0650), LUT(0x0a50), LUT(0x0e50), LUT(0x1250), LUT(0x1650), LUT(0x1a50), LUT(0x1e50),
  LUT(0x02d0), LUT(0x06d0), LUT(0x0ad0), LUT(0x0ed0), LUT(0x12d0), LUT(0x16d0), LUT(0x1ad0), LUT(0x1ed0),
  LUT(0x0350), LUT(0x0750), LUT(0x0b50), LUT(0x0f50), LUT(0x1350), LUT(0x1750), LUT(0x1b50), LUT(0x1f50),
  LUT(0x03d0), LUT(0x07d0), LUT(0x0bd0), LUT(0x0fd0), LUT(0x13d0), LUT(0x17d0), LUT(0x1bd0), LUT(0x1fd0)
};

// divide-by 7 table
const byte DIV7[256] = {
 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4,
 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 9,
 9, 9, 9, 9, 9, 9,10,10,10,10,10,10,10,11,11,11,11,11,11,11,12,12,12,12,12,12,12,13,13,13,13,13,
13,13,14,14,14,14,14,14,14,15,15,15,15,15,15,15,16,16,16,16,16,16,16,17,17,17,17,17,17,17,18,18,
18,18,18,18,18,19,19,19,19,19,19,19,20,20,20,20,20,20,20,21,21,21,21,21,21,21,22,22,22,22,22,22,
22,23,23,23,23,23,23,23,24,24,24,24,24,24,24,25,25,25,25,25,25,25,26,26,26,26,26,26,26,27,27,27,
27,27,27,27,28,28,28,28,28,28,28,29,29,29,29,29,29,29,30,30,30,30,30,30,30,31,31,31,31,31,31,31,
32,32,32,32,32,32,32,33,33,33,33,33,33,33,34,34,34,34,34,34,34,35,35,35,35,35,35,35,36,36,36,36};

// modulo-by-7 table
const byte MOD7[256] = {
 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3,
 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0,
 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4,
 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1,
 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5,
 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2,
 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6,
 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3, 4, 5, 6, 0, 1, 2, 3};

// bitmask table
const byte BIT7[7] = { 1, 2, 4, 8, 16, 32, 64 };

/// SOUND FUNCTIONS

void tone(byte period, byte dur, sbyte mod) {
  word i;
  while (dur--) {
    for (i=0; i<period; i++) ;
    CLICK;
    period += mod;
  }
}

/// GRAPHICS FUNCTIONS

// clear screen and set graphics mode
void clrscr() {
  STROBE(0xc052); // turn off mixed-mode
  STROBE(0xc054); // page 1
  STROBE(0xc057); // hi-res
  STROBE(0xc050); // set graphics mode
  memset((byte*)0x2000, 0, 0x2000); // clear page 1
}

// draw (xor) vertical line
void xor_vline(byte x, byte y1, byte y2) {
  byte xb = DIV7[x];		// divide x by 7
  byte mask = BIT7[MOD7[x]];	// lookup bitmask for remainder
  byte y;
  for (y=y1; y<=y2; y++) {
    byte* dest = &vidmem[y][xb]; // lookup dest. address
    *dest ^= mask;		 // XOR mask with destination
  }
}

// draw (xor) a pixel
void xor_pixel(byte x, byte y) {
  xor_vline(x, y, y);		// draw line with 1-pixel height
}

typedef enum {
  OP_DRAW, OP_XOR, OP_ERASE
} GraphicsOperation;

// render a sprite with the given graphics operation
byte render_sprite(const byte* src, byte x, byte y, byte op) {
  byte i,j;
  byte w = *src++;	// get width from 1st byte of sprite
  byte h = *src++;	// get height from 2nd byte of sprite
  byte xb = DIV7[x];	// xb = x DIV 7
  byte xs = MOD7[x];	// xs = x MOD 7
  byte result = 0;	// result (used only with XOR)
  for (j=0; j<h; j++) {
    byte* dest = &vidmem[y++][xb];	// lookup video address
    byte rest = 0;			// rest = leftover bits
    for (i=0; i<w; i++) {
      byte data = *src++;		// get next sprite byte
      byte next = (data << xs) | rest; // shift and OR with leftover
      // compute graphics operation, write to dest
      switch (op) {
        case OP_DRAW:  *dest++ = next; break;
        case OP_XOR:   result |= (*dest++ ^= next) & next; break;
        case OP_ERASE: *dest++ &= ~next; break;
      }
      rest = data >> (7-xs);	// save leftover bits
    }
    // compute final byte operation
    switch (op) {
      case OP_DRAW:  *dest = rest; break;
      case OP_XOR:   result |= (*dest ^= rest) & rest; break;
      case OP_ERASE: *dest &= ~rest; break;
    }
  }
  return result;
}

void draw_sprite(const byte* src, byte x, byte y) {
  render_sprite(src, x, y, OP_DRAW);
}

// XOR returns non-zero if any pixels were overlapped
byte xor_sprite(const byte* src, byte x, byte y) {
  return render_sprite(src, x, y, OP_XOR);
}

void erase_sprite(const byte* src, byte x, byte y) {
  render_sprite(src, x, y, OP_ERASE);
}

// clear just sets all bytes to 0, and is fast
void clear_sprite(const byte* src, byte x, byte y) {
  byte i,j;
  byte w = *src++;
  byte h = *src++;
  byte xb = DIV7[x];
  for (j=0; j<h; j++) {
    byte* dest = &vidmem[y++][xb];
    for (i=0; i<=w; i++) {
      dest[i] = 0;
    }
  }
}

// FONT FUNCTIONS

#define LOCHAR 0x20	// lowest character value in font
#define HICHAR 0x7f	// highest character value in font

const byte font8x8[HICHAR-LOCHAR+1][8] = {/*{w:8,h:8,bpp:1,count:96}*/
{ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 }, { 0x18,0x18,0x18,0x18,0x00,0x00,0x18,0x00 }, { 0x66,0x66,0x66,0x00,0x00,0x00,0x00,0x00 }, { 0x66,0x66,0xff,0x66,0xff,0x66,0x66,0x00 }, { 0x18,0x7c,0x06,0x3c,0x60,0x3e,0x18,0x00 }, { 0x46,0x66,0x30,0x18,0x0c,0x66,0x62,0x00 }, { 0x3c,0x66,0x3c,0x1c,0xe6,0x66,0xfc,0x00 }, { 0x60,0x30,0x18,0x00,0x00,0x00,0x00,0x00 }, { 0x30,0x18,0x0c,0x0c,0x0c,0x18,0x30,0x00 }, { 0x0c,0x18,0x30,0x30,0x30,0x18,0x0c,0x00 }, { 0x00,0x66,0x3c,0xff,0x3c,0x66,0x00,0x00 }, { 0x00,0x18,0x18,0x7e,0x18,0x18,0x00,0x00 }, { 0x00,0x00,0x00,0x00,0x00,0x18,0x18,0x0c }, { 0x00,0x00,0x00,0x7e,0x00,0x00,0x00,0x00 }, { 0x00,0x00,0x00,0x00,0x00,0x18,0x18,0x00 }, { 0x00,0xc0,0x60,0x30,0x18,0x0c,0x06,0x00 }, { 0x3c,0x66,0x76,0x6e,0x66,0x66,0x3c,0x00 }, { 0x18,0x18,0x1c,0x18,0x18,0x18,0x7e,0x00 }, { 0x3c,0x66,0x60,0x30,0x0c,0x06,0x7e,0x00 }, { 0x3c,0x66,0x60,0x38,0x60,0x66,0x3c,0x00 }, { 0x60,0x70,0x78,0x66,0xfe,0x60,0x60,0x00 }, { 0x7e,0x06,0x3e,0x60,0x60,0x66,0x3c,0x00 }, { 0x3c,0x66,0x06,0x3e,0x66,0x66,0x3c,0x00 }, { 0x7e,0x66,0x30,0x18,0x18,0x18,0x18,0x00 }, { 0x3c,0x66,0x66,0x3c,0x66,0x66,0x3c,0x00 }, { 0x3c,0x66,0x66,0x7c,0x60,0x66,0x3c,0x00 }, { 0x00,0x00,0x18,0x00,0x00,0x18,0x00,0x00 }, { 0x00,0x00,0x18,0x00,0x00,0x18,0x18,0x0c }, { 0x70,0x18,0x0c,0x06,0x0c,0x18,0x70,0x00 }, { 0x00,0x00,0x7e,0x00,0x7e,0x00,0x00,0x00 }, { 0x0e,0x18,0x30,0x60,0x30,0x18,0x0e,0x00 }, { 0x3c,0x66,0x60,0x30,0x18,0x00,0x18,0x00 }, { 0x3c,0x66,0x76,0x76,0x06,0x46,0x3c,0x00 }, { 0x18,0x3c,0x66,0x7e,0x66,0x66,0x66,0x00 }, { 0x3e,0x66,0x66,0x3e,0x66,0x66,0x3e,0x00 }, { 0x3c,0x66,0x06,0x06,0x06,0x66,0x3c,0x00 }, { 0x1e,0x36,0x66,0x66,0x66,0x36,0x1e,0x00 }, { 0x7e,0x06,0x06,0x1e,0x06,0x06,0x7e,0x00 }, { 0x7e,0x06,0x06,0x1e,0x06,0x06,0x06,0x00 }, { 0x3c,0x66,0x06,0x76,0x66,0x66,0x3c,0x00 }, { 0x66,0x66,0x66,0x7e,0x66,0x66,0x66,0x00 }, { 0x3c,0x18,0x18,0x18,0x18,0x18,0x3c,0x00 }, { 0x78,0x30,0x30,0x30,0x30,0x36,0x1c,0x00 }, { 0x66,0x36,0x1e,0x0e,0x1e,0x36,0x66,0x00 }, { 0x06,0x06,0x06,0x06,0x06,0x06,0x7e,0x00 }, { 0xc6,0xee,0xfe,0xd6,0xc6,0xc6,0xc6,0x00 }, { 0x66,0x6e,0x7e,0x7e,0x76,0x66,0x66,0x00 }, { 0x3c,0x66,0x66,0x66,0x66,0x66,0x3c,0x00 }, { 0x3e,0x66,0x66,0x3e,0x06,0x06,0x06,0x00 }, { 0x3c,0x66,0x66,0x66,0x66,0x3c,0x70,0x00 }, { 0x3e,0x66,0x66,0x3e,0x1e,0x36,0x66,0x00 }, { 0x3c,0x66,0x06,0x3c,0x60,0x66,0x3c,0x00 }, { 0x7e,0x18,0x18,0x18,0x18,0x18,0x18,0x00 }, { 0x66,0x66,0x66,0x66,0x66,0x66,0x3c,0x00 }, { 0x66,0x66,0x66,0x66,0x66,0x3c,0x18,0x00 }, { 0xc6,0xc6,0xc6,0xd6,0xfe,0xee,0xc6,0x00 }, { 0x66,0x66,0x3c,0x18,0x3c,0x66,0x66,0x00 }, { 0x66,0x66,0x66,0x3c,0x18,0x18,0x18,0x00 }, { 0x7e,0x60,0x30,0x18,0x0c,0x06,0x7e,0x00 }, { 0x3c,0x0c,0x0c,0x0c,0x0c,0x0c,0x3c,0x00 }, { 0x00,0x06,0x0c,0x18,0x30,0x60,0xc0,0x00 }, { 0x3c,0x30,0x30,0x30,0x30,0x30,0x3c,0x00 }, { 0x00,0x18,0x3c,0x7e,0x18,0x18,0x18,0x18 }, { 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0xff }, { 0x06,0x0c,0x18,0x00,0x00,0x00,0x00,0x00 }, { 0x00,0x00,0x3c,0x60,0x7c,0x66,0x7c,0x00 }, { 0x00,0x06,0x06,0x3e,0x66,0x66,0x3e,0x00 }, { 0x00,0x00,0x3c,0x06,0x06,0x06,0x3c,0x00 }, { 0x00,0x60,0x60,0x7c,0x66,0x66,0x7c,0x00 }, { 0x00,0x00,0x3c,0x66,0x7e,0x06,0x3c,0x00 }, { 0x00,0x70,0x18,0x7c,0x18,0x18,0x18,0x00 }, { 0x00,0x00,0x7c,0x66,0x66,0x7c,0x60,0x3e }, { 0x00,0x06,0x06,0x3e,0x66,0x66,0x66,0x00 }, { 0x00,0x18,0x00,0x1c,0x18,0x18,0x3c,0x00 }, { 0x00,0x60,0x00,0x60,0x60,0x60,0x60,0x3c }, { 0x00,0x06,0x06,0x36,0x1e,0x36,0x66,0x00 }, { 0x00,0x1c,0x18,0x18,0x18,0x18,0x3c,0x00 }, { 0x00,0x00,0x66,0xfe,0xfe,0xd6,0xc6,0x00 }, { 0x00,0x00,0x3e,0x66,0x66,0x66,0x66,0x00 }, { 0x00,0x00,0x3c,0x66,0x66,0x66,0x3c,0x00 }, { 0x00,0x00,0x3e,0x66,0x66,0x3e,0x06,0x06 }, { 0x00,0x00,0x7c,0x66,0x66,0x7c,0x60,0x60 }, { 0x00,0x00,0x3e,0x66,0x06,0x06,0x06,0x00 }, { 0x00,0x00,0x7c,0x06,0x3c,0x60,0x3e,0x00 }, { 0x00,0x18,0x7e,0x18,0x18,0x18,0x70,0x00 }, { 0x00,0x00,0x66,0x66,0x66,0x66,0x7c,0x00 }, { 0x00,0x00,0x66,0x66,0x66,0x3c,0x18,0x00 }, { 0x00,0x00,0xc6,0xd6,0xfe,0x7c,0x6c,0x00 }, { 0x00,0x00,0x66,0x3c,0x18,0x3c,0x66,0x00 }, { 0x00,0x00,0x66,0x66,0x66,0x7c,0x30,0x1e }, { 0x00,0x00,0x7e,0x30,0x18,0x0c,0x7e,0x00 }, { 0x38,0x0c,0x0c,0x06,0x0c,0x0c,0x38,0x00 }, { 0x18,0x18,0x18,0x18,0x18,0x18,0x18,0x18 }, { 0x1c,0x30,0x30,0x60,0x30,0x30,0x1c,0x00 }, { 0x00,0x4c,0x32,0x00,0x00,0x00,0x00,0x00 }, { 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 },
};

// draw character from column 0..39, row 0..23
void draw_char(char ch, byte col, byte row) {
  byte i;
  const byte* src = &font8x8[(ch-LOCHAR)][0];
  byte y = row*8;
  for (i=0; i<8; i++) {
    byte* dest = &vidmem[y++][col];
    *dest = *src;
    src += 1;
  }
}

// draw string starting at row/col (vert 1 = draw vertical)
void draw_string(const char* str, byte col, byte row, byte vert) {
  do {
    byte ch = *str++;
    if (!ch) break;
    draw_char(ch, col, row);
    if (vert) row++; else col++;
  } while (1);
}

// draw 4-digit BCD word
void draw_bcd_word(word bcd, byte col, byte row, byte vert) {
  byte j;
  if (vert) row+=3; else col+=3; // move to rightmost digit
  for (j=0; j<4; j++) {
    draw_char('0'+(bcd&0xf), col, row);
    if (vert) row--; else col--;
    bcd >>= 4;
  }
}

// add two 4-digit BCD words
word bcd_add(word a, word b) {
  word result;
  __asm__ ("sed"); // set decimal (BCD) mode
  result = a+b;
  __asm__ ("cld"); // clear BCD mode
  return result;
}

//
// GAME GRAPHICS
//

const byte player_bitmap[] =
{3,16,/*{w:24,h:16,bpp:1}*/0x00,0x00,0x00,0x00,0x18,0x00,0x00,0x3C,0x00,0x04,0x18,0x20,0x04,0x18,0x20,0x0C,0x3C,0x30,0x3C,0x3C,0x3C,0xCC,0xE7,0x33,0x0C,0x66,0x30,0xC4,0xE7,0x23,0x34,0xE7,0x2C,0x0C,0x7E,0x30,0xCC,0xFF,0x33,0x3C,0x18,0x3C,0x0C,0x18,0x30,0x04,0x18,0x20};
const byte bomb_bitmap[] =
{1,5,/*{w:8,h:5,bpp:1}*/0x88,0x55,0x77,0x55,0x88};
const byte bullet_bitmap[] =
{1,5,/*{w:8,h:5,bpp:1}*/0x14,0x28,0x14,0x14,0x28};
const byte enemy1_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1}*/0x00,0x00,0x70,0x38,0xF8,0x7C,0xFC,0xFC,0xFE,0xFC,0xFE,0xFF,0xFC,0xFF,0xF8,0x7F,0xF0,0x3F,0x88,0x47,0xF0,0x3F,0xF0,0x3F,0xD0,0x2F,0x8C,0xC7,0x48,0x48,0x80,0x04};
const byte enemy2_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1}*/0x00,0x00,0x30,0x0C,0x10,0x08,0x3C,0x3D,0x2C,0x35,0x34,0x2D,0x24,0x25,0x50,0x15,0x28,0x0A,0x30,0x0D,0x28,0x15,0x4A,0x50,0x2A,0x55,0x22,0x05,0x0A,0x14,0x0A,0x50};
const byte enemy3_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1}*/0x00,0x00,0x00,0x00,0x04,0x20,0x05,0xA0,0x05,0xA0,0x25,0xA4,0xA7,0xE5,0xF7,0xEF,0xF7,0xEF,0xFE,0x7F,0xFC,0x3F,0xBC,0x3D,0xE4,0x27,0x20,0x00,0x00,0x00,0x00,0x00};
const byte enemy4_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1}*/0x00,0x00,0x00,0x00,0xF0,0x0F,0xF8,0x1F,0xD8,0x1B,0xF8,0x1F,0xF8,0x1F,0xF8,0x1F,0xF0,0x0F,0xA8,0x15,0xCC,0x33,0xE8,0x17,0x66,0x66,0x33,0xCC,0x61,0x86,0x40,0x02};
const byte explosion_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1}*/0x40,0x00,0x02,0x44,0x08,0x20,0x40,0x02,0x28,0x14,0x54,0x2A,0x2A,0x54,0x55,0xAA,0x2A,0x54,0x55,0xAA,0x2A,0x54,0x54,0x2A,0x28,0x14,0x40,0x22,0x04,0x40,0x42,0x04};

const byte* const enemy_bitmaps[4] = {
  enemy1_bitmap,
  enemy2_bitmap,
  enemy3_bitmap,
  enemy4_bitmap
};

//
// GAME CODE
//

byte attract;
word score;
byte lives;

#define MAXLIVES 5

byte player_x;
byte bullet_x;
byte bullet_y;
byte bomb_x;
byte bomb_y;

typedef struct {
  byte x,y;
  const byte* shape; // need const here
} Enemy;

#define MAX_ENEMIES 28

Enemy enemies[MAX_ENEMIES];
byte enemy_index;
byte num_enemies;

typedef struct {
  int right:1;
  int down:1;
} MarchMode;

MarchMode this_mode, next_mode;

void draw_lives() {
  byte i;
  byte n = lives;
  byte y = 18;
  byte x = VBWIDTH-1;
  for (i=0; i<MAXLIVES; i++) {
    draw_char(i<n?'*':' ', x, y++);
  }
}

void draw_score() {
  byte x = VBWIDTH-1;
  byte y = 10;
  draw_bcd_word(score, x, y, 1);
}

void draw_bunker(byte x, byte y, byte y2, byte h, byte w) {
  byte i,a,b;
  for (i=0; i<h; i++) {
    a = y-y2-i*2;
    b = y-i;
    xor_vline(x+i, a, b);
    xor_vline(x+h*2+w-i-1, a, b);
  }
  for (i=0; i<w; i++) {
    xor_vline(x+h+i, a, b);
  }
}

void draw_playfield() {
  byte i;
  clrscr();
  draw_string("PLAYER 1", VBWIDTH-1, 0, 1);
  draw_score();
  draw_lives();
  for (i=0; i<VBWIDTH-4; i++)
    vidmem[191][i] = (i&1) ? 0x55 : 0x2a;
  draw_bunker(20, 165, 15, 15, 20);
  draw_bunker(160, 165, 15, 15, 20);
}

void add_score(word pts) {
  if (attract) return;
  score = bcd_add(score, pts);
  draw_score();
}

void xor_player_derez() {
  byte i,j;
  byte x = player_x+13;
  byte y = 190;
  byte* rand = (byte*) &clrscr; // use code as random #'s
  for (j=1; j<=0x1f; j++) {
    for (i=0; i<50; i++) {
      signed char xx = x + (*rand++ & 0x1f) - 15;
      signed char yy = y - (*rand++ & j);
      xor_pixel(xx, yy);
      if ((xx & 0x1f) > j) { CLICK; }
    }
  }
}

void destroy_player() {
  xor_player_derez(); // xor derez pattern
  xor_sprite(player_bitmap, player_x, 192-17); // erase ship via xor
  xor_player_derez(); // xor 2x to erase derez pattern
  player_x = 0xff;
  lives--;
}

void init_enemies() {
  byte i,x,y,bm;
  x=0;
  y=10;
  bm=0;
  for (i=0; i<MAX_ENEMIES; i++) {
    Enemy* e = &enemies[i];
    e->x = x;
    e->y = y;
    e->shape = enemy_bitmaps[bm];
    x += 29;
    if (x >= 200) {
      x = 0;
      y += 20;
      bm++;
    }
  }
  enemy_index = 0;
  num_enemies = MAX_ENEMIES;
  this_mode.right = 1;
  this_mode.down = 0;
  next_mode.right = 1;
  next_mode.down = 0;
}

void delete_enemy(Enemy* e) {
  byte x = e->x;
  byte y = e->y;
  clear_sprite(e->shape, x, y);
  xor_sprite(explosion_bitmap, x, y);
  memmove(e, e+1, sizeof(Enemy)*(enemies-e+MAX_ENEMIES-1));
  num_enemies--; // update_next_enemy() will check enemy_index
  tone(1,20,10);
  xor_sprite(explosion_bitmap, x, y);
}

void update_next_enemy() {
  Enemy* e;
  if (enemy_index >= num_enemies) {
    enemy_index = 0;
    memcpy(&this_mode, &next_mode, sizeof(this_mode));
    tone(220+num_enemies,3,1);
  }
  e = &enemies[enemy_index];
  clear_sprite(e->shape, e->x, e->y);
  if (this_mode.down) {
    e->y += 4;
    // if too close to ground, end game
    if (e->y > 170) {
      destroy_player();
      lives = 0;
    }
    next_mode.down = 0;
  } else {
    if (this_mode.right) {
      e->x += 2;
      if (e->x >= 255-16) {
        next_mode.down = 1;
        next_mode.right = 0;
      }
    } else {
      e->x -= 2;
      if (e->x == 0) {
        next_mode.down = 1;
        next_mode.right = 1;
      }
    }
  }
  draw_sprite(e->shape, e->x, e->y);
  enemy_index++;
}

char in_rect(Enemy* e, byte x, byte y, byte w, byte h) {
  byte ew = e->shape[0]*8;
  byte eh = e->shape[1];
  return (x >= e->x-w && x <= e->x+ew && y >= e->y-h && y <= e->y+eh);
}

Enemy* find_enemy_at(byte x, byte y) {
  byte i;
  for (i=0; i<num_enemies; i++) {
    Enemy* e = &enemies[i];
    if (in_rect(e, x, y, 6, 2)) {
      return e;
    }
  }
  return NULL;
}

void check_bullet_hit(byte x, byte y) {
  Enemy* e = find_enemy_at(x,y);
  if (e) {
    delete_enemy(e);
    add_score(0x25);
  }
}

void fire_bullet() {
  bullet_x = player_x + 8;
  bullet_y = 192-22;
  xor_sprite(bullet_bitmap, bullet_x, bullet_y); // draw
}

void move_bullet() {
  byte leftover = xor_sprite(bullet_bitmap, bullet_x, bullet_y); // erase
  if (leftover || bullet_y < 10) {
    clear_sprite(bullet_bitmap, bullet_x, bullet_y);
    check_bullet_hit(bullet_x, bullet_y+2);
    bullet_y = 0;
  } else {
    bullet_y -= 4;
    tone(bullet_y,3,0);
    xor_sprite(bullet_bitmap, bullet_x, bullet_y); // draw
  }
}

void drop_bomb() {
  Enemy* e = &enemies[enemy_index];
  bomb_x = e->x + 7;
  bomb_y = e->y + 16;
  xor_sprite(bomb_bitmap, bomb_x, bomb_y);
}

void move_bomb() {
  byte leftover = xor_sprite(bomb_bitmap, bomb_x, bomb_y); // erase
  if (bomb_y > 192-12) {
    bomb_y = 0;
  } else if (leftover & 0x7f) { // don't count hi bit
    erase_sprite(bomb_bitmap, bomb_x, bomb_y); // erase bunker
    if (bomb_y > 192-23) {
      // player was hit (probably)
      destroy_player();
    }
    bomb_y = 0;
  } else {
    bomb_y += 3;
    xor_sprite(bomb_bitmap, bomb_x, bomb_y);
  }
}

byte frame;
signed char player_dir = 0;

void move_player() {
  if (attract) {
    if (bullet_y == 0) fire_bullet();
    player_dir = 0;
  } else {
    char key;
    // handle keyboard 
    if (kbhit()) {
      key = cgetc();
      switch (key) {
        case 8: // left arrow
          player_dir = player_dir < 0 ? 0 : -2;
          break;
        case 21: // right arrow
          player_dir = player_dir > 0 ? 0 : 2;
          break;
        case ' ': // space
          if (bullet_y == 0) {
            fire_bullet();
          }
          break;
      }
    }
  }
  // move player
  if (player_dir < 0 && player_x > 0)
    player_x += player_dir;
  else if (player_dir > 0 && player_x < 255-28)
    player_x += player_dir;
  draw_sprite(player_bitmap, player_x, 192-17);
}

void play_round() {
  draw_playfield();
  player_x = VHEIGHT/2-8;
  bullet_y = 0;
  bomb_y = 0;
  frame = 0;
  while (player_x != 0xff && num_enemies) {
    move_player();
    if (bullet_y) {
      move_bullet();
    }
    update_next_enemy();
    if (frame & 1) {
      if (bomb_y == 0) {
        drop_bomb();
      } else {
        move_bomb();
      }
    }
    frame++;
  }
}

void init_game() {
  score = 0;
  lives = 5;
}

void game_over_msg() {
  byte i;
  byte x=11;
  byte y=10;
  for (i=0; i<50; i++) {
    draw_string(" *************** ", x, y+0, 0);
    draw_string("***           ***", x, y+1, 0);
    draw_string("**  GAME OVER  **", x, y+2, 0);
    draw_string("***           ***", x, y+3, 0);
    draw_string(" *************** ", x, y+4, 0);
  }
}

void play_game() {
  attract = 0;
  init_game();
  init_enemies();
  while (lives) {
    play_round();
    if (num_enemies == 0) {
      init_enemies();
    }
  }
  game_over_msg();
}

void attract_mode() {
  attract = 1;
  while (1) {
    init_enemies();
    play_round();
  }
}

void main() {
  while (1) {
    play_game();
  }
}