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8bitworkshop/presets/zx/cosmic.c
2021-08-08 13:39:19 -04:00

611 lines
14 KiB
C

/*
* A ZX Spectrum port of the Cosmic Impalas game
* described in the book
* "Making 8-bit Arcade Games in C"
*/
#include <string.h>
#include "bios.h"
//#link "bios.c"
// type aliases for byte/signed byte/unsigned 16-bit
typedef unsigned char byte;
typedef signed char sbyte;
typedef unsigned short word;
// speaker click
__sfr __at (0xfe) portfe;
static byte spkr;
#define CLICK portfe = spkr ^= 0x10;
#define VHEIGHT 192 // number of scanlines
#define VBWIDTH 32 // number of bytes per scanline
#define PIXWIDTH 256 // 8 pixels per byte
// swap bits of address for ZX screen layout
// http://www.breakintoprogram.co.uk/computers/zx-spectrum/screen-memory-layout
// lookup table, starting address of each scanline (0 .. 191)
static byte* const vidmem[VHEIGHT] = {
0x4000, 0x4100, 0x4200, 0x4300
, 0x4400, 0x4500, 0x4600, 0x4700
, 0x4020, 0x4120, 0x4220, 0x4320
, 0x4420, 0x4520, 0x4620, 0x4720
, 0x4040, 0x4140, 0x4240, 0x4340
, 0x4440, 0x4540, 0x4640, 0x4740
, 0x4060, 0x4160, 0x4260, 0x4360
, 0x4460, 0x4560, 0x4660, 0x4760
, 0x4080, 0x4180, 0x4280, 0x4380
, 0x4480, 0x4580, 0x4680, 0x4780
, 0x40A0, 0x41A0, 0x42A0, 0x43A0
, 0x44A0, 0x45A0, 0x46A0, 0x47A0
, 0x40C0, 0x41C0, 0x42C0, 0x43C0
, 0x44C0, 0x45C0, 0x46C0, 0x47C0
, 0x40E0, 0x41E0, 0x42E0, 0x43E0
, 0x44E0, 0x45E0, 0x46E0, 0x47E0
, 0x4800, 0x4900, 0x4A00, 0x4B00
, 0x4C00, 0x4D00, 0x4E00, 0x4F00
, 0x4820, 0x4920, 0x4A20, 0x4B20
, 0x4C20, 0x4D20, 0x4E20, 0x4F20
, 0x4840, 0x4940, 0x4A40, 0x4B40
, 0x4C40, 0x4D40, 0x4E40, 0x4F40
, 0x4860, 0x4960, 0x4A60, 0x4B60
, 0x4C60, 0x4D60, 0x4E60, 0x4F60
, 0x4880, 0x4980, 0x4A80, 0x4B80
, 0x4C80, 0x4D80, 0x4E80, 0x4F80
, 0x48A0, 0x49A0, 0x4AA0, 0x4BA0
, 0x4CA0, 0x4DA0, 0x4EA0, 0x4FA0
, 0x48C0, 0x49C0, 0x4AC0, 0x4BC0
, 0x4CC0, 0x4DC0, 0x4EC0, 0x4FC0
, 0x48E0, 0x49E0, 0x4AE0, 0x4BE0
, 0x4CE0, 0x4DE0, 0x4EE0, 0x4FE0
, 0x5000, 0x5100, 0x5200, 0x5300
, 0x5400, 0x5500, 0x5600, 0x5700
, 0x5020, 0x5120, 0x5220, 0x5320
, 0x5420, 0x5520, 0x5620, 0x5720
, 0x5040, 0x5140, 0x5240, 0x5340
, 0x5440, 0x5540, 0x5640, 0x5740
, 0x5060, 0x5160, 0x5260, 0x5360
, 0x5460, 0x5560, 0x5660, 0x5760
, 0x5080, 0x5180, 0x5280, 0x5380
, 0x5480, 0x5580, 0x5680, 0x5780
, 0x50A0, 0x51A0, 0x52A0, 0x53A0
, 0x54A0, 0x55A0, 0x56A0, 0x57A0
, 0x50C0, 0x51C0, 0x52C0, 0x53C0
, 0x54C0, 0x55C0, 0x56C0, 0x57C0
, 0x50E0, 0x51E0, 0x52E0, 0x53E0
, 0x54E0, 0x55E0, 0x56E0, 0x57E0
};
// attribute table
byte __at(0x5800) vidattrs[24][32];
// bitmask table
const byte BIT8[8] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
/// 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
// draw (xor) vertical line
void xor_vline(byte x, byte y1, byte y2) {
byte xb = x>>3; // divide x by 8
byte mask = BIT8[x&7]; // 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
}
}
// clear screen and set graphics mode
void clrscr() {
memset(vidmem[0], 0, 0x1800); // clear page 1
memset(vidattrs, 0x4, 0x300); // set attributes
}
// 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 = x>>3; // xb = x DIV 8
byte xs = x&7; // xs = x MOD 8
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); break;
case OP_ERASE: *dest++ &= ~next; break;
}
rest = data << (8-xs); // save leftover bits
}
// compute final byte operation
switch (op) {
case OP_DRAW: *dest = rest; break;
case OP_XOR: result |= (*dest ^= 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 = x>>3;
for (j=0; j<h; j++) {
byte* dest = &vidmem[y++][xb];
for (i=0; i<=w; i++) {
dest[i] = 0;
}
}
}
// 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 16-bit BCD values
word bcd_add(word a, word b) __naked {
a; b; // to avoid warning
__asm
push ix
ld ix,#0
add ix,sp
ld a,4 (ix)
add a, 6 (ix)
daa
ld c,a
ld a,5 (ix)
adc a, 7 (ix)
daa
ld b,a
ld l, c
ld h, b
pop ix
ret
__endasm;
}
//
// GAME GRAPHICS
//
const byte player_bitmap[] =
{3,16,/*{w:24,h:16,bpp:1,brev:1}*/0x00,0x00,0x00,0x00,0x18,0x00,0x00,0x3C,0x00,0x04,0x18,0x20,0x04,0x18,0x20,0x0E,0x3C,0x70,0x1D,0x3C,0xB8,0x2C,0xE7,0x34,0x2E,0x66,0x74,0x25,0xE7,0xA4,0x34,0xDB,0x2C,0x2E,0x5A,0x74,0x2D,0xE7,0xB4,0x1C,0x3C,0x38,0x0D,0xDB,0xB0,0x07,0x18,0xE0};
const byte bomb_bitmap[] =
{1,5,/*{w:8,h:5,bpp:1,brev:1}*/0x88,0x55,0x77,0x55,0x88};
const byte bullet_bitmap[] =
{1,5,/*{w:8,h:5,bpp:1,brev:1}*/0x14,0x28,0x14,0x14,0x28};
const byte enemy1_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1,brev:1}*/0x00,0x00,0x7F,0xF8,0xF8,0x7C,0x8C,0xC4,0xAC,0xD4,0x8C,0xC4,0xFC,0xFC,0xF8,0x7C,0xF0,0x3C,0x8B,0x44,0xF3,0x3C,0xF3,0x3C,0xD3,0x2C,0x8C,0xC4,0x48,0x48,0x80,0x04};
const byte enemy2_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1,brev:1}*/0x00,0x00,0x30,0x0C,0x14,0x28,0x2F,0xF4,0x08,0x10,0x22,0x44,0xE0,0x07,0xD0,0x0B,0xB0,0x0D,0xB2,0x4D,0x19,0x98,0x8E,0x71,0x82,0x41,0xB1,0x8D,0x59,0x9A,0x4A,0x52};
const byte enemy3_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1,brev: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,0x64,0x26,0x20,0x04,0x00,0x00,0x00,0x00};
const byte enemy4_bitmap[] =
{2,16,/*{w:16,h:16,bpp:1,brev:1}*/0x00,0x00,0x00,0x00,0x37,0xEC,0x78,0x1E,0x5A,0x5A,0xFA,0x5F,0xF8,0x1F,0xF8,0x1F,0xF1,0x8F,0xA8,0x15,0xCC,0x33,0xE8,0x17,0x66,0x66,0x33,0xCC,0x0D,0xB0,0x00,0x00};
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;
a=0; b=0;
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-2; i++)
vidmem[191][i] = 0x55;
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, VHEIGHT-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) {
clear_sprite(e->shape, e->x, e->y);
memmove(e, e+1, sizeof(Enemy)*(enemies-e+MAX_ENEMIES-1));
num_enemies--; // update_next_enemy() will check enemy_index
tone(1,10,10);
}
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 >= 255-32) {
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+w && y >= e->y-h && y <= e->y+eh+h);
}
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, 4, 4)) {
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 + 13;
bullet_y = VHEIGHT-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 > VHEIGHT-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 > VHEIGHT-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 = keyscan();
// handle keyboard
if (key != 0xff) {
switch (key) {
case 0x04: // left arrow
player_dir = -2;
break;
case 0x13: // right arrow
player_dir = 2;
break;
case ' ': // space
if (bullet_y == 0) {
fire_bullet();
}
break;
}
} else {
player_dir = 0;
}
}
// move player
if (player_dir < 0 && player_x > 0)
player_x += player_dir;
else if (player_dir > 0 && player_x < 255-40)
player_x += player_dir;
draw_sprite(player_bitmap, player_x, VHEIGHT-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=8;
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() {
// NOTE: initializers don't get run, so we init here
while (1) {
//attract_mode();
play_game();
}
}