mirror of
https://github.com/sehugg/8bitworkshop.git
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611 lines
14 KiB
C
611 lines
14 KiB
C
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/*
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* A ZX Spectrum port of the Cosmic Impalas game
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* described in the book
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* "Making 8-bit Arcade Games in C"
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*/
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#include <string.h>
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#include "bios.h"
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//#link "bios.c"
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// type aliases for byte/signed byte/unsigned 16-bit
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typedef unsigned char byte;
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typedef signed char sbyte;
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typedef unsigned short word;
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// speaker click
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__sfr __at (0xfe) portfe;
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static byte spkr;
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#define CLICK portfe = spkr ^= 0x10;
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#define VHEIGHT 192 // number of scanlines
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#define VBWIDTH 32 // number of bytes per scanline
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#define PIXWIDTH 256 // 8 pixels per byte
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// swap bits of address for ZX screen layout
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// http://www.breakintoprogram.co.uk/computers/zx-spectrum/screen-memory-layout
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// lookup table, starting address of each scanline (0 .. 191)
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static byte* const vidmem[VHEIGHT] = {
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0x4000, 0x4100, 0x4200, 0x4300
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, 0x4400, 0x4500, 0x4600, 0x4700
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, 0x4020, 0x4120, 0x4220, 0x4320
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, 0x4420, 0x4520, 0x4620, 0x4720
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, 0x4040, 0x4140, 0x4240, 0x4340
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, 0x4440, 0x4540, 0x4640, 0x4740
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, 0x4060, 0x4160, 0x4260, 0x4360
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, 0x4460, 0x4560, 0x4660, 0x4760
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, 0x4080, 0x4180, 0x4280, 0x4380
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, 0x4480, 0x4580, 0x4680, 0x4780
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, 0x40A0, 0x41A0, 0x42A0, 0x43A0
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, 0x44A0, 0x45A0, 0x46A0, 0x47A0
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, 0x40C0, 0x41C0, 0x42C0, 0x43C0
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, 0x44C0, 0x45C0, 0x46C0, 0x47C0
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, 0x40E0, 0x41E0, 0x42E0, 0x43E0
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, 0x44E0, 0x45E0, 0x46E0, 0x47E0
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, 0x4800, 0x4900, 0x4A00, 0x4B00
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, 0x4C00, 0x4D00, 0x4E00, 0x4F00
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, 0x4820, 0x4920, 0x4A20, 0x4B20
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, 0x4C20, 0x4D20, 0x4E20, 0x4F20
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, 0x4840, 0x4940, 0x4A40, 0x4B40
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, 0x4C40, 0x4D40, 0x4E40, 0x4F40
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, 0x4860, 0x4960, 0x4A60, 0x4B60
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, 0x4C60, 0x4D60, 0x4E60, 0x4F60
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, 0x4880, 0x4980, 0x4A80, 0x4B80
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, 0x4C80, 0x4D80, 0x4E80, 0x4F80
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, 0x48A0, 0x49A0, 0x4AA0, 0x4BA0
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, 0x4CA0, 0x4DA0, 0x4EA0, 0x4FA0
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, 0x48C0, 0x49C0, 0x4AC0, 0x4BC0
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, 0x4CC0, 0x4DC0, 0x4EC0, 0x4FC0
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, 0x48E0, 0x49E0, 0x4AE0, 0x4BE0
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, 0x4CE0, 0x4DE0, 0x4EE0, 0x4FE0
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, 0x5000, 0x5100, 0x5200, 0x5300
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, 0x5400, 0x5500, 0x5600, 0x5700
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, 0x5020, 0x5120, 0x5220, 0x5320
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, 0x5420, 0x5520, 0x5620, 0x5720
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, 0x5040, 0x5140, 0x5240, 0x5340
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, 0x5440, 0x5540, 0x5640, 0x5740
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, 0x5060, 0x5160, 0x5260, 0x5360
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, 0x5460, 0x5560, 0x5660, 0x5760
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, 0x5080, 0x5180, 0x5280, 0x5380
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, 0x5480, 0x5580, 0x5680, 0x5780
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, 0x50A0, 0x51A0, 0x52A0, 0x53A0
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, 0x54A0, 0x55A0, 0x56A0, 0x57A0
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, 0x50C0, 0x51C0, 0x52C0, 0x53C0
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, 0x54C0, 0x55C0, 0x56C0, 0x57C0
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, 0x50E0, 0x51E0, 0x52E0, 0x53E0
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, 0x54E0, 0x55E0, 0x56E0, 0x57E0
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};
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// attribute table
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byte __at(0x5800) vidattrs[24][32];
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// bitmask table
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const byte BIT8[8] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
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/// SOUND FUNCTIONS
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void tone(byte period, byte dur, sbyte mod) {
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word i;
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while (dur--) {
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for (i=0; i<period; i++) ;
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CLICK;
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period += mod;
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}
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}
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/// GRAPHICS FUNCTIONS
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// draw (xor) vertical line
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void xor_vline(byte x, byte y1, byte y2) {
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byte xb = x>>3; // divide x by 8
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byte mask = BIT8[x&7]; // lookup bitmask for remainder
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byte y;
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for (y=y1; y<=y2; y++) {
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byte* dest = &vidmem[y][xb]; // lookup dest. address
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*dest ^= mask; // XOR mask with destination
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}
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}
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// clear screen and set graphics mode
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void clrscr() {
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memset(vidmem[0], 0, 0x1800); // clear page 1
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memset(vidattrs, 0x4, 0x300); // set attributes
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}
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// draw (xor) a pixel
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void xor_pixel(byte x, byte y) {
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xor_vline(x, y, y); // draw line with 1-pixel height
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}
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typedef enum {
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OP_DRAW, OP_XOR, OP_ERASE
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} GraphicsOperation;
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// render a sprite with the given graphics operation
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byte render_sprite(const byte* src, byte x, byte y, byte op) {
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byte i,j;
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byte w = *src++; // get width from 1st byte of sprite
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byte h = *src++; // get height from 2nd byte of sprite
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byte xb = x>>3; // xb = x DIV 8
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byte xs = x&7; // xs = x MOD 8
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byte result = 0; // result (used only with XOR)
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for (j=0; j<h; j++) {
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byte* dest = &vidmem[y++][xb]; // lookup video address
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byte rest = 0; // rest = leftover bits
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for (i=0; i<w; i++) {
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byte data = *src++; // get next sprite byte
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byte next = (data >> xs) | rest; // shift and OR with leftover
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// compute graphics operation, write to dest
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switch (op) {
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case OP_DRAW: *dest++ = next; break;
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case OP_XOR: result |= (*dest++ ^= next); break;
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case OP_ERASE: *dest++ &= ~next; break;
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}
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rest = data << (7-xs); // save leftover bits
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}
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// compute final byte operation
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switch (op) {
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case OP_DRAW: *dest = rest; break;
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case OP_XOR: result |= (*dest ^= rest); break;
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case OP_ERASE: *dest &= ~rest; break;
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}
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}
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return result;
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}
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void draw_sprite(const byte* src, byte x, byte y) {
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render_sprite(src, x, y, OP_DRAW);
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}
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// XOR returns non-zero if any pixels were overlapped
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byte xor_sprite(const byte* src, byte x, byte y) {
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return render_sprite(src, x, y, OP_XOR);
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}
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void erase_sprite(const byte* src, byte x, byte y) {
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render_sprite(src, x, y, OP_ERASE);
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}
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// clear just sets all bytes to 0, and is fast
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void clear_sprite(const byte* src, byte x, byte y) {
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byte i,j;
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byte w = *src++;
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byte h = *src++;
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byte xb = x>>3;
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for (j=0; j<h; j++) {
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byte* dest = &vidmem[y++][xb];
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for (i=0; i<=w; i++) {
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dest[i] = 0;
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}
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}
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}
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// draw character from column 0..39, row 0..23
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void draw_char(char ch, byte col, byte row) {
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byte i;
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const byte* src = &font8x8[(ch-LOCHAR)][0];
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byte y = row*8;
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for (i=0; i<8; i++) {
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byte* dest = &vidmem[y++][col];
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*dest = *src;
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src += 1;
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}
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}
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// draw string starting at row/col (vert 1 = draw vertical)
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void draw_string(const char* str, byte col, byte row, byte vert) {
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do {
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byte ch = *str++;
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if (!ch) break;
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draw_char(ch, col, row);
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if (vert) row++; else col++;
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} while (1);
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}
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// draw 4-digit BCD word
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void draw_bcd_word(word bcd, byte col, byte row, byte vert) {
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byte j;
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if (vert) row+=3; else col+=3; // move to rightmost digit
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for (j=0; j<4; j++) {
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draw_char('0'+(bcd&0xf), col, row);
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if (vert) row--; else col--;
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bcd >>= 4;
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}
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}
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// add two 16-bit BCD values
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word bcd_add(word a, word b) __naked {
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a; b; // to avoid warning
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__asm
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push ix
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ld ix,#0
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add ix,sp
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ld a,4 (ix)
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add a, 6 (ix)
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daa
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ld c,a
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ld a,5 (ix)
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adc a, 7 (ix)
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daa
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ld b,a
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ld l, c
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ld h, b
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pop ix
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ret
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__endasm;
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}
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//
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// GAME GRAPHICS
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//
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const byte player_bitmap[] =
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{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};
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const byte bomb_bitmap[] =
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{1,5,/*{w:8,h:5,bpp:1,brev:1}*/0x88,0x55,0x77,0x55,0x88};
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const byte bullet_bitmap[] =
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{1,5,/*{w:8,h:5,bpp:1,brev:1}*/0x14,0x28,0x14,0x14,0x28};
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const byte enemy1_bitmap[] =
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{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};
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const byte enemy2_bitmap[] =
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{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};
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const byte enemy3_bitmap[] =
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{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};
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const byte enemy4_bitmap[] =
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{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};
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const byte* const enemy_bitmaps[4] = {
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enemy1_bitmap,
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enemy2_bitmap,
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enemy3_bitmap,
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enemy4_bitmap
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};
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//
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// GAME CODE
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//
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byte attract;
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word score;
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byte lives;
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#define MAXLIVES 5
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byte player_x;
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byte bullet_x;
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byte bullet_y;
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byte bomb_x;
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byte bomb_y;
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typedef struct {
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byte x,y;
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const byte* shape; // need const here
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} Enemy;
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#define MAX_ENEMIES 28
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Enemy enemies[MAX_ENEMIES];
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byte enemy_index;
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byte num_enemies;
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typedef struct {
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int right:1;
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int down:1;
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} MarchMode;
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MarchMode this_mode, next_mode;
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void draw_lives() {
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byte i;
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byte n = lives;
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byte y = 18;
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byte x = VBWIDTH-1;
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for (i=0; i<MAXLIVES; i++) {
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draw_char(i<n?'*':' ', x, y++);
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}
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}
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void draw_score() {
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byte x = VBWIDTH-1;
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byte y = 10;
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draw_bcd_word(score, x, y, 1);
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}
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void draw_bunker(byte x, byte y, byte y2, byte h, byte w) {
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byte i,a,b;
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a=0; b=0;
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for (i=0; i<h; i++) {
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a = y-y2-i*2;
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b = y-i;
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xor_vline(x+i, a, b);
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xor_vline(x+h*2+w-i-1, a, b);
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}
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for (i=0; i<w; i++) {
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xor_vline(x+h+i, a, b);
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}
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}
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void draw_playfield() {
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byte i;
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clrscr();
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draw_string("PLAYER 1", VBWIDTH-1, 0, 1);
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draw_score();
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draw_lives();
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for (i=0; i<VBWIDTH-2; i++)
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vidmem[191][i] = 0x55;
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draw_bunker(20, 165, 15, 15, 20);
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draw_bunker(160, 165, 15, 15, 20);
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}
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void add_score(word pts) {
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if (attract) return;
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score = bcd_add(score, pts);
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draw_score();
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}
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void xor_player_derez() {
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byte i,j;
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byte x = player_x+13;
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byte y = 190;
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byte* rand = (byte*) &clrscr; // use code as random #'s
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for (j=1; j<=0x1f; j++) {
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for (i=0; i<50; i++) {
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signed char xx = x + (*rand++ & 0x1f) - 15;
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signed char yy = y - (*rand++ & j);
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xor_pixel(xx, yy);
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if ((xx & 0x1f) > j) { CLICK; }
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}
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}
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}
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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();
|
||
|
}
|
||
|
}
|