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vaders.c
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vaders.c
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#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif
#include <SDL.h>
#include <stdio.h>
#include <stdlib.h>
#define W 224
#define H 256
#define PIXEL_SCALE 4
#define WINDOW_W (W*PIXEL_SCALE)
#define WINDOW_H (H*PIXEL_SCALE)
typedef uint8_t bool_t;
#define TRUE 1
#define FALSE 0
// https://segaretro.org/Palette
// 64 colors available on Master System
static const uint8_t LUMINOSITY[] = { 0, 85, 170, 255 };
static uint32_t FULL_PALETTE[64];
void init_palette() {
int i = 0;
for (int g = 0; g < 4; g++) {
for (int r = 0; r < 4; r++) {
for (int b = 0; b < 4; b++) {
FULL_PALETTE[i] =
0xff000000 |
LUMINOSITY[r] << 16 |
LUMINOSITY[g] << 8 |
LUMINOSITY[b] << 0;
i += 1;
}
}
}
}
static uint32_t pixels_argb[W*H];
#define SPRITE_DIM 8
const uint8_t SPRITE_DATA[][SPRITE_DIM] = {
{ // alien frame 1
0b00100100,
0b00011000,
0b00111100,
0b01011010,
0b11111111,
0b10111101,
0b10100101,
0b00100100
}, {// alien frame 2
0b00100100,
0b10011001,
0b10111101,
0b11011011,
0b01111110,
0b00111100,
0b01000010,
0b10000001
}, {// player
0b00011000,
0b00011000,
0b00111100,
0b00111100,
0b01111110,
0b01111110,
0b11111111,
0b11111111,
}, { // player shot
0b00011000,
0b00011000,
0b00011000,
0b00011000,
0b00011000,
0b00011000,
0b00011000,
0b00011000
}, { // enemy shot
0b00010000,
0b00001000,
0b00010000,
0b00001000,
0b00010000,
0b00001000,
0b00010000,
0b00001000,
}, { // explosion
0b01000010,
0b00100100,
0b10000001,
0b01000010,
0b01000010,
0b10000001,
0b00100100,
0b01000010
}
};
typedef struct {
uint8_t enable;
uint8_t x;
uint8_t y;
uint8_t idx;
uint8_t color;
} Sprite_t;
#define N_SPRITES 64
#define ENEMY_ROWS 5
#define ENEMY_COLS 11
#define N_ENEMIES (ENEMY_ROWS*ENEMY_COLS)
#define PLAYER_COLOR 18
static Sprite_t sprite[N_SPRITES];
#define SPRITE_PLAYER 63
#define SPRITE_PLAYER_SHOT 62
#define SPRITE_ENEMY_RETURN_SHOT 61
#define SPRITE_ENEMY_RANDOM_SHOT 60
#define SPRITE_LIVES N_ENEMIES
#define SHOT_SPEED 4
static uint8_t joyport;
#define LEFT 1
#define RIGHT 2
#define BUTTON_A 16
static int lives;
// frame counter
typedef unsigned int Tick_t;
static Tick_t ticks;
#define N_TIMERS 5
typedef struct {
Tick_t t;
void (*callback)();
} Timer_t;
static Timer_t timer[N_TIMERS];
#define TIMER_RETURN_SHOT 0
#define TIMER_CLEAR_EXPLOSIONS 1
#define TIMER_RESTORE_PLAYER 2
#define TIMER_MUSIC 3
#define TIMER_RANDOM_SHOT 4
static int enemies;
static int enemy_dir;
#define DIR_RIGHT 2
#define DIR_LEFT -2
void init_timers() {
for (int i = 0; i < N_TIMERS; i++) {
timer[i].t = 0;
}
}
void init_sprites() {
for (int i = 0; i < N_SPRITES; i++) {
sprite[i].enable = FALSE;
}
}
typedef enum {
NONE,
NOISE,
SQUARE
} Waveform_t;
typedef struct {
float f_start;
float f_decay;
float a_start;
float a_decay;
Waveform_t waveform;
int i;
float f_current;
float a_current;
} Sound_t;
Sound_t sound;
static void play_sound(Waveform_t waveform, float f_start, float f_decay, float a_start, float a_decay) {
sound.i = 0;
sound.waveform = waveform;
sound.f_start = f_start;
sound.f_decay = f_decay;
sound.a_start = a_start;
sound.a_decay = a_decay;
sound.f_current = sound.f_start;
sound.a_current = sound.a_start;
}
void init_player_sprite() {
Sprite_t* player = &sprite[SPRITE_PLAYER];
player->enable = 1;
player->x = W/2;
player->y = H-8;
player->color = PLAYER_COLOR;
player->idx = 2;
Sprite_t* life = &sprite[SPRITE_LIVES];
for (int i = 0; i < 3; i++) {
life->enable = i < lives;
life->x = i * SPRITE_DIM * 2;
life->y = 0;
life->color = PLAYER_COLOR;
life->idx = 2;
life++;
}
}
static void init_enemies() {
enemies = ENEMY_ROWS * ENEMY_COLS;
enemy_dir = DIR_RIGHT;
for (uint8_t j = 0; j < ENEMY_ROWS; j++) {
for (uint8_t i = 0; i < ENEMY_COLS; i++) {
Sprite_t* spr = &sprite[j*ENEMY_COLS+i];
spr->enable = 1;
spr->x = 16 + i*16;
spr->y = 64 + j*16;
spr->idx = 0;
spr->color = j*8+21;
}
}
}
// find the enemy nearest the player for returning fire
static int find_nearest_enemy_index() {
int nearest_i = -1;
int nearest_dx = 0xffff;
for (int i = 0; i < N_ENEMIES; i++) {
if (!sprite[i].enable) continue;
int dx = abs(sprite[i].x - sprite[SPRITE_PLAYER].x);
if (dx <= nearest_dx) {
nearest_dx = dx;
nearest_i = i;
}
}
return nearest_i;
}
// find a random enemy
static int find_random_enemy_index() {
int i = rand() % enemies;
int k = 0;
for (int j = 0; j < N_ENEMIES; j++) {
if (sprite[j].enable) {
k++;
}
if (k == i) {
return j;
}
}
return -1;
}
static void return_shot() {
Sprite_t *spr = &sprite[SPRITE_ENEMY_RETURN_SHOT];
spr->enable = TRUE;
int i = find_nearest_enemy_index();
spr->x = sprite[i].x;
spr->y = sprite[i].y + SPRITE_DIM;
spr->color = sprite[i].color;
spr->idx = 4;
}
static void random_shot() {
Sprite_t *spr = &sprite[SPRITE_ENEMY_RANDOM_SHOT];
spr->enable = TRUE;
int i = find_random_enemy_index();
spr->x = sprite[i].x;
spr->y = sprite[i].y + SPRITE_DIM;
spr->color = sprite[i].color;
spr->idx = 4;
timer[TIMER_RANDOM_SHOT].t = 255;
}
static void init_random_shots() {
timer[TIMER_RANDOM_SHOT].t = 255;
timer[TIMER_RANDOM_SHOT].callback = &random_shot;
}
static int music_idx;
static const float MUSIC_FREQUENCIES[] = {
73.42, // D
87.31, // F
82.41, // E
98.00, // G
};
void play_next_music_note() {
play_sound(SQUARE, MUSIC_FREQUENCIES[music_idx], 1.0f, 0.5f, 0.999f);
music_idx++;
music_idx %= 4;
timer[TIMER_MUSIC].t = enemies;
}
static void init_music() {
music_idx = 0;
timer[TIMER_MUSIC].t = enemies;
timer[TIMER_MUSIC].callback = &play_next_music_note;
}
static void init_game() {
ticks = 0;
init_timers();
init_palette();
init_sprites();
lives = 3;
init_player_sprite();
init_enemies();
init_random_shots();
init_music();
}
static void update_enemies() {
// Speed up as # enemies decreases.
// In the original, only one enemy was moved per frame,
// like a Mexican wave. The speed-up was a consequence of that.
if (ticks % enemies == 0) {
bool_t advance = FALSE;
uint8_t xl = 255;
uint8_t xr = 0;
for (int i = 0 ; i < N_ENEMIES; i++) {
if (sprite[i].enable) {
if (sprite[i].x < xl) {
xl = sprite[i].x;
}
if (sprite[i].x > xr) {
xr = sprite[i].x;
}
}
}
if (enemy_dir == DIR_RIGHT && xr > (W - 2*SPRITE_DIM)) {
enemy_dir = DIR_LEFT;
advance = TRUE;
} else if (enemy_dir == DIR_LEFT && xl < SPRITE_DIM) {
enemy_dir = DIR_RIGHT;
advance = TRUE;
}
for (uint8_t j = 0; j < ENEMY_ROWS; j++) {
for (uint8_t i = 0; i < ENEMY_COLS; i++) {
Sprite_t* spr = &sprite[j*ENEMY_COLS+i];
if (spr->idx <= 1) {
spr->idx = (spr->idx + 1) % 2;
}
if (advance) {
spr->y += SPRITE_DIM;
} else {
spr->x += enemy_dir;
}
}
}
}
}
static bool_t check_sprite_collision(int i, int j, int ir, int il) {
const Sprite_t *si, *sj;
si = &sprite[i];
sj = &sprite[j];
return si->enable && sj->enable &&
(si->x+ir >= sj->x)
&& (sj->x+SPRITE_DIM >= si->x+il)
&& (si->y+SPRITE_DIM >= sj->y)
&& (sj->y+SPRITE_DIM >= si->y);
}
static void clear_explosions() {
for (int i = 0; i < N_ENEMIES; i++) {
if (sprite[i].idx == 5) {
sprite[i].enable = FALSE;
}
}
}
static void play_explosion() {
play_sound(SQUARE, 440.0f, 1.0001f, 0.5f, 0.9995f);
}
static void update_player_shot() {
Sprite_t* spr_player = &sprite[SPRITE_PLAYER_SHOT];
if (spr_player->y < SHOT_SPEED) {
spr_player->enable = FALSE;
}
sprite[SPRITE_PLAYER_SHOT].y -= SHOT_SPEED;
for (int i = 0; i < N_ENEMIES; i++) {
if (sprite[i].enable && check_sprite_collision(SPRITE_PLAYER_SHOT, i, 3, 5)) {
sprite[SPRITE_PLAYER_SHOT].enable = FALSE;
sprite[i].idx = 5;
play_explosion();
timer[TIMER_CLEAR_EXPLOSIONS].t = 20;
timer[TIMER_CLEAR_EXPLOSIONS].callback = &clear_explosions;
enemies--;
if (enemies < 1) {
init_enemies();
}
}
}
}
static void update_enemy_shots() {
for (int i = SPRITE_ENEMY_RANDOM_SHOT; i <= SPRITE_ENEMY_RETURN_SHOT; i++) {
Sprite_t *shot = &sprite[i];
if (shot->y >= H - SHOT_SPEED) {
shot->enable = FALSE;
}
shot->y += SHOT_SPEED;
if (shot->enable && check_sprite_collision(i, SPRITE_PLAYER, 3, 5)) {
shot->enable = FALSE;
sprite[SPRITE_PLAYER].idx = 5;
play_explosion();
lives--;
if (lives > 0) {
timer[TIMER_RESTORE_PLAYER].t = 20;
timer[TIMER_RESTORE_PLAYER].callback = &init_player_sprite;
} else {
timer[TIMER_RESTORE_PLAYER].t = 20;
timer[TIMER_RESTORE_PLAYER].callback = &init_game;
}
}
}
}
static void handle_inputs() {
if (joyport & LEFT && sprite[SPRITE_PLAYER].x > 0) {
sprite[SPRITE_PLAYER].x -= 1;
}
if (joyport & RIGHT && sprite[SPRITE_PLAYER].x < W - SPRITE_DIM) {
sprite[SPRITE_PLAYER].x += 1;
}
if (joyport & BUTTON_A && !sprite[SPRITE_PLAYER_SHOT].enable) {
sprite[SPRITE_PLAYER_SHOT].x = sprite[SPRITE_PLAYER].x;
sprite[SPRITE_PLAYER_SHOT].y = 240;
sprite[SPRITE_PLAYER_SHOT].idx = 3;
sprite[SPRITE_PLAYER_SHOT].enable = TRUE;
sprite[SPRITE_PLAYER_SHOT].color = PLAYER_COLOR;
timer[TIMER_RETURN_SHOT].t = 20;
timer[TIMER_RETURN_SHOT].callback = &return_shot;
play_sound(SQUARE, 440.0f, 0.99999f, 0.5f, 0.9995f);
}
}
void handle_timers() {
for (int i = 0; i < N_TIMERS; i++) {
if (timer[i].t) {
timer[i].t--;
if (!timer[i].t) {
timer[i].callback();
}
}
}
}
static void update() {
if (ticks % enemies == 0) { // speed up as # enemies decreases
update_enemies();
}
if (sprite[SPRITE_PLAYER_SHOT].enable) {
update_player_shot();
}
update_enemy_shots();
if (sprite[SPRITE_PLAYER].idx != 5) { // as long as the player isn't exploding
handle_inputs();
}
ticks++;
handle_timers();
}
void draw_sprites() {
for (int i = 0; i < N_SPRITES; i++) {
if (sprite[i].enable) {
const Sprite_t* spr = &sprite[i];
const uint8_t* sprdata = &SPRITE_DATA[spr->idx][0];
for (int y = 0; y < 8; y++) {
uint8_t row = sprdata[y];
for (int x = 0; x < 8; x++) {
if (row & 0x80) {
const int offset = (spr->y+y)*W + spr->x + x;
if (offset < W*H) {
pixels_argb[offset] = FULL_PALETTE[spr->color];
}
}
row <<= 1;
}
}
}
}
}
SDL_GameController *find_controller() {
for (int i = 0; i < SDL_NumJoysticks(); i++) {
if (SDL_IsGameController(i)) {
return SDL_GameControllerOpen(i);
}
}
return 0;
}
void audio_callback(void *userdata, Uint8 *stream, int len)
{
float *buf = (float*)stream;
for (int i = 0; i < len/sizeof(*buf); i++)
{
if (sound.waveform == NONE) {
buf[i] = 0.0f;
} else if (sound.waveform == NOISE) {
buf[i] = sound.a_current * (float)rand() * 2.0 / (float)RAND_MAX - 1.0;
} else if (sound.waveform == SQUARE) {
const float period_samples = 48000.0 / sound.f_current;
const float remainder = fmod((double)sound.i, period_samples);
const float sign = (remainder < period_samples/2.0f) ? -1.0 : 1.0;
buf[i] = sound.a_current * sign;
}
sound.i++;
sound.a_current *= sound.a_decay;
sound.f_current *= sound.f_decay;
}
}
static int quit;
static SDL_Window* window;
static SDL_Renderer* renderer;
static SDL_Surface* surface;
static SDL_Texture* texture;
static SDL_GameController *controller;
static void mainloop() {
SDL_Event e;
if (quit) {
SDL_FreeSurface(surface);
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
#ifdef __EMSCRIPTEN__
emscripten_cancel_main_loop(); /* this should "kill" the app. */
#else
exit(0);
#endif
}
const uint64_t start = SDL_GetPerformanceCounter();
while (SDL_PollEvent(&e)) {
if (e.type == SDL_QUIT) {
quit = 1;
break;
};
switch (e.type) {
case SDL_CONTROLLERBUTTONDOWN:
switch (e.cbutton.button) {
case SDL_CONTROLLER_BUTTON_DPAD_LEFT:
joyport |= LEFT; break;
case SDL_CONTROLLER_BUTTON_DPAD_RIGHT:
joyport |= RIGHT; break;
case SDL_CONTROLLER_BUTTON_A:
joyport |= BUTTON_A; break;
}
break;
case SDL_CONTROLLERBUTTONUP:
switch (e.cbutton.button) {
case SDL_CONTROLLER_BUTTON_DPAD_LEFT:
joyport &= ~LEFT; break;
case SDL_CONTROLLER_BUTTON_DPAD_RIGHT:
joyport &= ~RIGHT; break;
case SDL_CONTROLLER_BUTTON_A:
joyport &= ~BUTTON_A; break;
}
break;
case SDL_CONTROLLERDEVICEADDED:
if (!controller) {
controller = SDL_GameControllerOpen(e.cdevice.which);
}
break;
case SDL_CONTROLLERDEVICEREMOVED:
if (controller
&& e.cdevice.which == SDL_JoystickInstanceID(
SDL_GameControllerGetJoystick(controller)
)) {
SDL_GameControllerClose(controller);
controller = find_controller();
}
break;
}
}
update();
memset(pixels_argb, 0, W*H*sizeof(uint32_t));
draw_sprites();
SDL_RenderClear(renderer);
SDL_UpdateTexture(texture, NULL, pixels_argb, W*4);
SDL_RenderCopy(renderer, texture, 0, 0);
SDL_RenderPresent(renderer);
const uint64_t end = SDL_GetPerformanceCounter();
const float elapsed = (float)(end - start) / (float)SDL_GetPerformanceFrequency();
printf("%2.2f FPS \r", 1.0f/elapsed);
}
extern int main(int argc, char** argv) {
if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_GAMECONTROLLER | SDL_INIT_AUDIO) < 0) {
printf("Failed to initalize SDL: %s\n", SDL_GetError());
return 0;
}
window = SDL_CreateWindow(
"Invader-like",
SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
WINDOW_W, WINDOW_H, SDL_WINDOW_SHOWN
);
if (!window) {
printf("Failed to create SDL window: %s\n", SDL_GetError());
return 0;
}
// cap FPS to VSYNC
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_PRESENTVSYNC);
if (!renderer) {
printf("Failed to create SDL renderer: %s\n", SDL_GetError());
return 0;
}
SDL_RenderSetLogicalSize(renderer, W, H);
SDL_RenderSetIntegerScale(renderer, 1);
texture = SDL_CreateTexture(
renderer, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_STREAMING,
W, H
);
if (SDL_GameControllerEventState(SDL_ENABLE) < 1) {
printf("Failed to enable game controller events: %s\n", SDL_GetError());
return 0;
}
controller = find_controller();
SDL_AudioSpec spec, aspec;
SDL_zero(spec);
spec.freq = 48000;
spec.format = AUDIO_F32;
spec.channels = 1;
spec.samples = 4096;
spec.callback = audio_callback;
spec.userdata = NULL;
int audio;
if ((audio = SDL_OpenAudioDevice(NULL, 0, &spec, &aspec, 0)) <= 0)
{
fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
exit(-1);
}
SDL_PauseAudioDevice(audio, 0); // Start playing, "unpause"
init_game();
quit = 0;
#ifdef __EMSCRIPTEN__
emscripten_set_main_loop(mainloop, 0, 1);
#else
while (1) { mainloop(); }
#endif
return 0;
}