mirror of https://github.com/libsdl-org/SDL
333 lines
9.2 KiB
C
333 lines
9.2 KiB
C
/*
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* Logic implementation of the Snake game. It is designed to efficiently
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* represent in memory the state of the game.
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*
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* This code is public domain. Feel free to use it for any purpose!
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*/
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#define SDL_MAIN_USE_CALLBACKS 1 /* use the callbacks instead of main() */
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#include <SDL3/SDL.h>
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#include <SDL3/SDL_main.h>
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#define STEP_RATE_IN_MILLISECONDS 125
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#define SNAKE_BLOCK_SIZE_IN_PIXELS 24
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#define SDL_WINDOW_WIDTH (SNAKE_BLOCK_SIZE_IN_PIXELS * SNAKE_GAME_WIDTH)
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#define SDL_WINDOW_HEIGHT (SNAKE_BLOCK_SIZE_IN_PIXELS * SNAKE_GAME_HEIGHT)
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#define SNAKE_GAME_WIDTH 24U
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#define SNAKE_GAME_HEIGHT 18U
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#define SNAKE_MATRIX_SIZE (SNAKE_GAME_WIDTH * SNAKE_GAME_HEIGHT)
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#define THREE_BITS 0x7U /* ~CHAR_MAX >> (CHAR_BIT - SNAKE_CELL_MAX_BITS) */
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#define SHIFT(x, y) (((x) + ((y) * SNAKE_GAME_WIDTH)) * SNAKE_CELL_MAX_BITS)
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typedef enum
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{
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SNAKE_CELL_NOTHING = 0U,
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SNAKE_CELL_SRIGHT = 1U,
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SNAKE_CELL_SUP = 2U,
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SNAKE_CELL_SLEFT = 3U,
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SNAKE_CELL_SDOWN = 4U,
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SNAKE_CELL_FOOD = 5U
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} SnakeCell;
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#define SNAKE_CELL_MAX_BITS 3U /* floor(log2(SNAKE_CELL_FOOD)) + 1 */
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typedef enum
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{
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SNAKE_DIR_RIGHT,
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SNAKE_DIR_UP,
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SNAKE_DIR_LEFT,
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SNAKE_DIR_DOWN
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} SnakeDirection;
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typedef struct
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{
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unsigned char cells[(SNAKE_MATRIX_SIZE * SNAKE_CELL_MAX_BITS) / 8U];
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char head_xpos;
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char head_ypos;
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char tail_xpos;
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char tail_ypos;
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char next_dir;
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char inhibit_tail_step;
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unsigned occupied_cells;
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} SnakeContext;
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typedef struct
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{
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SDL_Window *window;
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SDL_Renderer *renderer;
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SDL_TimerID step_timer;
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SnakeContext snake_ctx;
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} AppState;
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SnakeCell snake_cell_at(const SnakeContext *ctx, char x, char y)
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{
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const int shift = SHIFT(x, y);
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unsigned short range;
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SDL_memcpy(&range, ctx->cells + (shift / 8), sizeof(range));
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return (SnakeCell)((range >> (shift % 8)) & THREE_BITS);
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}
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static void set_rect_xy_(SDL_FRect *r, short x, short y)
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{
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r->x = (float)(x * SNAKE_BLOCK_SIZE_IN_PIXELS);
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r->y = (float)(y * SNAKE_BLOCK_SIZE_IN_PIXELS);
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}
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static void put_cell_at_(SnakeContext *ctx, char x, char y, SnakeCell ct)
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{
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const int shift = SHIFT(x, y);
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const int adjust = shift % 8;
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unsigned char *const pos = ctx->cells + (shift / 8);
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unsigned short range;
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SDL_memcpy(&range, pos, sizeof(range));
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range &= ~(THREE_BITS << adjust); /* clear bits */
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range |= (ct & THREE_BITS) << adjust;
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SDL_memcpy(pos, &range, sizeof(range));
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}
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static int are_cells_full_(SnakeContext *ctx)
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{
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return ctx->occupied_cells == SNAKE_GAME_WIDTH * SNAKE_GAME_HEIGHT;
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}
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static void new_food_pos_(SnakeContext *ctx)
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{
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while (true) {
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const char x = (char) SDL_rand(SNAKE_GAME_WIDTH);
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const char y = (char) SDL_rand(SNAKE_GAME_HEIGHT);
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if (snake_cell_at(ctx, x, y) == SNAKE_CELL_NOTHING) {
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put_cell_at_(ctx, x, y, SNAKE_CELL_FOOD);
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break;
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}
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}
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}
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void snake_initialize(SnakeContext *ctx)
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{
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int i;
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SDL_zeroa(ctx->cells);
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ctx->head_xpos = ctx->tail_xpos = SNAKE_GAME_WIDTH / 2;
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ctx->head_ypos = ctx->tail_ypos = SNAKE_GAME_HEIGHT / 2;
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ctx->next_dir = SNAKE_DIR_RIGHT;
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ctx->inhibit_tail_step = ctx->occupied_cells = 4;
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--ctx->occupied_cells;
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put_cell_at_(ctx, ctx->tail_xpos, ctx->tail_ypos, SNAKE_CELL_SRIGHT);
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for (i = 0; i < 4; i++) {
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new_food_pos_(ctx);
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++ctx->occupied_cells;
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}
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}
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void snake_redir(SnakeContext *ctx, SnakeDirection dir)
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{
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SnakeCell ct = snake_cell_at(ctx, ctx->head_xpos, ctx->head_ypos);
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if ((dir == SNAKE_DIR_RIGHT && ct != SNAKE_CELL_SLEFT) ||
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(dir == SNAKE_DIR_UP && ct != SNAKE_CELL_SDOWN) ||
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(dir == SNAKE_DIR_LEFT && ct != SNAKE_CELL_SRIGHT) ||
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(dir == SNAKE_DIR_DOWN && ct != SNAKE_CELL_SUP)) {
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ctx->next_dir = dir;
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}
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}
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static void wrap_around_(char *val, char max)
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{
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if (*val < 0) {
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*val = max - 1;
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} else if (*val > max - 1) {
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*val = 0;
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}
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}
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void snake_step(SnakeContext *ctx)
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{
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const SnakeCell dir_as_cell = (SnakeCell)(ctx->next_dir + 1);
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SnakeCell ct;
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char prev_xpos;
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char prev_ypos;
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/* Move tail forward */
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if (--ctx->inhibit_tail_step == 0) {
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++ctx->inhibit_tail_step;
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ct = snake_cell_at(ctx, ctx->tail_xpos, ctx->tail_ypos);
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put_cell_at_(ctx, ctx->tail_xpos, ctx->tail_ypos, SNAKE_CELL_NOTHING);
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switch (ct) {
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case SNAKE_CELL_SRIGHT:
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ctx->tail_xpos++;
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break;
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case SNAKE_CELL_SUP:
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ctx->tail_ypos--;
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break;
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case SNAKE_CELL_SLEFT:
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ctx->tail_xpos--;
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break;
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case SNAKE_CELL_SDOWN:
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ctx->tail_ypos++;
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break;
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default:
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break;
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}
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wrap_around_(&ctx->tail_xpos, SNAKE_GAME_WIDTH);
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wrap_around_(&ctx->tail_ypos, SNAKE_GAME_HEIGHT);
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}
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/* Move head forward */
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prev_xpos = ctx->head_xpos;
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prev_ypos = ctx->head_ypos;
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switch (ctx->next_dir) {
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case SNAKE_DIR_RIGHT:
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++ctx->head_xpos;
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break;
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case SNAKE_DIR_UP:
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--ctx->head_ypos;
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break;
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case SNAKE_DIR_LEFT:
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--ctx->head_xpos;
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break;
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case SNAKE_DIR_DOWN:
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++ctx->head_ypos;
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break;
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}
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wrap_around_(&ctx->head_xpos, SNAKE_GAME_WIDTH);
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wrap_around_(&ctx->head_ypos, SNAKE_GAME_HEIGHT);
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/* Collisions */
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ct = snake_cell_at(ctx, ctx->head_xpos, ctx->head_ypos);
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if (ct != SNAKE_CELL_NOTHING && ct != SNAKE_CELL_FOOD) {
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snake_initialize(ctx);
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return;
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}
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put_cell_at_(ctx, prev_xpos, prev_ypos, dir_as_cell);
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put_cell_at_(ctx, ctx->head_xpos, ctx->head_ypos, dir_as_cell);
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if (ct == SNAKE_CELL_FOOD) {
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if (are_cells_full_(ctx)) {
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snake_initialize(ctx);
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return;
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}
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new_food_pos_(ctx);
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++ctx->inhibit_tail_step;
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++ctx->occupied_cells;
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}
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}
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static Uint32 sdl_timer_callback_(void *payload, SDL_TimerID timer_id, Uint32 interval)
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{
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/* NOTE: snake_step is not called here directly for multithreaded concerns. */
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SDL_Event event;
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SDL_zero(event);
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event.type = SDL_EVENT_USER;
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SDL_PushEvent(&event);
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return interval;
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}
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static int handle_key_event_(SnakeContext *ctx, SDL_Scancode key_code)
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{
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switch (key_code) {
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/* Quit. */
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case SDL_SCANCODE_ESCAPE:
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case SDL_SCANCODE_Q:
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return SDL_APP_SUCCESS;
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/* Restart the game as if the program was launched. */
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case SDL_SCANCODE_R:
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snake_initialize(ctx);
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break;
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/* Decide new direction of the snake. */
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case SDL_SCANCODE_RIGHT:
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snake_redir(ctx, SNAKE_DIR_RIGHT);
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break;
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case SDL_SCANCODE_UP:
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snake_redir(ctx, SNAKE_DIR_UP);
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break;
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case SDL_SCANCODE_LEFT:
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snake_redir(ctx, SNAKE_DIR_LEFT);
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break;
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case SDL_SCANCODE_DOWN:
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snake_redir(ctx, SNAKE_DIR_DOWN);
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break;
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default:
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break;
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}
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return SDL_APP_CONTINUE;
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}
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SDL_AppResult SDL_AppIterate(void *appstate)
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{
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AppState *as;
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SnakeContext *ctx;
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SDL_FRect r;
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unsigned i;
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unsigned j;
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int ct;
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as = (AppState *)appstate;
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ctx = &as->snake_ctx;
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r.w = r.h = SNAKE_BLOCK_SIZE_IN_PIXELS;
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SDL_SetRenderDrawColor(as->renderer, 0, 0, 0, 255);
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SDL_RenderClear(as->renderer);
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for (i = 0; i < SNAKE_GAME_WIDTH; i++) {
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for (j = 0; j < SNAKE_GAME_HEIGHT; j++) {
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ct = snake_cell_at(ctx, i, j);
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if (ct == SNAKE_CELL_NOTHING)
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continue;
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set_rect_xy_(&r, i, j);
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if (ct == SNAKE_CELL_FOOD)
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SDL_SetRenderDrawColor(as->renderer, 80, 80, 255, 255);
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else /* body */
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SDL_SetRenderDrawColor(as->renderer, 0, 128, 0, 255);
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SDL_RenderFillRect(as->renderer, &r);
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}
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}
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SDL_SetRenderDrawColor(as->renderer, 255, 255, 0, 255); /*head*/
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set_rect_xy_(&r, ctx->head_xpos, ctx->head_ypos);
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SDL_RenderFillRect(as->renderer, &r);
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SDL_RenderPresent(as->renderer);
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return SDL_APP_CONTINUE;
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}
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SDL_AppResult SDL_AppInit(void **appstate, int argc, char *argv[])
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{
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if (!SDL_Init(SDL_INIT_VIDEO)) {
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return SDL_APP_FAILURE;
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}
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AppState *as = SDL_calloc(1, sizeof(AppState));
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*appstate = as;
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if (!SDL_CreateWindowAndRenderer("examples/game/snake", SDL_WINDOW_WIDTH, SDL_WINDOW_HEIGHT, 0, &as->window, &as->renderer)) {
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return SDL_APP_FAILURE;
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}
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snake_initialize(&as->snake_ctx);
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as->step_timer = SDL_AddTimer(STEP_RATE_IN_MILLISECONDS, sdl_timer_callback_, NULL);
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if (as->step_timer == 0) {
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return SDL_APP_FAILURE;
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}
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return SDL_APP_CONTINUE;
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}
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SDL_AppResult SDL_AppEvent(void *appstate, SDL_Event *event)
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{
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SnakeContext *ctx = &((AppState *)appstate)->snake_ctx;
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switch (event->type) {
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case SDL_EVENT_QUIT:
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return SDL_APP_SUCCESS;
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case SDL_EVENT_USER:
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snake_step(ctx);
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break;
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case SDL_EVENT_KEY_DOWN:
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return handle_key_event_(ctx, event->key.scancode);
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}
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return SDL_APP_CONTINUE;
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}
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void SDL_AppQuit(void *appstate)
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{
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if (appstate != NULL) {
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AppState *as = (AppState *)appstate;
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SDL_RemoveTimer(as->step_timer);
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SDL_DestroyRenderer(as->renderer);
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SDL_DestroyWindow(as->window);
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SDL_free(as);
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}
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}
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