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This article is about setting the attributes of a snake, followed by the previous article (V ).

 

It is easy to set the speed of a snake, as long as it is not a negative number.

void SNK_SetSnakeSpeed(Snake *snake, int speed){    if (snake != 0) snake->speed = SDL_abs(speed);}

 

It is complicated to set the direction of a snake. Anyone who has ever played the Snake knows that when the snake moves forward, it cannot turn backward; when it moves left, it cannot turn to the right. So I have to make such judgments.

void SNK_SetSnakeDirection(Snake *snake, int direction){    if (snake != 0 && (direction & (SNAKE_UP | SNAKE_DOWN | SNAKE_LEFT | SNAKE_RIGHT)))    {        if (snake->direction & (SNAKE_UP | SNAKE_DOWN))        {            if (direction & (SNAKE_LEFT | SNAKE_RIGHT))                snake->direction = direction;        }        else        {            if (direction & (SNAKE_UP | SNAKE_DOWN))                snake->direction = direction;        }    }}

This ensures that the direction is correct and the turns are correct.

 

Finally, set the snake color, so there is nothing to say.

void SNK_SetSnakeColor(Snake *snake, Uint8 r, Uint8 g, Uint8 b, Uint8 a){    if (snake != 0)    {        snake->color.r = r;        snake->color.g = g;        snake->color.b = b;        snake->color.a = a;    }}

 

At this point, the implementation code of the snake is finished. This is the core of the entire game. Next, we will create a beautiful interface.

 

The complete source code for the snk-snake.c file is as follows:

#include "snk-snake.h"#define INIT_SNAKE(world, size, x, y)                                       \    snake->world = (world);                                                 \    snake->x = (SDL_abs(x) > (world)->w) ? 0 : SDL_abs(x);                  \    snake->x = (size) ? ((snake->x / SDL_abs(size)) * SDL_abs(size)) : 0;   \    snake->y = (SDL_abs(y) > (world)->h) ? 0 : SDL_abs(y);                  \    snake->y = (size) ? ((snake->y / SDL_abs(size)) * SDL_abs(size)) : 0;   \    snake->size = (size) ? SDL_abs(size) : 0;                               \    snake->color.r = snake->color.g = snake->color.b = snake->color.a = 0;  \    snake->speed = 0;                                                       \    snake->length = 1;                                                      \    snake->direction = SNAKE_UP;                                            \    snake->body = 0;#define MOVE_SNAKE(body) do {                                               \    switch ((body)->direction)                                              \    {                                                                       \        case SNAKE_UP:   (body)->y -= snake->size; break;                   \        case SNAKE_DOWN: (body)->y += snake->size; break;                   \        case SNAKE_LEFT: (body)->x -= snake->size; break;                   \        case SNAKE_RIGHT:(body)->x += snake->size; break;                   \    }                                                                       \} while (0)#define APPEND_BODY(last, body) do {                                        \    if ((last)->direction & (SNAKE_UP | SNAKE_DOWN)) {                      \        (body)->x = (last)->x;                                              \        if ((last)->direction & SNAKE_UP)                                   \            (body)->y = (last)->y + snake->size;                            \        else                                                                \            (body)->y = (last)->y - snake->size;                            \    } else {                                                                \        if ((last)->direction & SNAKE_LEFT)                                 \            (body)->x = (last)->x + snake->size;                            \        else                                                                \            (body)->x = (last)->x - snake->size;                            \        (body)->y = (last)->y;                                              \    }                                                                       \    (body)->direction = (last)->direction;                                  \    (body)->next = (snake->body != 0) ? snake->body : 0;                    \    snake->body = (body);                                                   \    ++snake->length;                                                        \} while (0)#define REMOVE_BODY(body) do {                                              \    snake->body = (body)->next;                                             \    SDL_free(body);                                                         \    (body) = snake->body;                                                   \} while (body)Snake * SNK_CreateSnake(World *world, int size, int x, int y){    Snake *snake;    if (world == 0) return 0;    if ((snake = (Snake *)SDL_malloc(sizeof(Snake))) == 0) return 0;    INIT_SNAKE(world, size, x, y);    SNK_GrowSnake(snake);    return snake;}void SNK_DestroySnake(Snake *snake){    struct Body *body;    if (snake != 0)    {        if ((body = snake->body)) REMOVE_BODY(body);        SDL_free(snake);        snake = 0;    }}void SNK_MoveSnake(Snake *snake){    struct Body *body;    if (snake != 0)    {        MOVE_SNAKE(snake);        for (body = snake->body; body; body = body->next)        {            MOVE_SNAKE(body);            body->direction = (body->next != 0) ? body->next->direction : snake->direction;        }    }}void SNK_DrawSnake(Snake *snake){    SDL_Rect rect;    struct Body *body;    if (snake != 0)    {        rect.x = snake->x;        rect.y = snake->y;        rect.w = rect.h = snake->size;        if (((snake->world != 0) ? (snake->world->render != 0) : 0))        {            SDL_SetRenderDrawColor(snake->world->render,                                   snake->color.r, snake->color.g,                                   snake->color.b, snake->color.a);            SDL_RenderDrawRect(snake->world->render, &rect);            for (body = snake->body; body; body = body->next)            {                rect.x = body->x;                rect.y = body->y;                SDL_RenderDrawRect(snake->world->render, &rect);            }        }    }}void SNK_GrowSnake(Snake *snake){    struct Body *body;    if (snake != 0)    {        if ((body = (struct Body *)SDL_malloc(sizeof(struct Body))) == 0) return;        if (snake->body == 0)        {            APPEND_BODY(snake, body);        }        else        {            APPEND_BODY(snake->body, body);        }    }}int SNK_HasIntersection(Snake *snake, SDL_Rect rect){    SDL_Rect bodyrect;    struct Body *body;    if (snake != 0)    {        bodyrect.w = bodyrect.h = snake->size;        for (body = snake->body; body; body = body->next)        {            bodyrect.x = body->x;            bodyrect.y = body->y;            if (SDL_HasIntersection(&bodyrect, &rect) != 0)                return 1;        }    }    return 0;}int SNK_GetSnakeStatus(Snake *snake){    SDL_Rect headrect;    if (((snake != 0) ? (snake->world != 0) : 0))    {        headrect.w = (snake->x > 0 && snake->x < snake->world->w);        headrect.h = (snake->y > 0 && snake->y < snake->world->h);        if (headrect.w && headrect.h)        {            headrect.x = snake->x;            headrect.y = snake->y;            headrect.w = headrect.h = snake->size;            if (SNK_HasIntersection(snake, headrect) != 0)                return SNAKE_DIED;            return SNAKE_MOVABLE;        }        else        {            switch (snake->direction)            {            case SNAKE_UP:                headrect.x = (snake->y > 0);                break;            case SNAKE_DOWN:                headrect.x = ((snake->y + snake->size) < snake->world->h);                break;            case SNAKE_LEFT:                headrect.x = (snake->x > 0);                break;            case SNAKE_RIGHT:                headrect.x = ((snake->x + snake->size) < snake->world->w);                break;            }            return ((headrect.x != 0) ? SNAKE_MOVABLE : 0);        }    }    return 0;}void SNK_SetSnakeSpeed(Snake *snake, int speed){    if (snake != 0) snake->speed = SDL_abs(speed);}void SNK_SetSnakeDirection(Snake *snake, int direction){    if (snake != 0 && (direction & (SNAKE_UP | SNAKE_DOWN | SNAKE_LEFT | SNAKE_RIGHT)))    {        if (snake->direction & (SNAKE_UP | SNAKE_DOWN))        {            if (direction & (SNAKE_LEFT | SNAKE_RIGHT))                snake->direction = direction;        }        else        {            if (direction & (SNAKE_UP | SNAKE_DOWN))                snake->direction = direction;        }    }}void SNK_SetSnakeColor(Snake *snake, Uint8 r, Uint8 g, Uint8 b, Uint8 a){    if (snake != 0)    {        snake->color.r = r;        snake->color.g = g;        snake->color.b = b;        snake->color.a = a;    }}

In the macro INIT_SNAKE, snake-> x and snake-> y Repeat twice, mainly to align the location of the snake and the size of the snake.

APPEND_BODY is used to append a linked list node, and sets snake-> body to always point to the end of the snake to improve the efficiency of appending nodes.