Hi, I'm writing a simple snake game to get the hang of linked lists and things. I haven't coded most of it yet but I am already having two problems.
The first problem is that the "snake" seems to not move at the same speed even though I have tried to do time based movement.
The other problem is if i uncomment this part in the game init:
/*for (x = 0; x <= MAPWIDTH; x++)
for (y = 0; y <= MAPHEIGHT; y++)
map[x][y] = 0;*/
Somthing goes wrong and nothing is displayed in the window at all?!
Anyway, here is my code so far (its nothing special yet). Also if you see anything done in a backwards way could you tell me so I don't go about it the wrong way :) thanks
#include <SDL/SDL.h>
#include <stdio.h>
#include <stdlib.h>
#define MAPWIDTH 40
#define MAPHEIGHT 40
/* Define Booleans */
typedef enum { false, true } bool;
bool one = false;
struct item
{
int x_pos;
int y_pos;
};
struct item apple;
struct part
{
int x_pos, y_pos;
int x_vol, y_vol;
enum Estate {RIGHT, LEFT, UP, DOWN} state;
struct part *next_part; /* Pointer to next part */
};
struct part *first_part = NULL;
struct part *last_part = NULL;
int map[MAPWIDTH][MAPHEIGHT];
/* function predeclarations */
int main(int argc, char *argv[]);
bool game_init();
void game_loop();
void get_input();
void add_apple();
void move_snake(float time_passed);
void draw_apple();
void draw_snake();
void draw_part(struct part *current_part);
void draw_screen();
void game_close();
bool game_running;
float current_time;
SDL_Surface *screen, *sprite_image;
int main(int argc, char *argv[])
{
atexit(game_close);
if (game_init() == false)
exit(1);
while (game_running == true)
game_loop();
}
bool game_init()
{
int x, y;
SDL_Surface *temp;
if (SDL_Init(SDL_INIT_VIDEO) != 0)
{
printf("Unable to initialize SDL\n");
return false;
}
screen = SDL_SetVideoMode(400, 400, 16, SDL_DOUBLEBUF);
if (screen == NULL)
{
printf("Unable to set video mode\n");
return false;
}
SDL_WM_SetCaption("Snake Attempt", NULL);
temp = SDL_LoadBMP("sprites.bmp");
if (temp == NULL)
{
printf("Unable to load picture\n");
return false;
}
SDL_SetColorKey(temp, SDL_SRCCOLORKEY | SDL_RLEACCEL, (Uint16) SDL_MapRGB(temp->format, 0, 0, 0));
sprite_image = SDL_DisplayFormat(temp);
SDL_FreeSurface(temp);
current_time = SDL_GetTicks();
first_part = malloc(sizeof(struct part));
first_part->next_part = NULL;
first_part->x_pos = 200;
first_part->y_pos = 200;
first_part->x_vol = 1;
first_part->y_vol = 0;
first_part->state = RIGHT;
last_part = first_part;
/*for (x = 0; x <= MAPWIDTH; x++)
for (y = 0; y <= MAPHEIGHT; y++)
map[x][y] = 0;*/
add_apple();
game_running = true;
return true;
}
void game_loop()
{
float time_passed, last_time;
last_time = current_time;
current_time = SDL_GetTicks();
time_passed = current_time - last_time;
get_input();
move_snake(time_passed);
draw_screen();
draw_snake();
draw_apple();
SDL_Flip( screen );
}
void get_input()
{
SDL_Event event;
SDL_keysym keysym;
while (SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_QUIT:
game_running = false;
break;
case SDL_KEYDOWN:
keysym = event.key.keysym;
switch(keysym.sym)
{
case SDLK_ESCAPE:
game_running = false;
break;
case SDLK_LEFT:
first_part->x_vol = -1;
first_part->y_vol = 0;
first_part->state = LEFT;
break;
case SDLK_RIGHT:
first_part->x_vol = 1;
first_part->y_vol = 0;
first_part->state = RIGHT;
break;
case SDLK_UP:
first_part->x_vol = 0;
first_part->y_vol = -1;
first_part->state = UP;
break;
case SDLK_DOWN:
first_part->x_vol = 0;
first_part->y_vol = 1;
first_part->state = DOWN;
break;
}
break;
}
break;
}
}
void add_apple()
{
int x, y;
srand( (unsigned)time( NULL ) );
x = rand() % 40;
srand( (unsigned)time( NULL ) );
y = rand() % 40;
apple.x_pos = x;
apple.y_pos = y;
}
void move_snake(float time_passed)
{
time_passed = time_passed / 10;
first_part->x_pos += (first_part->x_vol * time_passed);
first_part->y_pos += (first_part->y_vol * time_passed);
}
void draw_apple()
{
SDL_Rect src, dest;
src.x = 10;
src.y = 0;
src.w = 10;
src.h = 10;
dest.x = apple.x_pos*10;
dest.y = apple.y_pos*10;
dest.w = 10;
dest.h = 10;
SDL_BlitSurface( sprite_image, &src, screen, &dest );
}
void draw_snake()
{
draw_part(first_part);
}
void draw_part(struct part *current_part)
{
SDL_Rect src, dest;
src.x = 0;
src.y = 0;
src.w = 10;
src.h = 10;
dest.x = current_part->x_pos;
dest.y = current_part->y_pos;
dest.w = 10;
dest.h = 10;
SDL_BlitSurface( sprite_image, &src, screen, &dest );
}
void draw_screen()
{
int x, y;
SDL_Rect src, dest;
for (x = 0; x <= MAPWIDTH; x++)
for (y = 0; y <= MAPHEIGHT; y++)
{
printf("X: %d, y: %d\n",x,y);
src.x = 30;
src.y = 0;
src.w = 10;
src.h = 10;
dest.x = x * 10;
dest.y = y * 10;
dest.w = 10;
dest.h = 10;
SDL_BlitSurface( sprite_image, &src, screen, &dest );
}
}
void game_close()
{
SDL_FreeSurface(sprite_image);
SDL_Quit();
}
