scrolling_tile.c

#include "scrolling_tile.h"

static SDL_Surface *tile = NULL;
static double pos_x, pos_y, speed_x, speed_y;
static Uint32 last_scroll;

static void scrolling_map_exit(void)
{
  SDL_FreeSurface(tile);
}
int init_scrolling_map(void)
{
  if(!(tile = load_image("gfx/tile.png")))
    return 0;
  
  reset_scrolling_map();
  
  atexit(scrolling_map_exit);
  return 1;
}
void reset_scrolling_map(void)
{
  pos_x = 0;
  pos_y = 0;
  speed_x = 0;
  speed_y = 0;
  
  last_scroll = SDL_GetTicks();
}

void set_scrolling_speed(const double x, const double y)
{
  speed_x = x;
  speed_y = y;
}
double get_scrolling_speed_x(void)
{
  return speed_x;
}
double get_scrolling_speed_y(void)
{
  return speed_y;
}

void increase_scrolling_speed(const double x, const double y)
{
  speed_x += x;
  speed_y += y;
}
void scroll_map(void)
{
  pos_x += speed_x * (SDL_GetTicks() - last_scroll);
  pos_y += speed_y * (SDL_GetTicks() - last_scroll);
  
  last_scroll = SDL_GetTicks();
}
void blit_scrolling_map(SDL_Surface *dst)
{
  SDL_Rect tile_dst, shift_dst;
  
  for(tile_dst.y = -tile->h; tile_dst.y <= dst->h; tile_dst.y += tile->h)
  {
    for(tile_dst.x = -tile->w; tile_dst.x <= dst->w + tile->w; tile_dst.x += tile->w)
    {
      shift_dst = tile_dst;
      shift_dst.x += (int)pos_x % tile->w;
      shift_dst.y += (int)pos_y % tile->h;
      
      SDL_BlitSurface(tile, NULL, dst, &shift_dst);
    }
  }
}
void extend_scrolling_map_timestamp(const Uint32 time)
{
  last_scroll += time;
}