oldschool twister effect

twister.c

#include <stdio.h>
#include <math.h>
#include <SDL/SDL.h>

#define LOCK_SURFACE(A) if (SDL_MUSTLOCK(A)) if (SDL_LockSurface(A) < 0) { printf("%s\n", SDL_GetError()); exit(1); }
#define UNLOCK_SURFACE(A) if (SDL_MUSTLOCK(A)) SDL_UnlockSurface(A);

#define ANGLE(A) (A) * M_PI / 180.

#define W   320
#define H   200
#define BPP 24

#define BAR_W   100
#define BAR_X   W / 2


float aa = 1;

SDL_Surface*    video;
Uint8*          keys;

void inline put_pixel(SDL_Surface *s, int x, int y, Uint32 col)
{
  LOCK_SURFACE(s);

  Uint8 *p = (Uint8 *) s->pixels + (s->pitch * y) + x * s->format->BytesPerPixel;

  *(Uint32 *)p = col;

  UNLOCK_SURFACE(s);
}

Uint32 inline get_pixel(SDL_Surface *s, int x, int y)
{
  Uint8 *p = (Uint8 *) s->pixels + (s->pitch * y) + x * s->format->BytesPerPixel;

  return *(Uint32 *)p;
}

void inline draw_hline(SDL_Surface *s, int x, int y, int len, Uint32 col)
{
  LOCK_SURFACE(s);
  Uint8 *p = (Uint8 *) s->pixels + (s->pitch * y) + x * s->format->BytesPerPixel;
  int i;

  for (i = 0; i < len; i++) {
    Uint8 r, g, b;

    *(Uint32 *)p = col;
    p += s->format->BytesPerPixel;
  }

  UNLOCK_SURFACE(s);
}

void draw_twister()
{
  int x, y;

  float amp = sin(aa / 60.) * M_PI + M_PI * 2; /* near the zero, higher frequency. (we don't want too much of that) */
  float ang = sin(aa / 40.) * M_PI + M_PI ; /* [0 -> M_PI * 2] */

    for (y = 0; y < video->h; y++)
    {
      int x1, x2, x3, x4;

      x1 = BAR_W / 2 + BAR_W / 2 * sin(ANGLE(y / amp) + ang);
      x2 = BAR_W / 2 + BAR_W / 2 * sin(ANGLE(y / amp) + ang + M_PI / 2);
      x3 = BAR_W / 2 + BAR_W / 2 * sin(ANGLE(y / amp) + ang + M_PI);
      x4 = BAR_W / 2 + BAR_W / 2 * sin(ANGLE(y / amp) + ang + M_PI + M_PI / 2);

      if (x1 < x2) draw_hline(video, BAR_X + x1, y, x2 - x1, 0xff);
      if (x2 < x3) draw_hline(video, BAR_X + x2, y, x3 - x2, 0xff << 8);
      if (x3 < x4) draw_hline(video, BAR_X + x3, y, x4 - x3, 0xff << 16);
      if (x4 < x1) draw_hline(video, BAR_X + x4, y, x1 - x4, 0xffff00);
    }
}


int main(int argc, char *argv[])
{
  if (SDL_Init(SDL_INIT_EVERYTHING) < 0) { printf("%s\n", SDL_GetError()); exit(1); }
  if ((video = SDL_SetVideoMode(W, H, BPP, SDL_DOUBLEBUF | SDL_HWSURFACE | SDL_HWACCEL)) == NULL) { printf("%s\n", SDL_GetError()); exit(1); }

  keys = SDL_GetKeyState(NULL);

  while(!keys[SDLK_ESCAPE]) 
  {
    SDL_FillRect(video, NULL, 0);
    SDL_PumpEvents();

    draw_twister();

    SDL_Flip(video);

    aa++;

    SDL_Delay(1000/30.);
  }


  SDL_Quit();

  return 0; 
}