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// gcc -Wall -O2 sine.c -lvgagl -lvga -lm
#include <vga.h> /* vgalib */
#include <vgagl.h> /* advanced */
#include <math.h> /* sines! */
#include <stdlib.h> /* malloc */
#define VGAMODE G320x200x256
GraphicsContext *physical_screen;
GraphicsContext *virtual_screen;
GraphicsContext *scroll_board;
int main(void)
{
  double a, b, c, d; /* amp, phase, period, shift */
  double aa,bb,cc,dd; /* random values for fun */
  short int p_pos, t_pos; /* pixel & text */
  short int x,y,z; /* y coord, x & z counters */
  char key; /* to wait for keypress */
12345678901234567890123456789012345678901234567890
/* The following text between quotes should be all
   one line. Ignore wrapping */
  char text[] = "....................................Hello happy world and welcome to another episode of Stupid Programming Tricks. This is our scrolltext, well the idea is that you replace this text with your megagreetings list or the number to your pirate BBS. I wrote this one on Conectiva Linux which has the coolest characters but SVGALIB won't print them properly. Please experiment with different values, and try plugging sines into other sines, you can create the most remarkable though often illegible effects. Shout outs to Rigor Mortis (Riggie!), Red Sector, Triad, Fairlight, Quartex, Cynas, DM, RAiD and everyone else who's still alive! Hy3n4 m4s f1n4 out.........................................";
  double textl=sizeof(text); /* text length */
  vga_init(); /* here begin standard inits */
  vga_setmode(VGAMODE); /* we'll allocate our */
  gl_setcontextvga(VGAMODE); /* graphics areas */
  physical_screen=gl_allocatecontext();
  gl_getcontext(physical_screen);
  gl_setcontextvgavirtual(VGAMODE);
  virtual_screen=gl_allocatecontext();
  gl_getcontext(virtual_screen);
  gl_clearscreen(0); /* better clear the screen */
  scroll_board = malloc( (WIDTH/8+1)*8*8*BYTESPERPIXEL);
  gl_setcontextvirtual(WIDTH+8,8,BYTESPERPIXEL,8,scroll_board);
  scroll_board = gl_allocatecontext(); /* ready */
  gl_getcontext(scroll_board);
  gl_setwritemode(FONT_COMPRESSED);
  gl_setfont(8,8,gl_font8x8);
  gl_setfontcolors(0,1);
  gl_setpalettecolor(1,63,13,24);
  srand(time(NULL));
  a=b=c=d=x=y=0; /* amp, phase, period, shift */
  t_pos=p_pos=0; /* text & pixel position */
  aa=rand()%64+16.0; bb=rand()%64+16.0;
  cc=rand()%64+16.0; dd=rand()%128+128.0;
  gl_setcontext(virtual_screen);
  /* main loop */
  for (key=0; key==0; key=vga_getkey()) {
    p_pos += 2; /* adjust speed here */
    /* this redraws the text at each new letter */
    while (p_pos > 8) {
      gl_setcontext(scroll_board);
      gl_writen(0,0,WIDTH/8, &text[t_pos]);
      t_pos++; /* advance text */
      p_pos-=8; /* reset p_pos */
      if (t_pos >= textl)
         t_pos=0; /* reset t_pos */
      gl_setcontext(virtual_screen);
    }
    /* These equations produce readable text
     * but please experiment to witness the
     * potential of illegible sine scrolling
     */
    x+=1; /* a counter for more phase shift */
    for (z=0; z<320; z++) {
      a = 24*sin((z+x)/aa)+24;
      b = 64*sin((x)/bb)+32;
      c = cc*sin((z+x)/cc)+128;
      d = (32-a)*sin((x-z)/dd)+124-a;
      y = a*sin((z+b)/c)+d; /* standard format */
      gl_copyboxfromcontext(scroll_board, z+p_pos,
         0, 1, 8, z, y);
    }
    gl_setpalettecolor(1,31*sin(t_pos/2.0)+32,
       31*sin(t_pos/4.0)+32,
       31*sin(t_pos/8.0)+32);
    gl_copyscreen(physical_screen); /* update */
    gl_clearscreen(0); /* otherwise it smears */
    vga_waitretrace(); /* hold still a*/
  }
  return 0; /* on principle ;) */
}