Fossil → src/timeline.c → bg_to_fg()

/*
** Change the RGB background color given in the argument in a foreground
** color with the same hue.
*/
/*
  Modifications:

  * check if color values contain non-hex chars, and return default value if so
  * allow color values in shorthand hex triplet form #HHH
  * ensure each color component is between 0 and 255 to avoid #HHHHHHHH output
  * return default color values #000000 (for white background) or #FFFFFF (for
    black background) for all non-hex triplet color values (!)
  * moved whiteFg initialization up so it is ready when jumping to default

  I tried to follow the Fossil coding style guidelines, and I have some open
  questions:

  * is strchr() allowed for hex-digit testing?
    if( strchr("0123456789abcdefABCDEF",zIn[i])==0 ) ...
  * which is the preferred storage format for the default color values, string
    or sqlite3_snprintf() with constant numeric data?
*/
static const char *bg_to_fg(const char *zIn){
  int nIn; /* length of zIn */
  int i;
  unsigned int x[3];
  unsigned int mx = 0;
  static int whiteFg = -1;
  static char zRes[10];
  /* Initialization moved here so it is ready when jumping to default_fg */
  if( whiteFg<0 ) whiteFg = skin_detail_boolean("white-foreground");
  nIn = strlen( zIn );
  if(( nIn!=7 && nIn!=4 ) || zIn[0]!='#' )
    goto default_fg;
  /* Testing for non-hex chars, is strchr() allowed? */
  for (i=1; i<nIn; i++){
    if(( zIn[i]<'0' || zIn[i]>'9' ) &&
       ( zIn[i]<'a' || zIn[i]>'f' ) &&
       ( zIn[i]<'A' || zIn[i]>'F' ))
      goto default_fg;
  }
  zIn++;
  if ( nIn==4 ){
    for(i=0; i<3; i++){
      x[i] = hex_digit_value(zIn[0])*17;
      zIn++;
      if( x[i]>mx ) mx = x[i];
    }
  }else{
    for(i=0; i<3; i++){
      x[i] = hex_digit_value(zIn[0])*16 + hex_digit_value(zIn[1]);
      zIn += 2;
      if( x[i]>mx ) mx = x[i];
    }
  }
  if( whiteFg ){
    /* Make the color lighter */
    static const unsigned int t = 215;
    if( mx<t ) for(i=0; i<3; i++) x[i] += t - mx;
  }else{
    /* Make the color darker */
    static const unsigned int t = 128;
    if( mx>t ) for(i=0; i<3; i++) x[i] -= mx - t;
  }
  /* Make sure each color component is between 0 and 255 */
  for (i=0; i<3; i++)
    x[i] = x[i]<0 ? 0 : x[i]>255 ? 255 : x[i];
  sqlite3_snprintf(sizeof(zRes),zRes,"#%02x%02x%02x",x[0],x[1],x[2]);
  return zRes;
default_fg:
  /* By default, set to black for white background, and vice versa */
  if( whiteFg )
    memcpy(zRes,"#FFFFFF",8);
    /* sqlite3_snprintf(sizeof(zRes),zRes,"#%02x%02x%02x",255,255,255); */
  else
    memcpy(zRes,"#000000",8);
    /* sqlite3_snprintf(sizeof(zRes),zRes,"#%02x%02x%02x",0,0,0); */
  return zRes;
}