<?

$DATA_SIZE = 513;
$SEED = 0.0;
$data = array();
$maxY = -1E32;
$minY = 1E32;
mt_srand($DATA_SIZE);
$RAND_MAX = mt_getrandmax();
$data[0][0] = $data[0][$DATA_SIZE-1] = $data[$DATA_SIZE-1][0] = $data[$DATA_SIZE-1][$DATA_SIZE-1] = $SEED;
$h = 200.0;

for ($sideLength = $DATA_SIZE-1; $sideLength >= 2; $sideLength /= 2, $h /= 2.0)     {
          $halfSide = $sideLength/2;
          for($x=0; $x<$DATA_SIZE-1;$x+=$sideLength) {
              ?for($y=0; $y<$DATA_SIZE-1; $y+=$sideLength) {

                    //x,y is upper left corner of the square
                    //calculate average of existing corners
                    $avg = $data[$x][$y] +                     //top left
                    $data[$x+$sideLength][$y]   +                    //top right
                    $data[$x][$y+$sideLength]   +                     //lower left
                    $data[$x+$sideLength][$y+$sideLength];      //lower right
          
                    $avg = $avg / 4.0;

                    //center is average plus random offset in the range (-h, h)
                    $offset = (-$h) + rand() * ($h - (-$h)) / $RAND_MAX;
                    $data[$x+$halfSide][$y+$halfSide] = $avg + $offset;

              ?} //for y
          } // for x
          
          //Generate the diamond values
          //Since diamonds are staggered, we only move x by half side
          //NOTE: if the data shouldn't wrap the x < DATA_SIZE and y < DATA_SIZE
          for ($x=0; $x<$DATA_SIZE; $x+=$halfSide) {
                    for ($y=($x+$halfSide)%$sideLength; $y<$DATA_SIZE; $y+=$sideLength) {
     
                         //x,y is center of diamond
                         //we must use mod and add DATA_SIZE for subtraction 
                         //so that we can wrap around the array to find the corners
     
                         $avg = 
                         $data[($x-$halfSide+$DATA_SIZE)%$DATA_SIZE][$y] +     //left of center
                         $data[($x+$halfSide)%$DATA_SIZE][$y]                    +     //right of center
                         $data[$x][($y+$halfSide)%$DATA_SIZE]                    +     //below center
                         $data[$x][($y-$halfSide+$DATA_SIZE)%$DATA_SIZE];     //above center
     
                         $avg = $avg / 4.0;
     
                         //new value = average plus random offset
                         //calc random value in the range (-h,+h)
                         $offset = (-$h) + rand() * ($h - (-$h)) / $RAND_MAX;
                         $avg = $avg + $offset;
                    
                         //update value for center of diamond
                         $data[$x][$y] = $avg;
     
                         //wrap values on the edges
                         //remove this and adjust loop condition above
                         //for non-wrapping values
                         //if ($x == 0) $data[$DATA_SIZE-1][$y] = $avg;
                         //if ($y == 0) $data[$x][$DATA_SIZE-1] = $avg;
                    } //for y
              ?} //for x
          } //for sideLength
     
     
          //Calculate minY and maxY values
     for ($i = 0; $i<$DATA_SIZE-1; $i++){
          for($j=0; $j<$DATA_SIZE-1; $j++) {
              ?if ($data[$i][$j] > $maxY){
                    $maxY = $data[$i][$j];
              ?}
              ?if ($data[$i][$j] < $minY){
                    $minY = $data[$i][$j];
              ?}
          }
     }
     
     createTerrain();
     
     // start of functions
     function createTerrain(){
        global $DATA_SIZE, $data, $maxY, $minY;
          $px = 0;
          $py = 0;
          $pz = 0;
          $pallete = array();
          // I use a 256px wide image gradient here to represent the colors for elevation
          $im = imagecreatefrompng("map.png");
          for($a = 0;$a<= 256;$a++){
              ?$rgb = imagecolorat($im, $a+1, 1);
              ?$r = ($rgb >> 16) & 0xFF;
              ?$g = ($rgb >> 8) & 0xFF;
              ?$b = $rgb & 0xFF;
              ?$pallete[$a][r] =  $r;
              ?$pallete[$a][g] =  $g;
              ?$pallete[$a][b] =  $b;
          }
          $gd = imagecreatetruecolor($DATA_SIZE, $DATA_SIZE);
          for($x=0; $x < $DATA_SIZE-1; $x++){
                for($y=0; $y < $DATA_SIZE-1; $y++){
                            ??//populate the point struct
                        $px = $x;
                        $py = $data[$x][$y]; // color || height
                        $pz = $y;
                            ??//change range to 0..1
                            ??$py = ($py - $minY) / ($maxY - $minY);
                            ??$py  = floor($py * 255);
                                   $c[0] = $pallete[$py][r];
                                   $c[1] = $pallete[$py][g];
                                   $c[2] = $pallete[$py][b];
                            ??$color = imagecolorallocate($gd, $c[0], $c[1], $c[2]);
                            ??imagesetpixel($gd, round($y),round($x), $color);
                     }
          }
          header('Content-Type: image/png');
          imagepng($gd);
          imagedestroy($gd);
      

}

function html2rgb($color){
    if ($color[0] == '#')
        $color = substr($color, 1);

    if (strlen($color) == 6)
        list($r, $g, $b) = array($color[0].$color[1],
                                 $color[2].$color[3],
                                 $color[4].$color[5]);
    elseif (strlen($color) == 3)
        list($r, $g, $b) = array($color[0].$color[0], $color[1].$color[1], $color[2].$color[2]);
    else
        return false;

    $r = hexdec($r); $g = hexdec($g); $b = hexdec($b);

    return array($r, $g, $b);
}

?>