PHP project - Line segment projection.

<?php
//-----Functions
function dot($u,$v){                                //// u and v are 2 vectors
  return $u[0] * $v[0] + $u[1] * $v[1] + $u[2] * $v[2];
}

function norm($v){
  return sqrt(dot($v,$v));
}

function subvect($x, $y){
  $r = array(3);
  $r[0] = $x[0] - $y[0];
  $r[1] = $x[1] - $y[1];
  $r[2] = $x[2] - $y[2];
  return $r;
}

function dist($u, $v){
  return norm(subvect($u,$v));
}

 function dist3DSegment($line1, $line2){ //$line1 and $line2 are two line segments, each with two defining points. (x1, y1, z1)-(x2, y2, z2)
  $eplison =  0.0000001; //Grrr... wrote 'epsilon' everywhere because of this.

  $u = array(3);
  $v = array(3);
  $w = array(3);

  $u[0] = $line1["x2"] - $line1["x1"];
  $u[1] = $line1["y2"] - $line1["y1"];
  $u[2] = $line1["z2"] - $line1["z1"];

  $v[0] = $line2["x2"] - $line2["x1"];
  $v[1] = $line2["y2"] - $line2["y1"];
  $v[2] = $line2["z2"] - $line2["z1"];

  $w[0] = $line1["x2"] - $line2["x1"];
  $w[1] = $line1["y2"] - $line2["y1"];
  $w[2] = $line1["z2"] - $line2["z1"];

  $a = dot($u, $u);
  $b = dot($u, $v);
  $c = dot($v, $v);
  $d = dot($u, $w);
  $e = dot($v, $w);
  $D = ($a*$c) - ($b*$b);

  // compute the line parameters of the two closest points
  if($D < $eplison){
    $sN = 0.0;
    $sD = 1.0;
    $tN = $e;
    $tD = $c;
  }else{ // get the closest points on the infinite lines
    $sN = ($b*$e - $c*$d);
    $tN = ($a*$e - $b*$d);
      if ($sN < 0.0){       // sc < 0 => the s=0 edge is visible
        $sN = 0.0;
        $tN = $e;
        $tD = $c;
      }else if ($sN > $sD){  // sc > 1 => the s=1 edge is visible
        $sN = $sD;
        $tN = $e + $b;
        $tD = $c;
      }
  }

  if($tN < 0.0){           // tc < 0 => the t=0 edge is visible
    $tN = 0.0;
    // recompute sc for this edge
    if ((-1*$d) < 0.0){
      $sN = 0.0;
    }else if ((-1*$d) > $a){
      $sN = $sD;
    }else{
      $sN = (-1*$d);
      $sD = $a;
    }
  }

    else if ($tN > $tD) {      // tc > 1 => the t=1 edge is visible
        $tN = $tD;
        // recompute sc for this edge
        if (((-1*$d) + $b) < 0.0){
          $sN = 0;
        }else if (((-1*$d) + $b) > $a){
          $sN = $sD;
        }else {
          $sN = ((-1*$d) + $b);
          $sD = $a;
        }
    }
    // finally do the division to get sc and tc
    if (abs($sN) < $epsilon){
    $sc = 0.0;
    }else $sc = $sN / $sD;
    if (abs($tN) < $epsilon){
    $tc = 0.0;
    }else $tc = $tN / $tD;

 // get the difference of the two closest points
    $dP = array(3);
    $dP[0] = $w[0] + ($sc * $u[0]) - ($tc * $v[0]);  // = S1(sc) - S2(tc)
    $dP[1] = $w[1] + ($sc * $u[1]) - ($tc * $v[1]);
    $dP[2] = $w[2] + ($sc * $u[2]) - ($tc * $v[2]);

    return norm($dP);   // return the closest distance
}

//-----Being main program

$maxDrawDist = 40; //Max draw dist is the maximum Z distance that will be made observable. This is required as the test 'rays' are no longer rays, but line segments.
//For some reason, I have to set maxDrawDist to the same distance as the farthest Z value of the line I am trying to project. It seems that this value bisects the line.
$amountOfRainbows = 1; //SET TO ZERO IF YOU DON'T WANT ANY RAINBOWS!!! (Seems to only be able to make one rainbow at the moment, I'll look into this later)

$line1 = array("x1" => -60, "y1" => 60, "z1" => 40, "x2" => 60, "y2" => -60, "z2" => 40); //my input line
$projScr = array("x1" => -200, "y1" => 100, "z1" => 30, "x2" => 200, "y2" => -100, "z2" => 30); //dimensions and location of the screen.
$OriPos = array("x" => 0, "y" => 0, "z" => 0); //origin position is the position that is being used for the projector.

$totalTests = abs(($projScr['y1'] - $projScr['y2']) * ($projScr['x1'] - $projScr['x2'])); //how many pixel tests are to be run
$curPy = $projScr['y1']; //pre-loop definitions (not entirely necessary)
$curPx = $projScr['x1']; //pre-loop definitions (not entirely necessary)

for($i = 0; $i < $totalTests; $i++){
  if($i > 0) $curPx++;
  if($curPx == 0){ $testPx = 1;}else{$testPx = $curPx;}
  if($testPx%(abs($projScr['x2'])) == 0 && $i > 0){ $curPx = $projScr['x1']; $curPy += -1;} //if at the end of the line, move to the next row (Y+1) (super-dooper ugly line of code, but I decided I want to write it in one line and that's final.)
  $curPz = $projScr['z1']; //'Current Position Z' is constant as I haven't concerned myself with changing the angle of the screen, yet.

  $k = abs($maxDrawDist / $curPz); //MAX DRAW DIST MAKES THE RAY LONGER. xD
  $Longz = $curPz * $k; //MAKES EVERYTHING IN THE SAME RATIO
  $Longx = $curPx * $k; //MAKES EVERYTHING IN THE SAME RATIO
  $Longy = $curPy * $k; //MAKES EVERYTHING IN THE SAME RATIO

  $line2 = array("x1" => $curPx, "y1" => $curPy, "z1" => $curPz, "x2" => $Longx, "y2" => $Longy, "z2" => $Longz);

  $dist = dist3DSegment($line1, $line2);

  //Rainbows n' stuff
  if($amountOfRainbows > 0){
    if($dist < 0.0001) $dist = 0.0001;
    $intensity[$i] = abs(floor( (1785 * $amountOfRainbows) / $dist));
  }else{
    if($dist < 1) $dist = 1;
    $intensity[$i] = abs(floor(255 / $dist));
  }
}

//-----Start writing file (THIS BIT OF THE CODE IS SIMPLY A FILE PRINTER, NOTHING INTERESTING TO SEE HERE)

unlink("image.ppm"); //file that we will be editting, we are are delteing the file so we have a clean file to work on
$fh = fopen("image.ppm", 'a+'); //creates the image file that we will be editting and opens the file for appending

$width = abs($projScr['x1'] - $projScr['x2']);
$height = abs($projScr['y1'] - $projScr['y2']);

$startWrite = "P3\n# image.ppm\n".$width." ".$height."\n255\n";
fwrite($fh, $startWrite);

$CurPx = 0;
foreach($intensity as $spec){
    $CurPx++;
    if($CurPx%5 == 0){ //Checks if it has to make a new line (max line length in PPM files is 70 characters)
        $Nl = "\n";
    }else{
        $Nl = " ";
    }

    //Creating lighting and colouring for individual pixels.
  if($amountOfRainbows > 0){
    //if($spec > (1785 * $amountOfRainbows) ) $spec = (1785 * $amountOfRainbows); //THIS LINE ISN'T VERY IMPORTANT WHEN USING MODULUS IN THE NEXT LINE
    if($spec%1785 == 0 && $spec != 0){
      $spec = $spec%1785;
      }
      //----MAKING A RAINBOW (WITH SOME EXPERT RAINBOW MAPPING, THIS OCCURS)

      $modulus = intval($spec)%255;
      if($modulus == 0){ $modulus = 255;}

      if(intval($spec) <= 255){ $red = 255; $green = 0; $blue = 0;} //Using rainbows to see different shades of black isn't very useful, because if distance is large, it will all appear the same shade of red.
      if(intval($spec) > 255 && intval($spec) <= 510){ $red = 255; $green = 0; $blue = $modulus;}
      if(intval($spec) > 510 && intval($spec) <= 765){ $red = 255 - $modulus; $green = 0; $blue = 255;}
      if(intval($spec) > 765 && intval($spec) <= 1020){ $red = 0; $green = $modulus; $blue = 255;}
      if(intval($spec) > 1020 && intval($spec) <= 1275){ $red = 0; $green = 255; $blue = 255 - $modulus;}
      if(intval($spec) > 1275 && intval($spec) <= 1530){ $red = $modulus; $green = 255; $blue = 0;}
      if(intval($spec) > 1530 && intval($spec) <= 1785){ $red = 255; $green = 255 - $modulus; $blue = 0;}

      //----END MAKING RAINBOW

      $pad = ""; //RED CHANEL
      $dots = 3 - strlen($red);
      for($i = 0; $i < $dots; $i++){ //The padding is so the file is written correcting. Zeros must be included.
        $pad = $pad."0";
      }
      $red = $pad.$red;

      $pad = ""; //GREEN CHANNEL
      $dots = 3 - strlen($green);
      for($i = 0; $i < $dots; $i++){
        $pad = $pad."0";
      }
      $green = $pad.$green;

      $pad = ""; //BLUE CHANNEL
      $dots = 3 - strlen($blue);
      for($i = 0; $i < $dots; $i++){
        $pad = $pad."0";
      }
      $blue = $pad.$blue;

      $write = $red." ".$green." ".$blue.$Nl;
      fwrite($fh, $write);
    }else{ //IF NO RAINBOWS
      if($spec > 255) $spec = 255;
      $pad = "";
      $dots = 3 - strlen($spec);
      for($i = 0; $i < $dots; $i++){
        $pad = $pad."0";
      }
      $spec = $pad.$spec;
      $write = $spec." ".$spec." ".$spec.$Nl;
      fwrite($fh, $write);
    }
}
fclose($fh);
?>