3D imaging - depth of field

<?php
function minAngle($line, $p, $threshold, $focus, $depth){
    //---Find the side lengths of the triangle created by the point and the line
    $b = pow($line['x'][1]-$line['x'][2], 2)+pow($line['y'][1]-$line['y'][2], 2)+pow($line['z'][1]-$line['z'][2], 2); //Difference between the two points of the line
    $c = pow($line['x'][1]-$p['x'], 2)+pow($line['y'][1]-$p['y'], 2)+pow($line['z'][1]-$p['z'], 2); //Difference between the start of the line and the point
    $a = pow($p['x']-$line['x'][2], 2)+pow($p['y']-$line['y'][2], 2)+pow($p['z']-$line['z'][2], 2); //difference between the end of the line and the point
    //---Find the angle formed between the ray and the point
    $angle = rad2deg(acos(($b+$c-$a)/(2*sqrt($b)*sqrt($c)))); //cos^(-1)((b^2 + c^2 - a^2) / 2bc), will give the angle between the point an the ray.

    //---Find out how out of focus the point is
    $dif = intval(abs($p['y']-$focus)/$depth);
    if($dif == 0){
        $dif = 1;
    }
    if($angle < $threshold*$dif){
        //---Depending on the angle formed and the level of focus, return the brightness of the ray/pixel.
        $return = str_pad(intval((($threshold*$dif-$angle)/($threshold*$dif))*255), 3, "0", STR_PAD_LEFT);
        echo "test = $return</br>\n";
        return $return;
    }else{
        return '000';
    }
}

//---Variables
$screen_dimensions = array('height' => 300, 'width' => 700); //Do not make this very large as too much memory/time will be used and the program will fail.
$screen_position = array('x' => 0, 'y' => 0, 'z' => 0); //I spose this could be changed, but I haven't bothered with it.

$screen_viewingAngle = 140; //In degrees
$focus = (0.5*$screen_dimensions['width'])/tan(deg2rad(0.5*$screen_viewingAngle)); //The Y frame which will be in focus.
$depth_of_field = 30; //This is kinda like the F-stop on a lens.
$angular_threshold = 2; //This is kinda different, but it's basically the accuracy of the imaging. 0 would be perfect, but would not work.
/* Do not use these yet.
$screen_yaw = 0;
$screen_pitch = 0;
$screen_roll = 0;
*/

/* BEGIN MAIN PROGRAM */

//---Pre-processing variables (inititators of a sort)
$offset['y'] = (0.5*$screen_dimensions['width'])/tan(deg2rad(0.5*$screen_viewingAngle));
$offset['x'] = 0.5*$screen_dimensions['width'];
$offset['z'] = 0.5*$screen_dimensions['height'];

$current['z'] = $offset['z'];
$current['x'] = -$offset['x'];
$cycle = 0;

//---Build points to be displayed
for($i = 0; $i < 36; $i++){
    if($i > 0){
        $current['x'] += $screen_dimensions['width']/5;
    }
    if($current['x'] > $offset['x']){
        $current['x'] = -$offset['x'];
        $current['z'] -= $screen_dimensions['height']/5;
    }

    $points[$i]['x'] = $current['x'];
    $points[$i]['y'] = $offset['y'];
    $points[$i]['z'] = $current['z'];
    print "Z = ".$points[$i]['z'] ." Y = ".$points[$i]['y'] ." X = ".$points[$i]['x'] ."</br>\n";
}
//---Copy these points back a few times
foreach($points as $key => $value){
    $points[$key+36]['x'] = $value['x'];
    $points[$key+36]['z'] = $value['z'];
    $points[$key+36]['y'] = $value['y']+40;
    $points[$key+72]['x'] = $value['x'];
    $points[$key+72]['z'] = $value['z'];
    $points[$key+72]['y'] = $value['y']+80;
    $points[$key+108]['x'] = $value['x'];
    $points[$key+108]['z'] = $value['z'];
    $points[$key+108]['y'] = $value['y']+120;
}

//---Reset '$current' variables
$current['z'] = 0.5*$screen_dimensions['height'];
$current['x'] = -0.5*$screen_dimensions['width'];

//---Begin writing file
unlink("image.ppm"); //file that we will be editing, we are are deleting 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

$print_height = 1+$screen_dimensions['height'];
$print_width = 1+$screen_dimensions['width'];

$startWrite = "P3\n# image.ppm\n$print_width $print_height\n255"; //fomatting the ppm file
fwrite($fh, $startWrite);

//---Begin building rays and printing the file
//These two steps are done at the same time for efficiency, and memory
for($i = 0; $i < ($print_height*$print_width); $i++){
    //---Origin points
    $lines['x'][1] = $screen_position['x'];
    $lines['y'][1] = $screen_position['y'];
    $lines['z'][1] = $screen_position['z'];

    //---Resolve when to move to the next row of pixels
    if($i > 0){
        $current['x']++;
    }
    if($current['x'] > $offset['x']){
        $current['x'] = -$offset['x'];
        $current['z']--;
    }
    //---To points
    $lines['x'][2] = $current['x'];
    $lines['y'][2] = $offset['y'];
    $lines['z'][2] = $current['z'];

    echo $lines['x'][2].", ".$lines['z'][2].", ".$lines['y'][2]."</br> \n";
    if($i%5 == 0){ //basic formatting decides when a new line must be placed
        $Nl = " \n";
    }else{
        $Nl = " ";
    }
    $out = 000;
    foreach($points as $value){
        $colour = minAngle($lines, $value, $angular_threshold, $focus, $depth_of_field);
        if($colour == 255){
            $out = $colour;
            echo "white </br>\n";
            break 1;
        }elseif($colour >= 0 && $colour >= $out){
            $out = $colour;
        }
    }
    $write = "$Nl$out $out $out"; //the line that is to be outputted
    fwrite($fh, $write); //write the pixel to the file.
}
fclose($fh);
?>