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21 years ago
here is a function that helps you create arrows...

<?php
function get_arrowheads ($x1, $y1, $x2, $y2, $arrhead, $arrang) {
    $debug = false;
    
    define("INFINITE", 'INFINITE');
    if (($x2-$x1)==0) {
        if ($y1 == 0) {
            $slope = 0;
        } else {
            $slope = INFINITE;
        }
    } else {
        $slope = -($y2-$y1)/($x2-$x1);
    }

    //$slope = number_format($slope, 2, '.','');
    if ($slope == 'INFINITE') {
        $ang = 90;
    } else {
        $ang = atan ($slope);
        $ang = ($ang * 180)/pi();
    }
    //$ang = number_format($ang, 2, '.', '');
    //echo ($ang);
    //exit;

    //convert the angle
    $arrang1 = ($ang - $arrang);
    $arrangdeg1 = ($ang - $arrang);
    //echo ($arrang1);exit;
    $arrang1 = ($arrang1*pi())/180;

    $arrang2 = ($ang + $arrang);
    $arrangdeg2 = ($ang + $arrang);
    $arrang2 = ($arrang2*pi())/180;
    //echo ($arrang1);

    $arx1 = (floor(cos($arrang1)*$arrhead));
    $ary1 = (floor(sin($arrang1)*$arrhead));
    $arx2 = (floor(cos($arrang2)*$arrhead));
    $ary2 = (floor(sin($arrang2)*$arrhead));
    if ($debug) {
        echo ("Values of arx1.. before add/sub</br>");
        echo ("$arx1,$ary1&nbsp;&nbsp;&nbsp;$arx2,$ary2</br>");
    }
    if ($ang==0) {
        if ($x2 > $x1) {
            $arx1 = $x2 - $arx1;    $ary1 = $y2 - $ary1;
            $arx2 = $x2 - $arx2;    $ary2 = $y2 - $ary2;
        } elseif ($x2 < $x1) {
            $arx1 = $x2 + $arx1;    $ary1 = $y2 - $ary1;
            $arx2 = $x2 + $arx2;    $ary2 = $y2 - $ary2;
        }
    }
    if ($ang > 0 && $ang < 90) {
        if (($x2 > $x1) && ($y2 < $y1)) {
            $arx1 = $x2 - $arx1;    $ary1 = $y2 + $ary1;
            $arx2 = $x2 - $arx2;    $ary2 = $y2 + $ary2;
        } elseif (($x2 < $x1) && ($y2 > $y1)) {
            $arx1 = $x2 + $arx1;    $ary1 = $y2 - $ary1;
            $arx2 = $x2 + $arx2;    $ary2 = $y2 - $ary2;
        }
    }
    if ($ang==90) {
        if (($y2 > $y1)) {
            $arx1 = $x2 - $arx1;    $ary1 = $y2 - $ary1;
            $arx2 = $x2 - $arx2;    $ary2 = $y2 - $ary2;
        } elseif (($y2 < $y1)) {
            $arx1 = $x2 - $arx1;    $ary1 = $y2 + $ary1;
            $arx2 = $x2 - $arx2;    $ary2 = $y2 + $ary2;
        }
    }
    if ($ang > -90 && $ang < 0) {
        if (($x2 > $x1) && ($y2 > $y1)) {
            $arx1 = $x2 - $arx1;    $ary1 = $y2 + $ary1;
            $arx2 = $x2 - $arx2;    $ary2 = $y2 + $ary2;
        } elseif (($x2 < $x1) && ($y2 < $y1)) {
            $arx1 = $x2 + $arx1;    $ary1 = $y2 - $ary1;
            $arx2 = $x2 + $arx2;    $ary2 = $y2 - $ary2;
        }
    }

    if ($debug) {
        echo ("Angle of line is (".$ang*180/pi().")</br>");
        echo ("Angle of line1 is $arrangdeg1</br>");
        echo ("Angle of line2 is $arrangdeg2</br>");
        echo ("$arx1,$ary1&nbsp;&nbsp;&nbsp;$x2,$y2</br>");
        echo ("$arx2,$ary2&nbsp;&nbsp;&nbsp;$x2,$y2");
        exit;
    }
    
    $array_arrows = array (
                    'x1' =>$arx1,
                    'y1' => $ary1,
                    'x2' => $arx2,
                    'y2' => $ary2
                    );
    return $array_arrows;

}

$x1 = 200; $y1 = 200;
$x2 = 400; $y2 = 100;
$arrhead = 15; //10px
$arrang = 10; //10 deg

$ar_arrws = get_arrowheads ($x1, $y1, $x2, $y2, $arrhead, $arrang);

$im  = imagecreate (400, 400); 
$w   = imagecolorallocate ($im, 255, 255, 255); 
$red = imagecolorallocate ($im, 255, 0, 0); 

//creates the base line
imageline ($im, $x1, $y1, $x2, $y2, $green);
imageline ($im, $x1+1, $x2+1, $y1+1, $y2+1, $red);
imageline ($im, $x2, $y2, $ar_arrws['x1'], $ar_arrws['y1'], $green);
imageline ($im, $x2, $y2, $ar_arrws['x2'], $ar_arrws['y2'], $green);

?>
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