function pdf_arrow ($pdfobj, $x1, $y1, $x2, $y2, $dashed) {
// This function will draw, stroke, and fill a line
// from (x1,y1) to (x2,y2) with an arrowhead defined
// by $headangle (in degrees) and $arrowlength.
// If $dashed is nonzero, a dashed line is drawn.
// REQUIRES: find_angle
$headangle = 20;
$arrowlength = 20;
list ($angle, $slope) = find_angle($x1, $y1, $x2, $y2);
pdf_moveto($pdfobj, $x2, $y2);
// Find the two other points of the arrowhead
// using $headangle and $arrowlength.
$xarrow1 = $x2+cos(deg2rad(180+$angle+$headangle/2))*$arrowlength;
$yarrow1 = $y2+sin(deg2rad(180+$angle+$headangle/2))*$arrowlength;
$xarrow2 = $x2+cos(deg2rad(180+$angle-$headangle/2))*$arrowlength;
$yarrow2 = $y2+sin(deg2rad(180+$angle-$headangle/2))*$arrowlength;
// Draw two legs of the arrowhead, close and fill
pdf_lineto($pdfobj, $xarrow1, $yarrow1);
pdf_lineto($pdfobj, $xarrow2, $yarrow2);
pdf_closepath($pdfobj);
pdf_fill($pdfobj);
// Find the point bisecting the short side
// of the arrowhead. This is necessary so
// the end of the line doesn't poke out the
// beyond the arrow point.
$x2line = ($xarrow1+$xarrow2)/2;
$y2line = ($yarrow1+$yarrow2)/2;
// Now draw the "body" line of the arrow
if ($dashed != 0) {
pdf_setdash($pdfobj,5,5);
}
pdf_moveto($pdfobj, $x1, $y1);
pdf_lineto($pdfobj, $x2line, $y2line);
pdf_stroke($pdfobj);
}