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我使用imagefilledpolygon畫（PHP）GIF圖像上的箭頭，我想使黑色概述的箭頭創建多邊形輪廓。我首先創建箭頭三角形，然後在該三角形的箭頭效果的基礎繪製厚線。爲GIF圖像
一個解決方案，我認爲是創建兩個三角箭頭，第一個是黑色的，比第一（創建大綱效果）略大，但我不知道如何去的是數學。
任何幫助將是偉大的！
代碼來創建箭頭（頭和尾）：
function arrow($img, $x1, $y1, $x2, $y2, $alength, $awidth, $color) {
$distance = sqrt(pow($x1 - $x2, 2) + pow($y1 - $y2, 2));
$dx = $x2 + ($x1 - $x2) * $alength/$distance;
$dy = $y2 + ($y1 - $y2) * $alength/$distance;
$k = $awidth/$alength;
$x2o = $x2 - $dx;
$y2o = $dy - $y2;
$x3 = $y2o * $k + $dx;
$y3 = $x2o * $k + $dy;
$x4 = $dx - $y2o * $k;
$y4 = $dy - $x2o * $k;
imagelinethick($img, $x1, $y1, $dx, $dy, $color,3);
return imagefilledpolygon($img, array($x2, $y2, $x3, $y3, $x4, $y4), 3, $color);
}
這個函數被調用的箭頭線（僅供參考）：
function imagelinethick($image, $x1, $y1, $x2, $y2, $color, $thick = 1)
{
/* this way it works well only for orthogonal lines
imagesetthickness($image, $thick);
return imageline($image, $x1, $y1, $x2, $y2, $color);
*/
if ($thick == 1) {
return imageline($image, $x1, $y1, $x2, $y2, $color);
}
$t = $thick/2 - 0.5;
if ($x1 == $x2 || $y1 == $y2) {
return imagefilledrectangle($image, round(min($x1, $x2) - $t), round(min($y1, $y2) - $t), round(max($x1, $x2) + $t), round(max($y1, $y2) + $t), $color);
}
$k = ($y2 - $y1)/($x2 - $x1); //y = kx + q
$a = $t/sqrt(1 + pow($k, 2));
$points = array(
round($x1 - (1+$k)*$a), round($y1 + (1-$k)*$a),
round($x1 - (1-$k)*$a), round($y1 - (1+$k)*$a),
round($x2 + (1+$k)*$a), round($y2 - (1-$k)*$a),
round($x2 + (1-$k)*$a), round($y2 + (1+$k)*$a),
);
imagefilledpolygon($image, $points, 4, $color);
return imagepolygon($image, $points, 4, $color);
}