当文本以数字开头时，imagettfbbox 计算出错误的矩形

Question

问题是，当使用 imagettfbbox 计算文本尺寸时，当输入文本以数字开头时返回的矩形太小。这是我的代码：

$fontSize = 150;
$font = "font/courier_new.ttf";
$text = $_GET["text"];

//Determine font dimensions
$bbox = imagettfbbox($fontSize, 0, $font, $text);   
$bbox["width"]=  abs($bbox[4]-$bbox[0]);
$bbox["height"]= abs($bbox[5]-$bbox[1]);

$im = imagecreatetruecolor($bbox["width"], $bbox["height"]);

echo "<b>Image size:</b>\n";
print_r($bbox);

// This part makes transparent background
imagesavealpha($im, true);
$bg = imagecolorallocatealpha($im, 254, 254, 254,127); 
$text_color= imagecolorallocate($im, 0, 0, 0);
imagealphablending($im, false);
imagefilledrectangle($im, 0, 0, imagesx($im), imagesy($im), $bg );
imagealphablending($im, true); 


header("X-Img-Size: ".$bbox["width"]."x".$bbox["height"]."");

imagettftext($im, $fontSize, 0, 0, $bbox["height"], $text_color, $font, $text);

// This is output    
header("Content-Type: text/html");  
ob_start();
imagepng($im);
$image_data = ob_get_contents();
ob_end_clean();
imagedestroy($im);

echo "<img src=\"data:image/png;base64,".base64_encode($image_data)."\" />";

Online test here

这些是我针对不同的输入文本得到的结果：

我该如何解决？

Answer 1

问题是误会造成的。 imagettfbbox 的值还定义了 你必须从哪里开始绘制 - 通常这些坐标甚至是负数。我一直假设您可以从 [0, 0] 坐标开始。事实并非如此，绘图坐标可以为负值。

此函数也在评论中提到，源自 PHP.net 用户贡献，计算起始坐标以及宽度和高度（在相关代码中是正确的）。

// Source: http://php.net/manual/en/function.imagettfbbox.php#75407
function imagettfbboxextended($size, $angle, $fontfile, $text) {
    /*this function extends imagettfbbox and includes within the returned array
    the actual text width and height as well as the x and y coordinates the
    text should be drawn from to render correctly.  This currently only works
    for an angle of zero and corrects the issue of hanging letters e.g. jpqg*/
    $bbox = imagettfbbox($size, $angle, $fontfile, $text);

    //calculate x baseline
    if($bbox[0] >= -1) {
        $bbox['x'] = abs($bbox[0] + 1) * -1;
    } else {
        //$bbox['x'] = 0;
        $bbox['x'] = abs($bbox[0] + 2);
    }

    //calculate actual text width
    $bbox['width'] = abs($bbox[2] - $bbox[0]);
    if($bbox[0] < -1) {
        $bbox['width'] = abs($bbox[2]) + abs($bbox[0]) - 1;
    }

    //calculate y baseline
    $bbox['y'] = abs($bbox[5] + 1);

    //calculate actual text height
    $bbox['height'] = abs($bbox[7]) - abs($bbox[1]);
    if($bbox[3] > 0) {
        $bbox['height'] = abs($bbox[7] - $bbox[1]) - 1;
    }

    return $bbox;
}

但绘图时必须使用此函数给出的x和y坐标：

imagettftext($im, $fontSize, 0, $bbox["x"], $bbox["y"], $text_color, $font, $text);

当文本以数字开头时，imagettfbbox 计算出错误的矩形

imagettfbbox calculates wrong rectangle when text begins with number

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imagettftext