how to draw semi-transparent rectangle in php?

问题

Here is an example what I would like to do:

Here is the result:

function red_rectangle($img_src,$x1,$y1,$x2,$y2,$tr = 50)
{
    // Load image
    $img = imagecreatefromjpeg($img_src);
    // Transparent red
    $red = imagecolorallocatealpha($img, 255, 0, 0, $tr);
    // Draw a white rectangle
    imagefilledrectangle($img, $x1, $y1, $x2, $y2, $red);
    // Save the image (overwrite)
    imagejpeg($img, $img_src);
    imagedestroy($img);
}

回答1:

You need to use http://php.net/manual/en/function.imagefilledrectangle.php, passing a color created with http://www.php.net/manual/en/function.imagecolorallocatealpha.php.

As you can see, the example for http://php.net/manual/en/function.imagefilledrectangle.php is pratically what to you want to do.

回答2:

function red_rectangle($img_src,$x1,$y1,$x2,$y2,$tr = 100)
{
// Load image
$img = imagecreatefromjpeg($img_src);

// Transparent red
$red = imagecolorallocatealpha($img, 255, 0, 0, $tr);

// Draw a white rectangle
imagefilledrectangle($img, $x1, $y1, $x2, $y2, $red);


// Don't forget to output a correct header
header('Content-Type: image/jpg');

// Save the image (overwrite)
imagejpeg($img);
imagedestroy($img);
}
$img_src = 'test.jpg';
$x1= 500;
$y1= 450;
$x2 = 370;
$y2=180;
red_rectangle($img_src,$x1,$y1,$x2,$y2);

来源：https://stackoverflow.com/questions/8443699/how-to-draw-semi-transparent-rectangle-in-php