how to draw semi-transparent rectangle in php?

Question

Here is an example what I would like to do:

Here is the result:

<

Answer 1

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);