Cookie settings problem in IE for Facebook iFrame Applications

Recently I was working on a iFrame Facebook application where I faced a problem with cookie in Internet Explorer. I was using cookie to make authenticated API calls from server. This was working fine for all browsers except IE. The cookie was not working with the default cookie settings of IE. As the cookie was getting set in an iframe, IE view it as a third-party cookie and rejects it as the default cookie setting for IE does not allow third-party cookies. The solution for this problem was to have a compact privacy policy on the pages where cookies are needed. Having a compact privacy policy is easy. You need set a compact P3P header on the required pages. I needed to set the following PHP header to solve my problem:

header('P3P:CP="IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT"');

Changing parent window's url from iframe

Sometimes it is needed to change the parent window's url from iframe. It is pretty easy to do with javascript. You need to execute the following javascript from the iframe whenever you want to change parent window's url:

parent.location = "YOUR REDIRECT URL";

That's it.

Transparent area goes black after copying/cropping PNG image using PHP GD library

Recently I was working on a project in which I needed to do some image manipulations using PHP GD library. Specifically I needed to crop some areas from PNG images. I was able to crop the images pretty easily, but there was a problem in the resulting images: the transparent areas were going black which was making the resulting images unusable. To solve this problem I had to do the following:

$cropped_image = ImageCreateTrueColor($crop_width, $crop_height);
imagealphablending( $cropped_image, false );
imagesavealpha( $cropped_image, true );
$transparent = imagecolorallocatealpha($cropped_image, 0, 0, 0, 127);
imagefill($cropped_image, 0, 0, $transparent);
$original_image = ImageCreateFromPNG($image_to_crop);
imagealphablending( $original_image, false );
imagesavealpha( $original_image, true );
ImageCopy($cropped_image, $original_image, 0, 0, $left, $top, $width, $height);
ImagePNG($cropped_image, $save_path);

Here $image is the cropped image. $width and $height are the width and height of the original image respectively. $left and $top are the left and top location of the rectangular portion of the original image which should be cropped. And $save_path is the location where the cropped image should be saved.

Hope this helps someone.

Reset auto_increment value of a MySQL database table after deleting several rows

In a MySQL table with a lot of data, it is very common that last few rows will get deleted frequently. If any column has auto_increment, this will result in a gap in the generated column values. It is very easy to reset the auto_increment value to the correct value which will not result in any gap between the column values. Of course, it is only possible to prevent the gap if the deleted rows were the last few rows of the table. Here is the sql that will reset auto_increment:

ALTER TABLE table_name_to_reset AUTO_INCREMENT=1

That's it. Hope this helps.