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Date: Wed, 28 Sep 2016 10:09:54 +0200
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Subject: [RFC] add radius and sigma to IMG_FILTER_GAUSSIAN_BLUR
From: mail@felixniklas.de (Felix Niklas)

Hey there,

this is my first time on here and I want to start out by saying how =
thankful I am for your work. Thank you for working on php. Thank you for =
pushing this language further.

tl;dr: I=E2=80=99d like to add the parameters radius and sigma to the =
$filtertype IMG_FILTER_GAUSSIAN_BLUR by switching the underlying libgd =
method from <gdImageGaussianBlur> (accepts no parameters) to =
<gdImageCopyGaussianBlurred> (accepts these parameters).

Recently I wanted to replace a css blur filter with pre-processed images =
that get blurred on the server in order to improve the =
scroll-performance in the browser. I had to realise that imagefilter=E2=80=
=99s IMG_FILTER_GAUSSIAN_BLUR is not suitable for the job. It maps to =
<gdImageGaussianBlur>. This method lacks the radius and sigma =
parameters. Instead it =E2=80=9Cperforms a Gaussian blur of radius 1 on =
the image=E2=80=9D [1]. Imagine using a brush to blur an image: radius 1 =
is like using a tiny tiny brush. What would you use to blur more =
intensely? A big brush. But the option to switch is not there. =
SimpleImage.php tries to overcome this by blurring with the tiny brush =
over and over [2]. The thing is =E2=80=93 the tiny brush is inevective. =
If you want a big blur you need a big brush. And it can be achieved by =
binding to <gdImageCopyGaussianBlurred> instead of =
<gdImageGaussianBlur>.

I think I can write the patch for the method [3]. The added parameters =
would have to get checked so I=E2=80=99d have to look into how =
<zend_parse_parameters> works. <gdImageGaussianBlur> returns a boolean, =
<gdImageCopyGaussianBlurred> [4] returns a copy of the image instead. If =
<gdImageCopyGaussianBlurred> fails it returns NULL. So the code handling =
the return value would have to handle a NULL return instead of an =
integer > 0 return.

Thoughts?

=E2=80=93Felix

[1] gd_filter.c <gdImageGaussianBlur> =
https://github.com/libgd/libgd/blob/master/src/gd_filter.c#L709
[2] SimpleImage.php <blur> =
https://github.com/claviska/SimpleImage/blob/master/src/abeautifulsite/Sim=
pleImage.php#L174
[3] gd.c <php_image_filter_gaussian_blur> =
https://github.com/php/php-src/blob/master/ext/gd/gd.c#L4392
[4] gd_filter.c <gdImageCopyGaussianBlurred> =
https://github.com/libgd/libgd/blob/master/src/gd_filter.c#L922=