[RFC] add radius and sigma to IMG_FILTER_GAUSSIAN_BLUR

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’d 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’s IMG_FILTER_GAUSSIAN_BLUR is not suitable for the job. It maps to <gdImageGaussianBlur>. This method lacks the radius and sigma parameters. Instead it “performs a Gaussian blur of radius 1 on the image” [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 – 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’d 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?

–Felix

[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/SimpleImage.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