Create square-flags directory and a script to generate them

[waldyrious]

Also add a gallery of square flags (rendered here).

Background

In commit db685c546c, the strategy used to make the flags circular was changed from a <mask> to a border-radius style attribute. I assumed this would allow users to dynamically change the shape of the flags using just CSS to edit the border radius (perhaps even animating it!).

However, it doesn't seem to be possible to change the border radius of SVG files at embed time in an HTML file. (Expand this for details of what I tried.)

> I tried various approaches: copying the ``, `

[waldyrious]

By the way, in response to the following note from a comment in #11:

One drawback to this approach is of course that applying custom masks (such as a squircle) is no longer possible. A squircle can (hypothetically) be made with pure CSS, but it's far more verbose than just using a clipPath.

We can actually use circles, ellipses, and arbitrary polygons using the clip-path property in CSS — see https://bennettfeely.com/clippy/ for a bunch of examples.

What's more, even a squircle is kind of possible, by approximating the shape using SVG-defined curves! For example, see the relatively simple geometry by @nklunder in https://codepen.io/nklunder/pen/ZrxbZO. Unfortunately it doesn't seem to be possible to define the clip-path as an inline SVG document (encoded as a data URL), like this:

clip-path: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='0' height='0'%3E%3Cdefs%3E%3CclipPath id='squircle' clipPathUnits='objectBoundingBox'%3E%3Cpath d='M .5,0 C .1,0 0,.1 0,.5 0,.9 .1,1 .5,1 .9,1 1,.9 1,.5 1,.1 .9,0 .5,0 Z'/%3E%3C/clipPath%3E%3C/defs%3E%3C/svg%3E");

But the separate SVG element as shown in the CodePen link above is certainly viable! And besides, we can always use a linear-segment approximation to a squircle by using a polygon, which does allow a pure-CSS approach to implementing a squircle clip shape, like this:

clip-path: polygon(50% 0%, 36.37% 0.5%, 30.53% 1.19%, 25.31% 2.19%, 20.68% 3.54%, 16.6% 5.27%, 13% 7.42%, 10% 10%, 7.42% 13%, 5.27% 16.6%, 3.54% 20.68%, 2.19% 25.31%, 1.19% 30.53%, 0.5% 36.37%, 0% 50%, 0.5% 63.63%, 1.18% 69.47%, 2.18% 74.69%, 3.53% 79.32%, 5.26% 83.32%, 7.4% 86.87%, 9.98% 89.87%, 12.98% 92.45%, 16.53% 94.59%, 20.53% 96.32%, 25.16% 97.67%, 30.38% 98.67%, 36.22% 99.35%, 49.85% 99.85%, 63.48% 99.35%, 69.32% 98.67%, 74.54% 97.67%, 79.17% 96.31%, 83.17% 94.57%, 86.72% 92.42%, 89.72% 89.83%, 92.3% 86.83%, 94.44% 83.28%, 96.17% 79.28%, 97.52% 74.64%, 98.52% 69.42%, 99.2% 63.58%, 100% 50%, 99.50% 36.37%, 98.82% 30.53%, 97.82% 25.31%, 96.46% 20.68%, 94.74% 16.6%, 92.59% 13%, 90% 10%, 86.95% 7.42%, 83.4% 5.27%, 79.32% 3.54%, 74.69% 2.19%, 69.48% 1.19%, 63.64% 0.5%, 50% 0%);

The difference between this and the SVG shape with the curves is barely noticeable:

(SVG clip-path on the left, polygon approximation on the right)

[waldyrious]

Regarding what I wrote above:

I've tested these square icons, and the border-radius now properly applies to all four methods of embedding the images (<svg>, <img>, <object> and <embed>)! :tada:

...I just pushed a new commit tweaking the square flags to merely have no border-radius attribute, rather than explicitly setting it to zero. That allows even inlined versions of these flags to be restyled using border-radius in CSS without resorting to the !important hack :)