If you're designing for mobile at all, then retina is meaningless, unless you're disabling page zooming.
Because zoom levels can be anywhere from 0.25, say, to 8x. One user might be viewing part of the page at 2.78x. Another, at 1.3x.
So all this talk of "2x" or "4x", or serving up different files for diffrent resolutions, or aligning to pixel boundaries is quickly becoming meaningless.
That's why scalable solutions like CSS & SVG are a great idea for UI elements.
That said right now often you still need raster graphics (e.g. screenshots) and making sure you provide them in a way that takes zoomability and devices with high pixel density in account makes a lot of sense :)
If you go mobile-first you can avoid many of these mindset pitfalls :)
yep, also regarding the web, as it goes more in the direction of supporting vector images in the browser by using svg files and icons fonts for example, it will hopefully become easier soon.
Because zoom levels can be anywhere from 0.25, say, to 8x. One user might be viewing part of the page at 2.78x. Another, at 1.3x.
So all this talk of "2x" or "4x", or serving up different files for diffrent resolutions, or aligning to pixel boundaries is quickly becoming meaningless.