I have to correct you there, because it is only a half-truth: applications such as browsers render the fonts and vector images at the highest pixel resolution possible on a retina/4K screen. Photoshop is unable to emulate this behaviour, and zooming in 200% causes the pixels to be doubled for both vector graphics and text. In Photoline and Illustrator, for example, the pixel grid can be turned off, which renders bitmaps as bitmaps (pixels), and vector art and text are rendered at the native screen resolution, even at 200% zoom - which is the "correct" behaviour. The situation is exacerbated by the limitations of smart objects: even IF a 2X resolution version is nested in a SO, it is still rendered visually at the lower resolution of the master document. Photoshop's preview on a retina screen does not reflect the actual rendering of such an image in a browser. In applications such as Photoline, InDesign, and Illustrator this is a non-issue: the designer works at the "interpreted" lower resolution (for example, 1024px width), and the high resolution image content is displayed nicely at true resolution on a retina screen. Not so, unfortunately, in Photoshop. Thus the only solution is to design at double the resolution in Photoshop, which is not exactly ideal either. As a Photoshop user, the front-end designer has two work-arounds available to her/him: 1) work at the original interpreted resolution, zoom in at 200%, but with the caveat that vector, text, and 2x resolution content in SOs is rendered at a twice as low resolution compared to what browsers and apps on retina screens render, or 2) work at double the resolution, zoom out at 50%, which means all measurements must be doubled, and thereby losing the physical dimensions relationship with the platforms one designs for. In the end the proposed 200% work-around in Photoshop is only halfway usable for screen, web, and front-end designers dealing with retina screen design. Arguably I would say Photoshop is rather awkward in the first place for screen-based (GUI) design work, and I would urge anyone still doing this type of work in Photoshop to look for alternatives. Especially now that retina screens have become the norm (well, at least for Mobile). Even Illustrator and InDesign are "better" choices in my opinion - and for many other reasons as well. My advice: do your bitmap prep work in Photoshop, and the GUI/front-end design in other design applications which honour the interpreted resolution and vector/text/2x image rendering. Even apps such as Macaw and PineGrow are better propositions for web work (Muse might become usable after the devs add responsive layout design) - especially since they render the result directly in a browser-based environment. You truly get what you see in those cases. And having a code base for free is incredibly useful as well.
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