The typical geek reaction to this problem can be summed up in one word. "Vectors!" Text scales nicely because the letter shapes are defined by a series of parameterized equations (vectors) that can be "solved" at any resolution, yielding smooth curves as the characters change size. So, the geek thinking goes, why not draw everything with vectors? Scrollbars, menus, buttons, icons, everything! Problem solved!
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These are all tractable problems, but at a certain point the approach bears reexamining. The goal is to be "scalable," not necessarily to be able to scale indefinitely. There's little need for a perfectly rendered, exquisitely detailed "OK" button to fill an entire 30-inch screen, for example.
Declaration of Resolution Independence