How windows try to fix it? Does it use other bitmap scaling or doing something else? Why it doesn't work for all dpi-unaware apps? For what apps it works?

The scaling option in Windows 10 does these things automatically on high-resolution displays:

  • Increase the size of fonts
  • Increase the size of icons
  • Upscale the rest of the window according to the computed scaling factor.

The intelligent part of this method is figuring out the scaling factor, which Windows does using the monitor's properties, such as resolution and pixel density (DPI). This is only an educated guess on the part of Windows.

If the window includes images which cannot be upscaled without hurting their display, since images can only be upscaled indefinitely in movies, then the result will not be perfect. This is why there are controls for the individual .exe to specify or disable the automatic scaling, for cases where it fails.

  • And when the option is disabled, Windows scales whole app as a bitmap? – Eugene Maksimov Dec 5 at 7:58
  • When the option is totally disabled, Windows does nothing, and the window will be too small, perhaps unusable. – harrymc Dec 5 at 9:06
  • It seems Windows uses High DPI virtualization in case when the "Let Windows try..." options is switched off. DPI-unaware apps looks blurry, but it scaled on my 4K (175%) monitor. – Eugene Maksimov Dec 5 at 9:34
  • Success depends on the elements that are in the window. Where Windows is in control, such as when using API calls for writing text and drawing lines and rectangles, the results would be perfect. For images, this depends on their type: Vector images such as .eps could be very good, but bit-mapped images may become blurry or pixelated. Windows does a pretty good job in most cases, but not all. – harrymc Dec 5 at 9:56
  • One of the more easily noticeable cases where it doesn't work well is in full-screen applications that do their own UI scaling independent of Windows itself, such as many games (especially ones built on custom rendering engines). Depending on the particular application, it may try to fix things and make it look worse, or Windows may just give up and pester you with notifications about the fact that it gave up. – Austin Hemmelgarn Dec 5 at 20:17

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