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.