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Independent monitor scaling varies by main display selection


I'm using a new Surface Book connected to two external displays. The Surface Book's main display is high-DPI and set to 200% UI scaling. The external displays are 40-inch 4K monitors running at 100% UI scaling.

Windows 10's independent scaling ratio feature mostly works, but has at least a few clunky behaviors. One of the most bothersome is that the rendering behavior varies based on the main display's characteristics.

If the main display is low (normal) DPI, the high-DPI display often will show a nearest-neighbor (rough) scaling of the UI—even with modern/Metro applications. Not great, but workable.

Worse, though: if the main display is high DPI, the low-DPI display appears to use a rendering algorithm that is "render at 200% and then resize back down to 100%."

The following illustrates the difference. Both of these screen grabs are from the low/normal-DPI display.

First is the normal-DPI display when it is the main display:


That look great! Exactly how it should look. (Note my 4K monitor is using an atypical RGB-pixel arrangement so the Cleartype may look wrong to you, but it looks great here.)

Next is the normal-DPI display when the high-DPI display is marked as the main display:


The UI elements are the same size, but everything appears as if it were rendered at 200% and then scaled back down to 100%. In fact, most jarring to my eye is that the vertical edge of the window is 2px thick when the horizontal edge is 1px thick. This is basically unusable to me since it looks like everything is blurred.

Bottom line: On my Surface Book, I mark one of my external displays as the main display to make it look clean. However, as you might imagine, since Windows' management of application windows is a bit, uh, chaotic when the display configuration changes, I have a lot of rearrangement work to do any time I detach and re-attach the Surface Book clipboard (tablet).

Does anyone have a secret incantation to make the normal-DPI displays render in their native 100% without that scaling effect, even when the high-DPI display is marked as main?