DPI scaling not working properly in Game build on macOS

Development Programming & Scripting
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Hi! I’m building a pure Slate-based application using Unreal Engine 5.5 on macOS, and I’ve encountered a persistent DPI-related issue in the Game (standalone) build.

In Unreal Editor, everything works perfectly — the DPI scale is correctly set to 2.0 on my Retina display, and the UI looks crisp and sharp.

However, in the standalone Game build the initial dpi_scale returned from FPlatformApplicationMisc::GetDPIScaleFactorAtPoint(0, 0) was always 1.0, and everything looked blurry and downscaled.

To force DPI into working, I did the following:

  1. Enabled “Enable High DPI in Game” in the project settings → it added bAllowHighDPIInGameMode=True to DefaultEngine.ini

  2. Called FSlateApplication::Get().InitHighDPI(true); in my GameInstance before creating any windows

  3. Set NSHighResolutionCapable = YES in Info.plist

After that, the dpi_scale finally became 2.0, which is what I expected. But new problems appeared:

  • The reported screen size from FSlateApplication::Get().GetDisplayMetrics(...) was now only 1512 x 982 instead of the actual 3024 x 1964

  • As a result, the application windows were initialized at half the intended size, even though dpi_scale == 2.0

  • Manually resizing the window with the mouse revealed that the UI was correctly Retina-scaled, but the initial sizing and layout were wrong

This leads me to think DPI is only partially working — the rendering is correct, but Slate still uses logical resolution where it shouldn’t, or the metrics are mismatched.

How can I ensure that DPI is fully initialized, and that window sizing and layout reflect Retina resolution properly in standalone Game builds on macOS?

Thanks in advance!