SystemParameters.SmallIconWidth returns 16 on any dpi, so how can I check for actual best icon size?

Question

I thought SystemParameters.SmallIconWidth would tell me what's the best size icon for a small icon. However, even when I change the dpi in Settings->Display to 150% the value of SystemParameters.SmallIconWidth remains the same.

Is there a way to check for the best icon size?

(Why I thought that it should change by dpi - this answer, and this one by a user with more than 500k rep.)

Are you sure your DPI changes took effect in your app? You restarted it? — Pm Duda, Jul 12 '21 at 19:33
@PmDuda Yes. I even cleaned the solution and rebuilt to make sure. — ispiro, Jul 12 '21 at 19:33

score 1 · Answer 1 · answered Jul 13 '21 at 19:13

Even if you declare full DPI awareness in the application manifest and/or at run-time, some Windows functions return 96 DPI (or System DPI) values for some reason. You have to pinvoke the new API:

public enum SystemMetric:int { SM_CXSMICON = 49 }
[DllImport("user32.dll")]
static extern int GetSystemMetricsForDpi(SystemMetric smIndex, uint dpi);
[DllImport("user32.dll")]
static extern uint GetDpiForWindow(IntPtr hwnd);

HwndSource source = (HwndSource)HwndSource.FromVisual(this);
IntPtr hWnd = source.Handle;
uint dpi = GetDpiForWindow(hWnd);
int width = GetSystemMetricsForDpi(SM_CXSMICON, dpi);

These functions only exist on Windows 10 update 1607 and later. If you need to support older versions you must manually scale the incorrect DPI value yourself (x = x * dpi / 96) instead of calling these functions.

SystemParameters.SmallIconWidth returns 16 on any dpi, so how can I check for actual best icon size?

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