Icon: Assume default icon size is always 16x16

[rozmansi]

win.GetSystemMetricsForDpi() ignores dpi parameter prior Windows 10. It
returns 16x16, or 24x24, or 32x32 depending on "zoom" set by user.
Assume the default small icon size is always 16x16 at 96dpi.

[zx2c4]

Is this a safe assumption to make?

Isn't the point of the system metrics to query it from the OS?

[rozmansi]

Isn't the point of the system metrics to query it from the OS?

While Windows 10 have the GetSystemMetricsForDPI() that returns accurate icon size for 96dpi, the Windows 7 and 8 will have the DPI embedded into GetSystemMetrics() result.

We can't use win.GetSystemMetricsForDPI() as it fallbacks to GetSystemMetrics() and we wouldn't know if the value returned is the icon size with or without DPI conversion.

The best way to get this metrics reliably is to do the GetSystemMetricsForDPI() and GetSystemMetrics() dance ourselves:

if GetSystemMetricsForDPI() is available {
   // This is Windows 10.
   return GetSystemMetricsForDPI(SM_CXSMICONSIZE, 96);
}
// This is Windows 7 or 8: GetSystemMetrics() returns values in screen DPI.
return GetSystemMetrics(SM_CXSMICONSIZE) / screenDPI * 96

[zx2c4]

Can you just hack lxn/win so that its fallback implementation successfully /screenDPI*96?

[zx2c4]

This seems better: lxn/win#99

[rozmansi]

Indeed, the better approach is to fix GetSystemMetricsForDpi() in lxn/win instead.