winapi - GetSystemMetrics() returns wrong value for SM_CXSCREEN

Question

I've run into an interesting problem. At least in Vista, getSystemMetrics(SM_CXSCREEN) returns an incorrect value when the desktop DPI settings aren't set at 100%. For example, I tried 150% in a 1366x768 screen and getSystemMetrics() returns 911 instead of 1366 (and 1366 / 1.5 ~ 911)

According to the MSDN, getSystemMetrics(SM_CXSCREEN) returns pixels, so I thought this value wouldn't be affected by the DPI settings - but it is. So is there a safer way to find out the true, unscaled screen resolution?

Answer 1

A program must tell the operating system that it is DPI-aware to get the true resolution when you go past 125%. That's best done with a manifest, as explained in this MSDN Library article.