Windows GDI：水平/垂直DPI

Question

When obtaining the DPI for the screen under Windows (by using ::GetDeviceCaps) will the horizontal value always be the same as the vertical? For example:

HDC dc = ::GetDC(NULL);
const int xDPI = ::GetDeviceCaps(dc, LOGPIXELSX);
const int yDPI - ::GetDeviceCaps(dc, LOGPIXELSY);
assert(xDPI == yDPI);
::ReleaseDC(NULL, dc);

Are these values ever different?

Answer 1

It's possible for it to be different, but that generally only applies to printers. It can be safely assumed that the screen will always have identical horizontal and vertical DPIs.

Answer 2

I have never seen them be different, but on this MSDN page I see a comment that suggests that they might be:

   int nHorz = dc.GetDeviceCaps(LOGPIXELSX);
   int nVert = dc.GetDeviceCaps(LOGPIXELSY);

   // almost always the same in both directions, but sometimes not!

Answer 3

我从来没有见过他们不同的情况，但事实上有两个单独的呼吁强烈暗示他们有时可能。

Answer 4

如果将显示器设置为使用与物理屏幕比率不同的屏幕分辨率，例如在16：9显示器上为1600x1200的4：3分辨率，则它们很容易变得不同。