CODEWITHSUNDEEP
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Rob
Rob

Reputation: 78748

Windows GDI: horizontal/vertical DPI

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?

Upvotes: 7

Views: 2527

Answers (4)

Rafael Nobre
Rafael Nobre

Reputation: 5131

Its easy for them to be different if the monitor is set up to use a screen resolution ratio that is not the same as the physical screen ratio, such as a 4:3 resolution like 1600x1200 on a 16:9 display.

Upvotes: 0

Orihara
Orihara

Reputation: 309

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.

Upvotes: 7

Head Geek
Head Geek

Reputation: 39888

I've never seen a case where they're different, but the fact that there are two separate calls for it strongly suggests that they might be sometimes.

Upvotes: 0

John Dibling
John Dibling

Reputation: 101494

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!

Upvotes: 1

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