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Getting the size of a window's font

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Posted by

Twisol USA (2,257 posts) Bio

Date

Sun 22 Nov 2009 07:36 AM (UTC)

Message

I can't seem to find a way to get the size of an already-loaded font. I don't mean height or width or weight, I want the size that was initially passed to WindowFont() as the fourth parameter. I thought the weight from WindowFontInfo() might be it, but it gave me 400 from a 10pt Lucida Console. Is this possible?

'Soludra' on Achaea

Blog: http://jonathan.com/
GitHub: http://github.com/Twisol

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Posted by

Bast (78 posts) Bio

Date

Reply #1 on Sun 22 Nov 2009 02:21 PM (UTC)

Message

Here is how I get it

self.id = windowid
v = font_id

local size = tonumber(WindowFontInfo(self.id, v, 2)) - tonumber(WindowFontInfo(self.id, v, 3))

Bast

Bast

Scripts: http://github.com/endavis

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Posted by Nick Gammon Australia (23,158 posts) Bio Forum Administrator

Date

Reply #2 on Sun 22 Nov 2009 08:12 PM (UTC)

Amended on Sun 22 Nov 2009 08:53 PM (UTC) by Nick Gammon

Message

Er, let's see. The calculation in the code to convert what you pass into the font height is this:


  int lfHeight = -MulDiv(Size ? Size : 10.0, dc.GetDeviceCaps(LOGPIXELSY), 72);

Now:


#define LOGPIXELSY    90    /* Logical pixels/inch in Y                 */

So, substituting in this line:


/print (GetDeviceCaps (90)) --> 96

Assuming the size is not zero, and replacing we get:


 Height = -MulDiv(Size, 96, 72);

The help for MulDiv says:



MulDiv



The MulDiv function multiplies two 32-bit values and then divides the 64-bit result by a third 32-bit value. The return value is rounded up or down to the nearest integer.

Thus, it is really:


 Height = -Size * 96 / 72

Solving for size given the height (and ignoring the negative sign, see the knowledge base article below for why we do this) gives us:


Size = Height * 72 / 96

ie.


Size = Height * 0.75

See: http://support.microsoft.com/kb/74299

Now using the example here: http://www.gammon.com.au/mushclient/mw_text.htm

We see the following figures:


WindowFont (win, "f", "Trebuchet MS", 28, true, false, false, false) -- define font

width   = WindowTextWidth (win, "f", "Lazy dog yawns")  -- width of text  (270)
height  = WindowFontInfo (win, "f", 1)   -- height of the font  (46)
ascent  = WindowFontInfo (win, "f", 2)   -- ascent (amount above the baseline)  (36)
descent = WindowFontInfo (win, "f", 3)   -- descent (amount below the baseline) (10)
leading = WindowFontInfo (win, "f", 4)   -- leading (space above the highest letter) (9)

According to the Microsoft knowledge base article, the character height, which is what we want, is the font height minus the internal leading. So we need to take WindowFontInfo (win, "f", 1) and subtract WindowFontInfo (win, "f", 4) .

In this particular case it is:


46 - 9 = 37

Now multiply 37 by 0.75 and we get:


37 * 0.75 = 27.75

Round that up and we get back the original 28 which was the font size. Phew!

I'm not sure if the logical pixels per inch would vary from system to system, so you should probably recalculate that, ie.


Size = round ( Height * 72 / GetDeviceCaps (90) )

- Nick Gammon

www.gammon.com.au, www.mushclient.com

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