What is wx.Font pointSize?

Peter Damoc wrote:
> Hi list,
> 
> I'm playing a little bit with fonts recently and I'm
trying to 
> understand what is pointSize.
> I mean, I look at an image like this one:
> http://en.wikipedia.org/wiki/Image:Typography_Line_T
erms.svg
> and I ask myself. "What is pointSize?"  I
thought it should be 
> Ascent+Descent?

Points is a typography metric that comes from the old days
of the hand 
cranked printing press.  A point is 1/72 of an inch, which
means that if 
you are setting type into a press that is 72 points then the
height of 
the type glyphs you are putting in the press is about one
inch high.

How that translates into pixels on a screen or dots on a
page depends on 
the DPI of the device, and whether or not the OS actually
uses that DPI 
or just assumes something like 96dpi for everything. 
(cough-microsoft-cough!)

> 
> Zooming in and measuring the actual size of the text
doesn't help. It 
> looks like the size is only the distance between
baseline and cap size 
> with the drawing having an offset equal to the distance
between cap size 
> line and ascent line.

You can't assume that points equals pixels, because most of
the time 
they won't.  Also keep printing in mind.  If you have a 14
point font on 
screen, let's say that it is using text that is about 20
pixels high. 
If you now run that through to the printer then in order to
have the 
scaling right so you can actually read the text, then it
could easily be 
as much as a few hundred dots high on the page, depending on
the dpi of 
the printer.

You can however create a font based on pixel size instead of
points. 
There is an alternate constructor called
wx.FontFromPixelSize that takes 
a wx.Size as the first parameter instead of an integer. 
It's fairly new 
so I haven't used it myself, but I have been told that the
different 
platforms deal with the width part of that size object
differently, so 
you'll probably want to experiment with it a bit to get a
feel for how 
it works.

BTW, here is some other nearly useless trivia: a point is
1/12 of a pica.

-- 
Robin Dunn
Software Craftsman
http://wxPython.org  Java
give you jitters?  Relax with wxPython!


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Pajak, Tom (GE Healthcare) wrote:
> Hello,
>  
> Simple question, I have a control, its got focus, but
then the user 
> clics somewhere else (desktop lets say).
>  
> How do I catch a mouse event outside a window.

If you want all mouse events to be sent to your widget then
it can 
capture the mouse with... wait for it... the CaptureMouse()
method. 
After that has been done then all mouse events will be sent
to this 
widget until you call ReleaseMouse() or the system decides
that it needs 
to steal the capture from you for some reason.  (You'll get
a capture 
lost event in that case.)  Be sure to have a way to release
the mouse 
otherwise you can get stuck and not be able to do things
like close your 
own application.  In the demo there are a couple examples of
using 
CaptureMouse.

-- 
Robin Dunn
Software Craftsman
http://wxPython.org  Java
give you jitters?  Relax with wxPython!


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Robin Dunn wrote:
> Peter Damoc wrote:
>> Hi list,
>>
>> I'm playing a little bit with fonts recently and
I'm trying to 
>> understand what is pointSize.
>> I mean, I look at an image like this one:
>> http://en.wikipedia.org/wiki/Image:Typography_Line_T
erms.svg
>> and I ask myself. "What is pointSize?"  I
thought it should be 
>> Ascent+Descent?
> 
> Points is a typography metric that comes from the old
days of the hand 
> cranked printing press.  A point is 1/72 of an inch,
which means that if 
> you are setting type into a press that is 72 points
then the height of 
> the type glyphs you are putting in the press is about
one inch high.

Looks like there is a long history involved here: 
http://en.wik
ipedia.org/wiki/Point_size

-- 
Robin Dunn
Software Craftsman
http://wxPython.org  Java
give you jitters?  Relax with wxPython!


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Robin Dunn wrote:
> Peter Damoc wrote:
>> I'm trying to understand what is pointSize.
>> I mean, I look at an image like this one:
>> http://en.wikipedia.org/wiki/Image:Typography_Line_T
erms.svg
>> and I ask myself. "What is pointSize?"  I
thought it should be 
>> Ascent+Descent?

Robin answered the question of what is a pointSize vs. pixel
size, etc, 
but I think the OP had a slightly different question.

As far as I know, the "Point Size" (or pixel size,
for that matter) is a 
nominal dimension. As there are a lot of ways to measure a
font -- 
Ascender height, descender height, etc, and each character
in the font 
is different, and each font is different. I think you might
as well just 
think of it as a nominal size -- like a 2X4 is not 2"
by 4", and a 1" 
pipe is not 1", etc.

If I had to guess, I'd say that the "size" of a
font probably is about 
the cap height.

What's too bad is that wx does not provide a way to get
measurements 
to-from the baseline, or anything like that -- it's been
proposed, but I 
don't know if anyone is actually working on it.

-Chris




-- 
Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R            (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chris.Barkernoaa.gov

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Peter Damoc wrote:
> Some more details... I was trying to study for the
implementation of a 
> "drawn" toolkit. Basic controls. I started
with the buttons.
> I looked at the best, Apple HIG... I tried to use their
suggestions of 
> 13 points font... BUT the buttons looked huge.

I think you've hit one of my pet peeves -- systems that let
you specify 
font size in "points", where other stuff is in
pixels. The truth is that 
points make no sense in computers -- you need to know how
many dpi your 
display is -- but then, if you project on a  big screen, do
you want 
your fonts 13/72 of an inch tall? of course not!

In your case, if the font is huge, it's probably because the
system has 
the wrong dpi setting. Until we get fully scalable
everything (has Apple 
achieved that?), try to use a pixel size to set fonts if you
can.

> How would one draw consistent looking buttons, how
would one align the 
> text in these buttons.

That's a bit tough, as wx only gives you crude
DC.GetTextExtent -- and 
you can't draw text lined up at the baseline either.

Does GraphicsContext help this???

-Chris


-- 
Christopher Barker, Ph.D.
Oceanographer

Emergency Response Division
NOAA/NOS/OR&R            (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chris.Barkernoaa.gov

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