[Bug 1001033] Re: Monospaced font is not monospaced

[Steve White]

Thanks, Sam!

(Sorry for being testy.)

Your problem of where to put the cursor is kind of messy for general
fonts (and I don't know the right answer -- probably one has to ask the
font rasterizer).  But for monospace fonts, there should be a
comprehensible solution at some higher level, such as your pygame thing.

Here's the arithmetic problem, as I see it.

For simplicity, say the advance widths of all characters are equal in
the font.  Suppose you scale the font, so the scaled width is some non-
integer multiple of the device pixel width.

Now you have made an API call to get the character width, and it returns
an integer.

What does that integer mean?  Maybe it's the non-integer multiple,
rounded.  Or maybe as I suggested it has something to do with which
pixels are turned on in the rendered graphic.  (And maybe there really
is a bug--I'm still not sure about this.)  In any case, the
documentation ought to explain it -- but I checked, and it doesn't.

Suggestion:

To place your cursor between letters.  Where should it go?  If you just get the width of a single character, and multiply by the character string index, the cursor is likely to be badly misplaced, due to rounding.
It might be better to find the pixel width of a longer string, and divide by the number of characters to get a floating-point value, and use that as the single-character width.  I the simple scenario, this should get you within a pixel of the expected position every time.

For completeness:

In general, the placement of the cursor in text is substantially more
subtle than that.  Even in a monospace font, it's permissible for a
character to have 0 width.  Furthermore, OpenType fonts can do various
tricks such as ligature substitution, that change the glyphs that are
actually rendered.  For this, the only safe way to place the cursor is
to ask the font rendering interface.  (This is just a deduction--I've
never done it myself.)

I don't know if Pygame has a representation of such an interface...

(And... let's please not talk about CPU cycles here.  It's just
embarrassing.)

Cheers!

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https://bugs.launchpad.net/bugs/1001033

Title:
  Monospaced font is not monospaced

Status in “freetype” package in Ubuntu:
  Confirmed

Bug description:
  The "FreeMono" font in Ubuntu 12.04 seems to not be monospaced.

  More information can be read at: http://www.mail-archive.com/pygame-
  users at seul.org/msg16829.html

  A little further testing after this discussion, and I've noticed I
  don't have the problem with the "Ubuntu Mono" font, it just seems to
  be the "FreeMono" font which is causing the problem.

  ProblemType: Bug
  DistroRelease: Ubuntu 12.04
  Package: apport-gtk 2.0.1-0ubuntu7
  ProcVersionSignature: Ubuntu 3.2.0-24.37-generic 3.2.14
  Uname: Linux 3.2.0-24-generic x86_64
  ApportLog:
   
  ApportVersion: 2.0.1-0ubuntu7
  Architecture: amd64
  CheckboxSubmission: d7186b4470c29fb9bde4930265e9b32c
  CheckboxSystem: 7e42599bda39ea7ff8b528272b6ef52b
  Date: Thu May 17 23:33:07 2012
  ExecutablePath: /usr/share/apport/apport-gtk
  InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
  InterpreterPath: /usr/bin/python2.7
  PackageArchitecture: all
  SourcePackage: apport
  UpgradeStatus: No upgrade log present (probably fresh install)

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