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bug#7887: Emacs will render some fonts under Mac OS X one pixel too tall

From: Jan D.
Subject: bug#7887: Emacs will render some fonts under Mac OS X one pixel too tall (patch supplied)
Date: Tue, 25 Jan 2011 14:03:02 +0100
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; sv-SE; rv: Gecko/20101207 Thunderbird/3.1.7

Anders Lindgren skrev 2011-01-22 10:43:

I have notices that Emacs will render some fonts under Mac OS X one
pixel too tall.

The current implementation for handling fonts under NextStep always
round the descender to the next full integer, to avoid clipping. (As
descenders under NextStep are negative, this is done using the
function "floor"). Unfortunately, some fonts do not specify the
descender as exactly as desired. Concretely, a 6x8 bitmap font could
report a descender of -2.0000040531158447 (represented by
0xc000000220000000), which Emacs rounds to -3. The result is that the
font will be drawn one pixel taller than expected.

The patch below is one example of how to handle this, it will
circumvent the problem by adding a small value to the descender,
making sure that values close enough to an integer will be rounded to
that integer.

How about checking if it is negative and then use ceil instead of floor, and keeping floor for the positive case?

        Jan D.

     -- Anders Lindgren

2011-01-22  Anders Lindgren<address@hidden>

        * nsfont.m (nsfont_open): Ensure that fonts with inexact
        descenders would not become one pixel too tall.

=== modified file 'src/nsfont.m'
--- src/nsfont.m        2011-01-19 22:11:33 +0000
+++ src/nsfont.m        2011-01-22 09:03:56 +0000
@@ -809,6 +809,15 @@
      const char *fontName = [[nsfont fontName] UTF8String];
      int len = strlen (fontName);

+    /* The values specified by fonts are not always exact. For
+     * example, a 6x8 font could specify that the descender is
+     * -2.00000405... (represented by 0xc000000220000000).  Without
+     * adjustment, the code below would round the descender to -3,
+     * resulting in a font that would be one pixel higher than
+     * intended. */
+    CGFloat adjusted_descender = [sfont descender] + 0.0001;
      font_info->nsfont = sfont;
@@ -830,7 +839,7 @@

      brect =  [sfont boundingRectForFont];
      full_height = brect.size.height;
-    min_height = [sfont ascender] - [sfont descender];
+    min_height = [sfont ascender] - adjusted_descender;
      hd = full_height - min_height;

      /* standard height, similar to Carbon. Emacs.app: was 0.5 by default. */
@@ -845,10 +854,10 @@
      /* max bounds */
      font_info->max_bounds.ascent =
        lrint (hshrink * [sfont ascender] + expand * hd/2);
-    /* [sfont descender] is usually negative.  Use floor to avoid
-       clipping descenders. */
+    /* Descender is usually negative.  Use floor to avoid clipping
+       descenders. */
      font_info->max_bounds.descent =
-      -lrint (floor(hshrink* [sfont descender] - expand*hd/2));
+      -lrint (floor(hshrink * adjusted_descender - expand * hd/2));
      font_info->height =
        font_info->max_bounds.ascent + font_info->max_bounds.descent;
      font_info->max_bounds.width = lrint (font_info->width);
@@ -884,7 +893,7 @@

      /* set up metrics portion of font struct */
      font->ascent = lrint([sfont ascender]);
-    font->descent = -lrint(floor([sfont descender]));
+    font->descent = -lrint(floor(adjusted_descender));
      font->min_width = ns_char_width(sfont, '|');
      font->space_width = lrint (ns_char_width (sfont, ' '));
      font->average_width = lrint (font_info->width);

In GNU Emacs (x86_64-apple-darwin10.5.0, NS apple-appkit-1038.35)
  of 2011-01-14 on macpro.local
Windowing system distributor `Apple', version 10.3.1038
configured using `configure  '--with-ns''

Important settings:
   value of $LC_ALL: nil
   value of $LC_COLLATE: nil
   value of $LC_CTYPE: nil
   value of $LC_MESSAGES: nil
   value of $LC_MONETARY: nil
   value of $LC_NUMERIC: nil
   value of $LC_TIME: nil
   value of $LANG: nil
   value of $XMODIFIERS: nil
   locale-coding-system: nil
   default enable-multibyte-characters: t

Major mode: ObjC/lw

Minor modes in effect:
   diff-auto-refine-mode: t
   subword-mode: t
   global-auto-revert-mode: t
   global-cwarn-mode: t
   minibuffer-electric-file-mode: t
   recentf-mode: t
   msb-mode: t
   display-time-mode: t
   tooltip-mode: t
   mouse-wheel-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   column-number-mode: t
   line-number-mode: t
   transient-mark-mode: t
   abbrev-mode: t

Recent input:
<down>  <down>  <down>  <down>  <down>  <down>  <down>  <down>
<down>  <down>  <down>  <down>  <down>  <down>  <down>  <down>
<down>  <down>  <down>  <down>  <down>  <down>  <down>  <down>
<down>  <down>  <down>  C-SPC<down>  C-w<down>  C-SPC
<down>  <down>  <down>  C-w<up>  C-e<left>  <left>  <left>
<M-backspace>  <backspace>  <backspace>  <backspace>  C-a
C-x C-s C-M-a C-s e p s C-a C-x C-f s a<backspace>
l a s j .<backspace>  <backspace>  k . c<return>  <C-tab>
C-x o<C-S-tab>  C-x p C-M-a<up>  <up>  <up>  <up>  <up>
<up>  <up>  <up>  <up>  C-SPC<down>  <down>  <down>  <down>
<down>  <down>  <down>  C-w C-x C-s C-x o C-y C-x p<down>
C-v C-l C-v<down>  <down-mouse-1>  <mouse-1>  C-a C-SPC
<down>  <down>  <down>  <down>  <down>  <down>  <down>  C-w
C-x C-s C-x o C-y C-x C-s C-x p<down-mouse-1>  <mouse-1>
M-d M-d M-d c o u l y<backspace>  d SPC<backspace>
M-f<backspace>  <backspace>  <backspace>  y<escape>
q<M-left>  <M-left>  <M-backspace>  <escape>  q<down>
<down>  M-f M-f M-f<M-backspace>  t h e SPC d e s c
M--<escape>  q C-x C-s<down-mouse-1>  <mouse-1>  <down-mouse-1>
<mouse-1>  <backspace>  C-a C-x C-s<down-mouse-1>  <mouse-1>
SPC<down-mouse-1>  <mouse-1>  SPC C-a C-x C-s<down-mouse-1>
<mouse-1>  SPC<down-mouse-1>  <mouse-1>  SPC C-a C-x
C-s<down-mouse-1>  <mouse-1>  C-a<down>  SPC<backspace>
<down>  <down>  <down>  <down>  <down>  <up>  SPC<backspace>
C-a C-x C-s<up>  <up>  <up>  <up>  M-f<right>  <right>
C-s C-w C-s C-a<down-mouse-1>  <mouse-1>  a<backspace>
a d j u s t m e n t<escape>  d<escape>  q<up>  <up>
<up>  C-a C-SPC<down>  <down>  <down>  <down>  <down>  <down>
<escape>  x i s p l l<backspace>  <backspace>  e l l
- r e g<tab>  '<backspace>  <return>  q<up>  C-g<up>
<down-mouse-1>  <mouse-1>  c<escape>  q<down-mouse-1>
<mouse-1>  C-d<backspace>  <backspace>  <backspace>  i
f y C-a C-x C-s<menu-bar>  <help-menu>  <send-emacs

Recent messages:
Wrote /Users/anders/build/emacs/trunk/src/nsfont.m
Mark saved where search started
Mark set
Starting new Ispell process [default] ...
Entering debugger...
Back to top level.
Saving file /Users/anders/build/emacs/trunk/src/nsfont.m...
Wrote /Users/anders/build/emacs/trunk/src/nsfont.m

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~/emacs/src/asm-mode-new/src/asm-mode hides

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