Re: [ft-devel] Autohinter only works for unrotated text

[James Cloos]

>>>>> "Graham" == Graham Asher <address@hidden> writes:

Graham> When I coded this up for a private project a while ago I took a
Graham> simpler approach: I used the matrix to convert the point (1,0) to a
Graham> new point. If the new point is (x,0), (0,x), (-x,0) or (0,-x) for any
Graham> x we have a rotation by a multiple of 90 degrees, neglecting any
Graham> slant; the slant is ignored because we are transforming a vector along
Graham> the baseline, and that's what we're interested in.

Applying the matrix to the point (1,0) is a great idea.  The result is
Sx×cos(θ), −Sx×sin(θ) or, picking from the matrix itself, (xx,yx).

The check, then, is:

  (xx == 0 && yx != 0) || (yx == 0 && xx != 0)

Graham> This system worked perfectly.

Again, great simplification!

A proposed changeset is:

>From 5b1e0c0f4cc29a278cc2169c04dc56907a220f32 Mon Sep 17 00:00:00 2001
From: James Cloos <address@hidden>
Date: Wed, 27 May 2009 17:16:38 -0400
Subject: [PATCH 1/1] 
=?utf-8?q?Allow=20autohinting=20when=20rotating=20by=20multiples=20of=2090=C2=B0.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit

* src/base/ftobjs.c (FT_Load_Glyph): alter check for permitted
matrices to allow rotations by multiples of 90°, not only un-
rotated, possibility slanted matrices.

Signed-off-by: James Cloos <address@hidden>
---
 src/base/ftobjs.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/base/ftobjs.c b/src/base/ftobjs.c
index 613deef..c1ce2fd 100644
--- a/src/base/ftobjs.c
+++ b/src/base/ftobjs.c
@@ -590,7 +590,8 @@
      *
      * - Do only auto-hinting if we have a hinter module,
      *   a scalable font format dealing with outlines,
-     *   and no transforms except simple slants.
+     *   and no transforms except simple slants and/or
+     *   rotations by integer multiples of 90 degrees.
      *
      * - Then, autohint if FT_LOAD_FORCE_AUTOHINT is set
      *   or if we don't have a native font hinter.
@@ -607,8 +608,10 @@
          FT_DRIVER_IS_SCALABLE( driver )          &&
          FT_DRIVER_USES_OUTLINES( driver )        &&
          !FT_IS_TRICKY( face )                    &&
-         face->internal->transform_matrix.yy > 0  &&
-         face->internal->transform_matrix.yx == 0 )
+         ( ( face->internal->transform_matrix.yx == 0 &&
+             face->internal->transform_matrix.xx != 0 ) ||
+           ( face->internal->transform_matrix.xx == 0 &&
+             face->internal->transform_matrix.yx != 0 ) ) )
     {
       if ( ( load_flags & FT_LOAD_FORCE_AUTOHINT ) ||
            !FT_DRIVER_HAS_HINTER( driver )         )
-- 
1.6.3.rc0.53.g1a1f0.dirty


-JimC
-- 
James Cloos <address@hidden>         OpenPGP: 1024D/ED7DAEA6