Description: Fix regression resolving bounding box of font glyphs

 Re-introduce over/underflow workaround

 .

 Commit 355434f4b1bbe8c4f98cafad5a6868aa2f0eaae1 reverted a workaround

 that compensated for over/underflow in Freetype's TTF hinting

 (related to freedom and projection vector calculations).

 That problem no longer exists in recent Freetype releases,

 and the workaround actually caused other issues to occur with hinting.

 .

 What wasn't obvious was

 that the workaround also protected over/underflow issues

 relating to the unitsPerEm value.

 .

 So this re-instates the workaround,

 but bases the decision on how the final scale is distributing

 between the Freetype "size" and the Freetype matrix

 on the unitsPerEm value

 (this is relevant for all font types

 as for non-TTF font types

 Freetype derives the unitsPerEm from the FontMatrix for PS type fonts).

Origin: upstream, http://git.ghostscript.com/?p=ghostpdl.git;h=06c9207

Author: Chris Liddell <chris.liddell@artifex.com>

Forwarded: yes

Bug: http://bugs.ghostscript.com/show_bug.cgi?id=700952

Bug: http://bugs.ghostscript.com/show_bug.cgi?id=700875

Bug-Debian: https://bugs.debian.org/927429

Last-Update: 2019-04-20

---

This patch header follows DEP-3: http://dep.debian.net/deps/dep3/

--- a/base/fapi_ft.c

+++ b/base/fapi_ft.c

@@ -974,13 +974,19 @@

  */

 static void

 transform_decompose(FT_Matrix * a_transform, FT_UInt * xresp, FT_UInt * yresp,

-                    FT_Fixed * a_x_scale, FT_Fixed * a_y_scale)

+                    FT_Fixed * a_x_scale, FT_Fixed * a_y_scale, int units_per_EM)

 {

     double scalex, scaley, fact = 1.0;

     double factx = 1.0, facty = 1.0;

     FT_Matrix ftscale_mat;

     FT_UInt xres;

     FT_UInt yres;

+    /* We have to account for units_per_EM as we fiddle with the scaling

+     * in order to avoid underflow (mostly in the TTF hinting code), but

+     * we also want to clamp to a lower value (512, admittedly arrived at

+     * via experimentation) in order to preserve the fidelity of the outlines.

+     */

+    double upe = units_per_EM > 512 ? (float)units_per_EM : 512.0;

     scalex = hypot((double)a_transform->xx, (double)a_transform->xy);

     scaley = hypot((double)a_transform->yx, (double)a_transform->yy);

@@ -1067,10 +1073,25 @@

         scalex *= fact;

     }

-    ftscale_mat.xx = (FT_Fixed) (65536.0 / scalex);

-    ftscale_mat.xy = (FT_Fixed) 0;

-    ftscale_mat.yx = (FT_Fixed) 0;

-    ftscale_mat.yy = (FT_Fixed) (65536.0 / scaley);

+    /* see above */

+    fact = 1.0;

+    while (scaley * yres > (double)upe * 72.0 && (xres > 0 && yres > 0)

+           && (scalex > 0.0 && scaley > 0.0)) {

+        if (scaley < yres) {

+            xres >>= 1;

+            yres >>= 1;

+            fact *= 2.0;

+        }

+        else {

+            scalex /= 1.25;

+            scaley /= 1.25;

+        }

+    }

+

+    ftscale_mat.xx = (FT_Fixed) ((65536.0 / scalex) * fact);

+    ftscale_mat.xy = 0;

+    ftscale_mat.yx = 0;

+    ftscale_mat.yy = (FT_Fixed) ((65536.0 / scaley) * fact);

     FT_Matrix_Multiply(a_transform, &ftscale_mat);

     memcpy(a_transform, &ftscale_mat, sizeof(FT_Matrix));

@@ -1315,7 +1336,7 @@

          * transform.

          */

         transform_decompose(&face->ft_transform, &face->horz_res,

-                            &face->vert_res, &face->width, &face->height);

+                            &face->vert_res, &face->width, &face->height, face->ft_face->units_per_EM);

         ft_error = FT_Set_Char_Size(face->ft_face, face->width, face->height,

                                     face->horz_res, face->vert_res);