Linux: calculate fractional xheight

We need to push the calculation of the x-height into Skia. For one of
the layout tests, it assumes that 2.5ex of Ahem is exactly 32px.
Previously we calculated the x-height of Ahem to be 13px, so 2.5*13 was
33px.

Now we use the 26.6 fixed point number from freetype's hinter and turn
that directly into a floating point value (x-height is the only WebKit
metric which is a floating point value).

This lets us pass LayoutTests/css2.1/t1507-c526-font-sz-02-b-a.html
(although the Windows baseline is wrong)

Review URL: http://codereview.chromium.org/13112


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@6344 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 14 insertions, 0 deletions

diff --git a/skia/include/SkPaint.h b/skia/include/SkPaint.h
index 9529dd0..cc6f760 100644
--- a/skia/include/SkPaint.h
+++ b/skia/include/SkPaint.h
@@ -592,6 +592,7 @@ public:
                                     //   in units of em. It's used to calculate a value which
                                     //   matches Windows's GetTextMetrics tmMaxCharWidth
                                     //   member exactly.
+        SkScalar    fXHeight;   //!< the height of an 'x' in px, or 0 if no 'x' in face
 
         // VDMX values are exact ascent and descent values for scalable fonts at
         // a certain pixel size.
diff --git a/skia/ports/SkFontHost_FreeType.cpp b/skia/ports/SkFontHost_FreeType.cpp
index 46c86b6..ac938ec 100644
--- a/skia/ports/SkFontHost_FreeType.cpp
+++ b/skia/ports/SkFontHost_FreeType.cpp
@@ -810,6 +810,17 @@ void SkScalerContext_FreeType::generateFontMetrics(SkPaint::FontMetrics* mx, SkP
     ys[5] = face->height;
     ys[6] = os2 ? os2->xAvgCharWidth : 0;
 
+    SkScalar x_height;
+    const FT_UInt x_glyph = FT_Get_Char_Index(fFace, 'x');
+    if (x_glyph) {
+        FT_BBox bbox;
+        FT_Load_Glyph(fFace, x_glyph, fLoadGlyphFlags);
+        FT_Outline_Get_CBox(&fFace->glyph->outline, &bbox);
+        x_height = static_cast<SkScalar>(bbox.yMax) / 64;
+    } else {
+        x_height = 0;
+    }
+
     // convert upem-y values into scalar points
     for (int i = 0; i < 7; i++)
     {
@@ -829,6 +840,7 @@ void SkScalerContext_FreeType::generateFontMetrics(SkPaint::FontMetrics* mx, SkP
         mx->fHeight = pts[5].fX;
         mx->fAvgCharWidth = pts[6].fX;
         mx->fXRange = xrange;
+        mx->fXHeight = x_height;
 
         // The VDMX metrics only make sense in the horizontal direction
         // I believe
@@ -844,6 +856,7 @@ void SkScalerContext_FreeType::generateFontMetrics(SkPaint::FontMetrics* mx, SkP
         my->fHeight = pts[5].fY;
         my->fAvgCharWidth = pts[6].fY;
         my->fXRange = xrange;
+        my->fXHeight = x_height;
         my->fVDMXMetricsValid = false;
 
         // Attempt to parse the VDMX table to get exact metrics