Glyph positions maintain 32 bit integer part.

src/core/SkTextMapStateProc.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTextMapStateProc_DEFINED
 #define SkTextMapStateProc_DEFINED
 
@@ skipping 37 matching lines @@
         kXY,
         kOnlyScaleX,
         kOnlyTransX,
         kX
     } fMapCase;
     const SkMatrix::MapXYProc fProc;
     SkPoint  fOffset; // In kOnly* mode, this includes the matrix translation component.
     SkScalar fScaleX; // This is only used by kOnly... cases.
 };
 
+static inline SkScalar SkClampScalarToFixed(SkScalar a) {
+    return SkScalarPin(a, SkIntToScalar(-16384), SkIntToScalar(16384));

[mtklein, 2015/03/04 21:45:30]

What fixed format are we clamping to?  Signed 1.14?  2.14?  Not SkFixed, right?

Doesn't the max need to be 16383 if the min is -16384?

[bungeman-skia, 2015/03/04 21:57:35]

This is SkFixed we're clamping to. SkFixed is symmetrical with the 'most
negative' value being the NaN. Anyhow, there's a sign bit and then 15 bits for
the whole part and then 16 for the fractional part. So the range of SkFixed is
actually +-2^15, but this clamps to +-2^14. Te reason for the slop is just to
avoid glyphs being nudged over by subpixel and the like, as well as to ensure
the entire bounds of the glyph stays inside device space (but outside any
view-able space).

[mtklein, 2015/03/04 22:11:00]

Oh, duh, we're clamping SkScalars, not SkFixed.  OK, unconfused now I think.

But why do we want to clamp to [min/2, max/2] instead of [min,max] ?

[reed1, 2015/03/05 18:27:35]

Lets modify its name to make it more obvious that its not clamping to fixed's
range. clamp-to-half-fixed-range?

+}
+
 inline void SkTextMapStateProc::operator()(const SkScalar pos[], SkPoint* loc) const {
     switch(fMapCase) {
     case kXY:
         fProc(fMatrix, pos[0] + fOffset.x(), pos[1] + fOffset.y(), loc);
         break;
     case kOnlyScaleX:
         loc->set(SkScalarMul(fScaleX, *pos) + fOffset.x(), fOffset.y());
         break;
     case kOnlyTransX:
         loc->set(*pos + fOffset.x(), fOffset.y());
         break;
     default:
         SkASSERT(false);
     case kX:
         fProc(fMatrix, *pos + fOffset.x(), fOffset.y(), loc);
         break;
     }
+    loc->set(SkClampScalarToFixed(loc->x()), SkClampScalarToFixed(loc->y()));
 }
 
 #endif