Get correct text metrics for distance fields, and fix dropouts due to thin features.

src/core/SkDistanceFieldGen.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDistanceFieldGen.h"
 #include "SkPoint.h"
 
@@ skipping 10 matching lines @@
     kTop_NeighborFlag         = 0x08,
     kTopRight_NeighborFlag    = 0x10,
     kBottomLeft_NeighborFlag  = 0x20,
     kBottom_NeighborFlag      = 0x40,
     kBottomRight_NeighborFlag = 0x80,
     kAll_NeighborFlags        = 0xff,
  
     kNeighborFlagCount        = 8
 };
 
-// We treat an "edge" as a place where we cross from a texel >= 128 to a texel < 128,
-// or vice versa. This means we just need to check if the MSBs are different.
+// We treat an "edge" as a place where we cross from black to non-black, or vice versa. 
 // 'neighborFlags' is used to limit the directions in which we test to avoid indexing
 // outside of the image
 static bool found_edge(const unsigned char* imagePtr, int width, int neighborFlags) {
     // the order of these should match the neighbor flags above
     const int kNum8ConnectedNeighbors = 8;
     const int offsets[8] = {-1, 1, -width-1, -width, -width+1, width-1, width, width+1 };
     SkASSERT(kNum8ConnectedNeighbors == kNeighborFlagCount);
 
     // search for an edge
-    unsigned char currVal = *imagePtr >> 7;
+    bool currVal = (*imagePtr != 0);
     for (int i = 0; i < kNum8ConnectedNeighbors; ++i) {
-        unsigned char checkVal;
+        bool checkVal;
         if ((1 << i) & neighborFlags) {
             const unsigned char* checkPtr = imagePtr + offsets[i];
-            checkVal = *checkPtr >> 7;
+            checkVal = (*checkPtr != 0);
         } else {
-            checkVal = 0;
+            checkVal = false;
         }
         SkASSERT(checkVal == 0 || checkVal == 1);
         SkASSERT(currVal == 0 || currVal == 1);
         if (checkVal != currVal) {
             return true;
         }
     }
 
     return false;
 }
@@ skipping 360 matching lines @@
         currEdge -= dataWidth-1;
     }
 
     // copy results to final distance field data
     currData = dataPtr + dataWidth+1;
     currEdge = edgePtr + dataWidth+1;
     unsigned char *dfPtr = distanceField;
     for (int j = 1; j < dataHeight-1; ++j) {
         for (int i = 1; i < dataWidth-1; ++i) {
 #if DUMP_EDGE
-            unsigned char val = (currData->fAlpha >= 0.5f) ? 255 : 0;
+            unsigned char val = sk_float_round2int(255*currData->fAlpha);
             if (*currEdge) {
                 val = 128;
             }
             *dfPtr++ = val;
 #else
             float dist;
             if (currData->fAlpha > 0.5f) {
                 dist = -SkScalarSqrt(currData->fDistSq);
             } else {
                 dist = SkScalarSqrt(currData->fDistSq);
             }
             *dfPtr++ = pack_distance_field_val(dist, (float)distanceMagnitude);
 #endif
             ++currData;
             ++currEdge;
         }
         currData += 2;
         currEdge += 2;
     }
 
     return true;
 }