More distance field improvements

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 black to non-black, or vice versa.
+// We treat an "edge" as a place where we cross from >=128 to <128, or vice versa, or
+// where we have two non-zero pixels that are <128.
 // '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
-    bool currVal = (*imagePtr != 0);
+    unsigned char currVal = *imagePtr;
+    unsigned char currCheck = (currVal >> 7);
     for (int i = 0; i < kNum8ConnectedNeighbors; ++i) {
-        bool checkVal;
+        unsigned char neighborVal;
         if ((1 << i) & neighborFlags) {
             const unsigned char* checkPtr = imagePtr + offsets[i];
-            checkVal = (*checkPtr != 0);
+            neighborVal = *checkPtr;
         } else {
-            checkVal = false;
+            neighborVal = 0;
         }
-        SkASSERT(checkVal == 0 || checkVal == 1);
-        SkASSERT(currVal == 0 || currVal == 1);
-        if (checkVal != currVal) {
+        unsigned char neighborCheck = (neighborVal >> 7);
+        SkASSERT(currCheck == 0 || currCheck == 1);
+        SkASSERT(neighborCheck == 0 || neighborCheck == 1);
+        // if sharp transition
+        if (currCheck != neighborCheck ||
+            // or both <128 and >0
+            (!currCheck && !neighborCheck && currVal && neighborVal)) {
             return true;
         }
     }
 
     return false;
 }
 
 static void init_glyph_data(DFData* data, unsigned char* edges, const unsigned char* image,
                             int dataWidth, int dataHeight,
                             int imageWidth, int imageHeight,
@@ skipping 279 matching lines @@
     // create temp data
     size_t dataSize = dataWidth*dataHeight*sizeof(DFData);
     SkAutoSMalloc<1024> dfStorage(dataSize);
     DFData* dataPtr = (DFData*) dfStorage.get();
     sk_bzero(dataPtr, dataSize);
 
     SkAutoSMalloc<1024> edgeStorage(dataWidth*dataHeight*sizeof(char));
     unsigned char* edgePtr = (unsigned char*) edgeStorage.get();
     sk_bzero(edgePtr, dataWidth*dataHeight*sizeof(char));
 
+    SkAutoSMalloc<1024> copyStorage((width+2)*(height+2)*sizeof(char));
+    unsigned char* copyPtr = (unsigned char*) copyStorage.get();
+
+    // we copy our source image into a padded copy to ensure we catch edge transitions
+    // around the outside
+    const unsigned char* currImage = image;
+    sk_bzero(copyPtr, (width+2)*sizeof(char));
+    unsigned char* currCopy = copyPtr + width + 2;
+    for (int i = 0; i < height; ++i) {
+        *currCopy++ = 0; 
+        memcpy(currCopy, currImage, width*sizeof(char));
+        currImage += width;
+        currCopy += width;
+        *currCopy++ = 0;
+    }
+    sk_bzero(currCopy, (width+2)*sizeof(char));
+
     // copy glyph into distance field storage
-    init_glyph_data(dataPtr, edgePtr, image,
+    init_glyph_data(dataPtr, edgePtr, copyPtr,
                     dataWidth, dataHeight,
-                    width, height, pad);
+                    width+2, height+2, pad-1);
 
     // create initial distance data, particularly at edges
     init_distances(dataPtr, edgePtr, dataWidth, dataHeight);
 
     // now perform Euclidean distance transform to propagate distances
 
     // forwards in y
     DFData* currData = dataPtr+dataWidth+1; // skip outer buffer
     unsigned char* currEdge = edgePtr+dataWidth+1;
     for (int j = 1; j < dataHeight-1; ++j) {
@@ skipping 53 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 = sk_float_round2int(255*currData->fAlpha);
+            float alpha = currData->fAlpha;
+            float edge = 0.0f;
             if (*currEdge) {
-                val = 128;
+                edge = 0.25f;
             }
+            // blend with original image
+            float result = alpha + (1.0f-alpha)*edge;
+            unsigned char val = sk_float_round2int(255*result);
             *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;
 }