Hook in rough distance field support for fonts

third_party/edtaa/edtaa3func.cpp

+/*
+ * edtaa3()
+ *
+ * Sweep-and-update Euclidean distance transform of an
+ * image. Positive pixels are treated as object pixels,
+ * zero or negative pixels are treated as background.
+ * An attempt is made to treat antialiased edges correctly.
+ * The input image must have pixels in the range [0,1],
+ * and the antialiased image should be a box-filter
+ * sampling of the ideal, crisp edge.
+ * If the antialias region is more than 1 pixel wide,
+ * the result from this transform will be inaccurate.
+ *
+ * By Stefan Gustavson (stefan.gustavson@gmail.com).
+ *
+ * Originally written in 1994, based on a verbal
+ * description of the SSED8 algorithm published in the
+ * PhD dissertation of Ingemar Ragnemalm. This is his
+ * algorithm, I only implemented it in C.
+ *
+ * Updated in 2004 to treat border pixels correctly,
+ * and cleaned up the code to improve readability.
+ *
+ * Updated in 2009 to handle anti-aliased edges.
+ *
+ * Updated in 2011 to avoid a corner case infinite loop.
+ *
+ * Updated 2012 to change license from LGPL to MIT.
+ */
+
+/*
+ Copyright (C) 2009-2012 Stefan Gustavson (stefan.gustavson@gmail.com)
+ The code in this file is distributed under the MIT license:
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy
+ of this software and associated documentation files (the "Software"), to deal
+ in the Software without restriction, including without limitation the rights
+ to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ copies of the Software, and to permit persons to whom the Software is
+ furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in
+ all copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ THE SOFTWARE.
+ */
+
+#include "edtaa3.h"
+
+#include <math.h>
+
+#if EDTAA_UNSIGNED_CHAR_INPUT
+#define IMG(i) ((double)(img[i] & 0xff)/256.0)
+#else
+#define IMG(i) (img[i])
+#endif
+
+namespace EDTAA {
+
+/*
+ * Compute the local gradient at edge pixels using convolution filters.
+ * The gradient is computed only at edge pixels. At other places in the
+ * image, it is never used, and it's mostly zero anyway.
+ */
+void computegradient(EdtaaImageType *img, int w, int h, double *gx, double *gy)
+{
+    int i,j,k;
+    double glength;
+#define SQRT2 1.4142136
+    for(i = 1; i < h-1; i++) { // Avoid edges where the kernels would spill over
+        for(j = 1; j < w-1; j++) {
+            k = i*w + j;
+            if((IMG(k)>0.0) && (IMG(k)<1.0)) { // Compute gradient for edge pixels only
+                gx[k] = -IMG(k-w-1) - SQRT2*IMG(k-1) - IMG(k+w-1) + IMG(k-w+1) + SQRT2*IMG(k+1) + IMG(k+w+1);
+                gy[k] = -IMG(k-w-1) - SQRT2*IMG(k-w) - IMG(k+w-1) + IMG(k-w+1) + SQRT2*IMG(k+w) + IMG(k+w+1);
+                glength = gx[k]*gx[k] + gy[k]*gy[k];
+                if(glength > 0.0) { // Avoid division by zero
+                    glength = sqrt(glength);
+                    gx[k]=gx[k]/glength;
+                    gy[k]=gy[k]/glength;
+                }
+            }
+        }
+    }
+    // TODO: Compute reasonable values for gx, gy also around the image edges.
+    // (These are zero now, which reduces the accuracy for a 1-pixel wide region
+        // around the image edge.) 2x2 kernels would be suitable for this.
+}
+
+/*
+ * A somewhat tricky function to approximate the distance to an edge in a
+ * certain pixel, with consideration to either the local gradient (gx,gy)
+ * or the direction to the pixel (dx,dy) and the pixel greyscale value a.
+ * The latter alternative, using (dx,dy), is the metric used by edtaa2().
+ * Using a local estimate of the edge gradient (gx,gy) yields much better
+ * accuracy at and near edges, and reduces the error even at distant pixels
+ * provided that the gradient direction is accurately estimated.
+ */
+static double edgedf(double gx, double gy, double a)
+{
+    double df, glength, temp, a1;
+
+    if ((gx == 0) || (gy == 0)) { // Either A) gu or gv are zero, or B) both
+        df = 0.5-a;  // Linear approximation is A) correct or B) a fair guess
+    } else {
+        glength = sqrt(gx*gx + gy*gy);
+        if(glength>0) {
+            gx = gx/glength;
+            gy = gy/glength;
+        }
+        /* Everything is symmetric wrt sign and transposition,
+         * so move to first octant (gx>=0, gy>=0, gx>=gy) to
+         * avoid handling all possible edge directions.
+         */
+        gx = fabs(gx);
+        gy = fabs(gy);
+        if(gx<gy) {
+            temp = gx;
+            gx = gy;
+            gy = temp;
+        }
+        a1 = 0.5*gy/gx;
+        if (a < a1) { // 0 <= a < a1
+            df = 0.5*(gx + gy) - sqrt(2.0*gx*gy*a);
+        } else if (a < (1.0-a1)) { // a1 <= a <= 1-a1
+            df = (0.5-a)*gx;
+        } else { // 1-a1 < a <= 1
+            df = -0.5*(gx + gy) + sqrt(2.0*gx*gy*(1.0-a));
+        }
+    }    
+    return df;
+}
+
+static double distaa3(EdtaaImageType *img, double *gximg, double *gyimg, int w, int c, int xc, int yc, int xi, int yi)
+{
+  double di, df, dx, dy, gx, gy, a;
+  int closest;
+  
+  closest = c-xc-yc*w; // Index to the edge pixel pointed to from c
+  a = IMG(closest);    // Grayscale value at the edge pixel
+  gx = gximg[closest]; // X gradient component at the edge pixel
+  gy = gyimg[closest]; // Y gradient component at the edge pixel
+  
+  if(a > 1.0) a = 1.0;
+  if(a < 0.0) a = 0.0; // Clip grayscale values outside the range [0,1]
+  if(a == 0.0) return 1000000.0; // Not an object pixel, return "very far" ("don't know yet")
+
+  dx = (double)xi;
+  dy = (double)yi;
+  di = sqrt(dx*dx + dy*dy); // Length of integer vector, like a traditional EDT
+  if(di==0) { // Use local gradient only at edges
+      // Estimate based on local gradient only
+      df = edgedf(gx, gy, a);
+  } else {
+      // Estimate gradient based on direction to edge (accurate for large di)
+      df = edgedf(dx, dy, a);
+  }
+  return di + df; // Same metric as edtaa2, except at edges (where di=0)
+}
+
+// Shorthand macro: add ubiquitous parameters dist, gx, gy, img and w and call distaa3()
+#define DISTAA(c,xc,yc,xi,yi) (distaa3(img, gx, gy, w, c, xc, yc, xi, yi))
+
+void edtaa3(EdtaaImageType *img, double *gx, double *gy, int w, int h, short *distx, short *disty, double *dist)
+{
+  int x, y, i, c;
+  int offset_u, offset_ur, offset_r, offset_rd,
+  offset_d, offset_dl, offset_l, offset_lu;
+  double olddist, newdist;
+  int cdistx, cdisty, newdistx, newdisty;
+  int changed;
+  double epsilon = 1e-3;
+  double a;
+
+  /* Initialize index offsets for the current image width */
+  offset_u = -w;
+  offset_ur = -w+1;
+  offset_r = 1;
+  offset_rd = w+1;
+  offset_d = w;
+  offset_dl = w-1;
+  offset_l = -1;
+  offset_lu = -w-1;
+
+  /* Initialize the distance images */
+  for(i=0; i<w*h; i++) {
+    distx[i] = 0; // At first, all pixels point to
+    disty[i] = 0; // themselves as the closest known.
+    a = IMG(i);
+    if(a <= 0.0)
+      {
+        dist[i]= 1000000.0; // Big value, means "not set yet"
+      }
+    else if (a<1.0) {
+      dist[i] = edgedf(gx[i], gy[i], a); // Gradient-assisted estimate
+    }
+    else {
+      dist[i]= 0.0; // Inside the object
+    }
+  }
+
+  /* Perform the transformation */
+  do
+    {
+      changed = 0;
+
+      /* Scan rows, except first row */
+      for(y=1; y<h; y++)
+        {
+
+          /* move index to leftmost pixel of current row */
+          i = y*w;
+
+          /* scan right, propagate distances from above & left */
+
+          /* Leftmost pixel is special, has no left neighbors */
+          olddist = dist[i];
+          if(olddist > 0) // If non-zero distance or not set yet
+            {
+              c = i + offset_u; // Index of candidate for testing
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx;
+              newdisty = cdisty+1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_ur;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx-1;
+              newdisty = cdisty+1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+          i++;
+
+          /* Middle pixels have all neighbors */
+          for(x=1; x<w-1; x++, i++)
+            {
+              olddist = dist[i];
+              if(olddist <= 0) continue; // No need to update further
+
+              c = i+offset_l;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx+1;
+              newdisty = cdisty;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_lu;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx+1;
+              newdisty = cdisty+1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_u;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx;
+              newdisty = cdisty+1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_ur;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx-1;
+              newdisty = cdisty+1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+
+          /* Rightmost pixel of row is special, has no right neighbors */
+          olddist = dist[i];
+          if(olddist > 0) // If not already zero distance
+            {
+              c = i+offset_l;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx+1;
+              newdisty = cdisty;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_lu;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx+1;
+              newdisty = cdisty+1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_u;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx;
+              newdisty = cdisty+1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+
+          /* Move index to second rightmost pixel of current row. */
+          /* Rightmost pixel is skipped, it has no right neighbor. */
+          i = y*w + w-2;
+
+          /* scan left, propagate distance from right */
+          for(x=w-2; x>=0; x--, i--)
+            {
+              olddist = dist[i];
+              if(olddist <= 0) continue; // Already zero distance
+
+              c = i+offset_r;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx-1;
+              newdisty = cdisty;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+        }
+      
+      /* Scan rows in reverse order, except last row */
+      for(y=h-2; y>=0; y--)
+        {
+          /* move index to rightmost pixel of current row */
+          i = y*w + w-1;
+
+          /* Scan left, propagate distances from below & right */
+
+          /* Rightmost pixel is special, has no right neighbors */
+          olddist = dist[i];
+          if(olddist > 0) // If not already zero distance
+            {
+              c = i+offset_d;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx;
+              newdisty = cdisty-1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_dl;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx+1;
+              newdisty = cdisty-1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+          i--;
+
+          /* Middle pixels have all neighbors */
+          for(x=w-2; x>0; x--, i--)
+            {
+              olddist = dist[i];
+              if(olddist <= 0) continue; // Already zero distance
+
+              c = i+offset_r;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx-1;
+              newdisty = cdisty;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_rd;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx-1;
+              newdisty = cdisty-1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_d;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx;
+              newdisty = cdisty-1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_dl;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx+1;
+              newdisty = cdisty-1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+          /* Leftmost pixel is special, has no left neighbors */
+          olddist = dist[i];
+          if(olddist > 0) // If not already zero distance
+            {
+              c = i+offset_r;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx-1;
+              newdisty = cdisty;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_rd;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx-1;
+              newdisty = cdisty-1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  olddist=newdist;
+                  changed = 1;
+                }
+
+              c = i+offset_d;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx;
+              newdisty = cdisty-1;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+
+          /* Move index to second leftmost pixel of current row. */
+          /* Leftmost pixel is skipped, it has no left neighbor. */
+          i = y*w + 1;
+          for(x=1; x<w; x++, i++)
+            {
+              /* scan right, propagate distance from left */
+              olddist = dist[i];
+              if(olddist <= 0) continue; // Already zero distance
+
+              c = i+offset_l;
+              cdistx = distx[c];
+              cdisty = disty[c];
+              newdistx = cdistx+1;
+              newdisty = cdisty;
+              newdist = DISTAA(c, cdistx, cdisty, newdistx, newdisty);
+              if(newdist < olddist-epsilon)
+                {
+                  distx[i]=newdistx;
+                  disty[i]=newdisty;
+                  dist[i]=newdist;
+                  changed = 1;
+                }
+            }
+        }
+    }
+  while(changed); // Sweep until no more updates are made
+
+  /* The transformation is completed. */
+
+}
+
+} // namespace EDTAA