From 3386e586ac0f0ae07535036efe6293f6118f7e2b Mon Sep 17 00:00:00 2001
From: jaseg <git@jaseg.de>
Date: Tue, 1 Jun 2021 23:36:32 +0200
Subject: Work on chain approx

---
 svg-flatten/src/nopencv.cpp | 222 ++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 203 insertions(+), 19 deletions(-)

(limited to 'svg-flatten/src/nopencv.cpp')

diff --git a/svg-flatten/src/nopencv.cpp b/svg-flatten/src/nopencv.cpp
index 22c3fff..f42b6ad 100644
--- a/svg-flatten/src/nopencv.cpp
+++ b/svg-flatten/src/nopencv.cpp
@@ -1,5 +1,6 @@
 
 #include <iostream>
+#include <iomanip>
 
 #include "nopencv.hpp"
 
@@ -37,17 +38,17 @@ static struct {
 } dir_to_coords[8] = {{0, -1}, {1, -1}, {1, 0}, {1, 1}, {0, 1}, {-1, 1}, {-1, 0}, {-1, -1}};
 
 static Direction flip_direction[8] = {
-    D_S,
-    D_SW,
-    D_W,
-    D_NW,
-    D_N,
-    D_NE,
-    D_E,
-    D_SE
+    D_S,  /* 0 */
+    D_SW, /* 1 */
+    D_W,  /* 2 */
+    D_NW, /* 3 */
+    D_N,  /* 4 */
+    D_NE, /* 5 */
+    D_E,  /* 6 */
+    D_SE  /* 7 */
 };
 
-static void follow(gerbolyze::nopencv::Image32 &img, int start_x, int start_y, Direction initial_direction, int nbd, int connectivity, Polygon &poly) {
+static void follow(gerbolyze::nopencv::Image32 &img, int start_x, int start_y, Direction initial_direction, int nbd, int connectivity, Polygon_i &poly) {
 
     //cerr << "follow " << start_x << " " << start_y << " | dir=" << dir_str[initial_direction] << " nbd=" << nbd << " conn=" << connectivity << endl;
     int dir_inc = (connectivity == 4) ? 2 : 1;
@@ -69,10 +70,11 @@ static void follow(gerbolyze::nopencv::Image32 &img, int start_x, int start_y, D
 
     if (!found) { /* No nonzero pixels found. This is a single-pixel contour */
         img.at(start_x, start_y) = nbd;
-        poly.emplace_back(d2p{(double)start_x,   (double)start_y});
-        poly.emplace_back(d2p{(double)start_x+1, (double)start_y});
-        poly.emplace_back(d2p{(double)start_x+1, (double)start_y+1});
-        poly.emplace_back(d2p{(double)start_x,   (double)start_y+1});
+        poly.emplace_back(i2p{start_x,   start_y});
+        poly.emplace_back(i2p{start_x+1, start_y});
+        poly.emplace_back(i2p{start_x+1, start_y+1});
+        poly.emplace_back(i2p{start_x,   start_y+1});
+
         return;
     }
 
@@ -106,10 +108,10 @@ static void follow(gerbolyze::nopencv::Image32 &img, int start_x, int start_y, D
 
         for (int l = (current_direction + 8 - 2 + 1) / 2 * 2; l > k; l -= dir_inc) {
             switch (l%8) {
-                case 0: poly.emplace_back(d2p{(double)center_x,   (double)center_y}); break;
-                case 2: poly.emplace_back(d2p{(double)center_x+1, (double)center_y}); break;
-                case 4: poly.emplace_back(d2p{(double)center_x+1, (double)center_y+1}); break;
-                case 6: poly.emplace_back(d2p{(double)center_x,   (double)center_y+1}); break;
+                case 0: poly.emplace_back(i2p{center_x,   center_y}); break;
+                case 2: poly.emplace_back(i2p{center_x+1, center_y}); break;
+                case 4: poly.emplace_back(i2p{center_x+1, center_y+1}); break;
+                case 6: poly.emplace_back(i2p{center_x,   center_y+1}); break;
             }
         }
 
@@ -123,8 +125,15 @@ static void follow(gerbolyze::nopencv::Image32 &img, int start_x, int start_y, D
 
 
 void gerbolyze::nopencv::find_blobs(gerbolyze::nopencv::Image32 &img, gerbolyze::nopencv::ContourCallback cb) {
+    /* Implementation of the hierarchical contour finding algorithm from Suzuki and Abe, 1983: Topological Structural
+     * Analysis of Digitized Binary Images by Border Following
+     *
+     * Written with these two resources as reference:
+     *     https://theailearner.com/tag/suzuki-contour-algorithm-opencv/
+     *     https://github.com/FreshJesh5/Suzuki-Algorithm/blob/master/contoursv1/contoursv1.cpp
+     */
     int nbd = 1;
-    Polygon poly;
+    Polygon_i poly;
     for (int y=0; y<img.rows(); y++) {
         for (int x=0; x<img.cols(); x++) {
             int val_xy = img.at(x, y);
@@ -147,7 +156,7 @@ void gerbolyze::nopencv::find_blobs(gerbolyze::nopencv::Image32 &img, gerbolyze:
 
             } else if (val_xy >= 1 && img.at_default(x+1, y) == 0) { /* hole border starting point */
                 nbd += 1;
-                follow(img, x, y, D_E, nbd, 4, poly);
+                follow(img, x, y, D_E, nbd, 8, poly);
                 cb(poly, CP_HOLE);
                 poly.clear();
             }
@@ -155,3 +164,178 @@ void gerbolyze::nopencv::find_blobs(gerbolyze::nopencv::Image32 &img, gerbolyze:
     }
 }
 
+static size_t region_of_support(Polygon_i poly, size_t i) { 
+    double x0 = poly[i][0], y0 = poly[i][1];
+    size_t sz = poly.size();
+    double last_l = 0;
+    double last_r = 0;
+    size_t k;
+    for (k=0; k<sz/2; k++) {
+        size_t idx1 = (i + k) % sz;
+        size_t idx2 = (i + sz - k) % sz;
+        double x1 = poly[idx1][0], y1 = poly[idx1][1], x2 = poly[idx2][0], y2 = poly[idx2][1];
+        double l = sqrt(pow(x2-x1, 2) + pow(y2-y1, 2));
+        /* https://en.wikipedia.org/wiki/Distance_from_a_point_to_a_line
+         * TODO: Check whether distance-to-line is an ok implementation here, the paper asks for distance to chord.
+         */
+        double d = ((x2-x1)*(y1-y0) - (x1-x0)*(y2-y1)) / sqrt(pow(x2-x1, 2) + pow(y2-y1, 2));
+        double r = d/l;
+
+        bool cond_a = l < last_l;
+        bool cond_b = (d > 0) ? (r < last_r) : (r > last_r);
+
+        if (cond_a || cond_b)
+            break;
+
+        last_l = l;
+        last_r = r;
+    }
+    k -= 1;
+    return k;
+}
+
+int freeman_angle(const Polygon_i &poly, size_t i) {
+    /* f:
+     *        2
+     *   3         1
+     *        ^   
+     *        |
+     * 4 <--- X ---> 0
+     *        |
+     *        v
+     *   5         7
+     *        6
+     *
+     */
+    size_t sz = poly.size();
+
+    auto &p_last = poly[(i + sz - 1) % sz];
+    auto &p_now = poly[i];
+    auto dx = p_now[0] - p_last[0];
+    auto dy = p_now[1] - p_last[1];
+    /* both points must be neighbors */
+    assert (-1 <= dx && dx <= 1);
+    assert (-1 <= dy && dy <= 1);
+    assert (!(dx == 0 && dy == 0));
+
+    int lut[3][3] = {{3, 2, 1}, {4, -1, 0}, {5, 6, 7}};
+    return lut[dy+1][dx+1];
+}
+
+double k_curvature(const Polygon_i &poly, size_t i, size_t k) {
+    size_t sz = poly.size();
+    double acc = 0;
+    for (size_t idx = 0; idx < k; idx++) {
+        acc += freeman_angle(poly, (i + 2*sz - idx) % sz) - freeman_angle(poly, (i+idx + 1) % sz);
+    }
+    return acc / (2*k);
+}
+
+double k_cos(const Polygon_i &poly, size_t i, size_t k) {
+    size_t sz = poly.size();
+    int64_t x0 = poly[i][0], y0 = poly[i][1];
+    int64_t x1 = poly[(i + sz + k) % sz][0], y1 = poly[(i + sz + k) % sz][1];
+    int64_t x2 = poly[(i + sz - k) % sz][0], y2 = poly[(i + sz - k) % sz][1];
+    auto xa = x0 - x1, ya = y0 - y1;
+    auto xb = x0 - x2, yb = y0 - y2;
+    auto dp = xa*yb + ya*xb;
+    auto sq_a = xa*xa + ya*ya;
+    auto sq_b = xb*xb + yb*yb;
+    return dp / (sqrt(sq_a)*sqrt(sq_b));
+}
+
+ContourCallback gerbolyze::nopencv::simplify_contours_teh_chin(int kcos, ContourCallback cb) {
+    return [&cb, kcos](Polygon_i &poly, ContourPolarity cpol) {
+        size_t sz = poly.size();
+        vector<size_t> ros(sz);
+        vector<double> sig(sz);
+        vector<bool> retain(sz);
+        for (size_t i=0; i<sz; i++) {
+            ros[i] = region_of_support(poly, i);
+            sig[i] = fabs(k_cos(poly, i, kcos));
+            retain[i] = true;
+        }
+
+        cerr << endl;
+        cerr << "Polarity: " << cpol <<endl;
+        cerr << "Coords:"<<endl;
+        cerr << "  x: ";
+        for (size_t i=0; i<sz; i++) {
+            cerr << setfill(' ') << setw(2) << poly[i][0] << " ";
+        }
+        cerr << endl;
+        cerr << "  y: ";
+        for (size_t i=0; i<sz; i++) {
+            cerr << setfill(' ') << setw(2) << poly[i][1] << " ";
+        }
+        cerr << endl;
+        cerr << "Metrics:"<<endl;
+        cerr << "ros: ";
+        for (size_t i=0; i<sz; i++) {
+            cerr << setfill(' ') << setw(2) << ros[i] << " ";
+        }
+        cerr << endl;
+        cerr << "sig: ";
+        for (size_t i=0; i<sz; i++) {
+            cerr << setfill(' ') << setw(2) << sig[i] << " ";
+        }
+        cerr << endl;
+
+        /* 3a, Pass 1: Non-maxima suppression */
+        for (size_t i=0; i<sz; i++) {
+            for (size_t j=0; j<ros[i]/2; j++) {
+                if (sig[i] < sig[(i + j) % sz] || sig[i] < sig[(i + sz - j) % sz]) {
+                    retain[i] = false;
+                    break;
+                }
+            }
+        }
+
+        cerr << "pass 1: ";
+        for (size_t i=0; i<sz; i++) {
+            cerr << (retain[i] ? "#" : ".");
+        }
+        cerr << endl;
+        
+        /* 3b, Pass 2: Zero-curvature suppression */
+        for (size_t i=0; i<sz; i++) {
+            if (retain[i] && k_cos(poly, i, kcos) == 0) {
+                retain[i] = false;
+            }
+        }
+
+        cerr << "pass 2: ";
+        for (size_t i=0; i<sz; i++) {
+            cerr << (retain[i] ? "#" : ".");
+        }
+        cerr << endl;
+
+        /* 3c, Pass 3: Further thinning */
+        for (size_t i=0; i<sz; i++) {
+            if (retain[i]) {
+                if (ros[i] == 1) {
+                    if (retain[(i + sz - 1) % sz] || retain[(i + 1)%sz]) {
+                        if (sig[i] < sig[(i + sz - 1)%sz] || sig[i] < sig[(i + 1)%sz]) {
+                            retain[i] = false;
+                        }
+                    }
+                }
+            }
+        }
+
+        cerr << "pass 3: ";
+        for (size_t i=0; i<sz; i++) {
+            cerr << (retain[i] ? "#" : ".");
+        }
+        cerr << endl;
+
+        Polygon_i new_poly;
+        for (size_t i=0; i<sz; i++) {
+            if (retain[i]) {
+                new_poly.push_back(poly[i]);
+            }
+        }
+        cb(new_poly, cpol);
+    };
+}
+
-- 
cgit