svg-flatten: Add cubic bezier support for newer usvg versions

2 files changed, 120 insertions, 3 deletions

diff --git a/svg-flatten/src/flatten.cpp b/svg-flatten/src/flatten.cpp
index cb7f427..81a240e 100644
--- a/svg-flatten/src/flatten.cpp
+++ b/svg-flatten/src/flatten.cpp
@@ -19,7 +19,107 @@ static inline double calc_sq_distance(double x1, double y1, double x2, double y2
     return dx * dx + dy * dy;
 }
 
-void curve4_div::run(double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4) {
+/* Quadratic beziers */
+
+void curve3_div::run(double x1, double y1, double x2, double y2, double x3, double y3)
+{
+    m_points.clear();
+    m_points.emplace_back(d2p{x1, y1});
+    recursive_bezier(x1, y1, x2, y2, x3, y3, 0);
+    m_points.emplace_back(d2p{x3, y3});
+}
+
+void curve3_div::recursive_bezier(double x1, double y1, double x2, double y2, double x3, double y3, unsigned level)
+{
+    if(level > curve_recursion_limit) 
+    {
+        return;
+    }
+
+    // Calculate all the mid-points of the line segments
+    //----------------------
+    double x12   = (x1 + x2) / 2;                
+    double y12   = (y1 + y2) / 2;
+    double x23   = (x2 + x3) / 2;
+    double y23   = (y2 + y3) / 2;
+    double x123  = (x12 + x23) / 2;
+    double y123  = (y12 + y23) / 2;
+
+    double dx = x3-x1;
+    double dy = y3-y1;
+    double d = fabs(((x2 - x3) * dy - (y2 - y3) * dx));
+    double da;
+    double pi = M_PI;
+
+    if(d > curve_collinearity_epsilon)
+    { 
+        // Regular case
+        //-----------------
+        if(d * d <= m_distance_tolerance_square * (dx*dx + dy*dy))
+        {
+            // If the curvature doesn't exceed the distance_tolerance value
+            // we tend to finish subdivisions.
+            //----------------------
+            if(m_angle_tolerance < curve_angle_tolerance_epsilon)
+            {
+                m_points.emplace_back(d2p{x123, y123});
+                return;
+            }
+
+            // Angle & Cusp Condition
+            //----------------------
+            da = fabs(atan2(y3 - y2, x3 - x2) - atan2(y2 - y1, x2 - x1));
+            if(da >= pi) da = 2*pi - da;
+
+            if(da < m_angle_tolerance)
+            {
+                // Finally we can stop the recursion
+                //----------------------
+                m_points.emplace_back(d2p{x123, y123});
+                return;                 
+            }
+        }
+    }
+    else
+    {
+        // Collinear case
+        //------------------
+        da = dx*dx + dy*dy;
+        if(da == 0)
+        {
+            d = calc_sq_distance(x1, y1, x2, y2);
+        }
+        else
+        {
+            d = ((x2 - x1)*dx + (y2 - y1)*dy) / da;
+            if(d > 0 && d < 1)
+            {
+                // Simple collinear case, 1---2---3
+                // We can leave just two endpoints
+                return;
+            }
+            if(d <= 0) d = calc_sq_distance(x2, y2, x1, y1);
+            else if(d >= 1) d = calc_sq_distance(x2, y2, x3, y3);
+            else            d = calc_sq_distance(x2, y2, x1 + d*dx, y1 + d*dy);
+        }
+        if(d < m_distance_tolerance_square)
+        {
+            m_points.emplace_back(d2p{x2, y2});
+            return;
+        }
+    }
+
+    // Continue subdivision
+    //----------------------
+    recursive_bezier(x1, y1, x12, y12, x123, y123, level + 1); 
+    recursive_bezier(x123, y123, x23, y23, x3, y3, level + 1); 
+}
+
+
+/* Cubic beziers */
+
+void curve4_div::run(double x1, double y1, double x2, double y2, double x3, double y3, double x4, double y4)
+{
     m_points.clear();
     m_points.emplace_back(d2p{x1, y1});
     recursive_bezier(x1, y1, x2, y2, x3, y3, x4, y4, 0);
diff --git a/svg-flatten/src/svg_path.cpp b/svg-flatten/src/svg_path.cpp
index 70d346d..b592ab0 100644
--- a/svg-flatten/src/svg_path.cpp
+++ b/svg-flatten/src/svg_path.cpp
@@ -77,8 +77,7 @@ static pair<bool, bool> flatten_path(ClipperLib::Paths &stroke_open, ClipperLib:
                     (ClipperLib::cInt)round(a[1]*clipper_scale)
             });
 
-        } else { /* Curve to */
-            assert(cmd == "C"); /* guaranteed by usvg */
+        } else if (cmd == "C") { /* Curve to */
             in >> b[0] >> b[1]; /* first control point */
             in >> c[0] >> c[1]; /* second control point */
             in >> d[0] >> d[1]; /* end point */
@@ -95,6 +94,24 @@ static pair<bool, bool> flatten_path(ClipperLib::Paths &stroke_open, ClipperLib:
             }
 
             a = d; /* set last point to curve end point */
+
+        } else { /* Curve to */
+            assert(cmd == "Q"); /* guaranteed by usvg */
+            in >> b[0] >> b[1]; /* control point */
+            in >> c[0] >> c[1]; /* end point */
+            assert (!in.fail()); /* guaranteed by usvg */
+
+            gerbolyze::curve3_div c3div(distance_tolerance_px);
+            c3div.run(a[0], a[1], b[0], b[1], c[0], c[1]);
+
+            for (auto &pt : c3div.points()) {
+                in_poly.emplace_back(ClipperLib::IntPoint{
+                        (ClipperLib::cInt)round(pt[0]*clipper_scale),
+                        (ClipperLib::cInt)round(pt[1]*clipper_scale)
+                });
+            }
+
+            a = c; /* set last point to curve end point */
         }
 
         first = false;