1 files changed, 90 insertions, 0 deletions
diff --git a/src/live_effects/lpe-circle_3pts.cpp b/src/live_effects/lpe-circle_3pts.cpp
new file mode 100644
index 0000000..7982abd
--- /dev/null
+++ b/src/live_effects/lpe-circle_3pts.cpp
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/** \file
+ * LPE "Circle through 3 points" implementation
+ */
+
+/*
+ * Authors:
+ *   Maximilian Albert
+ *
+ * Copyright (C) Johan Engelen 2007 <j.b.c.engelen@utwente.nl>
+ * Copyright (C) Maximilian Albert 2008 <maximilian.albert@gmail.com>
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include "live_effects/lpe-circle_3pts.h"
+
+// You might need to include other 2geom files. You can add them here:
+#include <2geom/circle.h>
+#include <2geom/path-sink.h>
+// TODO due to internal breakage in glibmm headers, this must be last:
+#include <glibmm/i18n.h>
+
+namespace Inkscape {
+namespace LivePathEffect {
+
+LPECircle3Pts::LPECircle3Pts(LivePathEffectObject *lpeobject) :
+    Effect(lpeobject)
+{
+}
+
+LPECircle3Pts::~LPECircle3Pts()
+= default;
+
+static void _circle3(Geom::Point const &A, Geom::Point const &B, Geom::Point const &C, Geom::PathVector &path_out) {
+    using namespace Geom;
+
+    Point D = (A + B)/2;
+    Point E = (B + C)/2;
+
+    Point v = (B - A).ccw();
+    Point w = (C - B).ccw();
+
+    double det = -v[0] * w[1] + v[1] * w[0];
+
+    Point M;
+    if (!v.isZero()) {
+        Point F = E - D;
+        double lambda = det == 0 ? 0 : (-w[1] * F[0] + w[0] * F[1]) / det;
+        M = D + v * lambda;
+    } else {
+        M = E;
+    }
+
+    double radius = L2(M - A);
+
+    Geom::Circle c(M, radius);
+    path_out = Geom::Path(c);
+}
+
+Geom::PathVector
+LPECircle3Pts::doEffect_path (Geom::PathVector const & path_in)
+{
+    Geom::PathVector path_out = Geom::PathVector();
+
+    // we assume that the path has >= 3 nodes
+    Geom::Point A = path_in[0].initialPoint();
+    Geom::Point B = path_in[0].pointAt(1);
+    Geom::Point C = path_in[0].pointAt(2);
+
+    _circle3(A, B, C, path_out);
+
+    return path_out;
+}
+
+/* ######################## */
+
+} //namespace LivePathEffect
+} /* namespace Inkscape */
+
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4 :