1 files changed, 105 insertions, 0 deletions
diff --git a/src/live_effects/lpe-ellipse_5pts.cpp b/src/live_effects/lpe-ellipse_5pts.cpp
new file mode 100644
index 0000000..e4c9e6f
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+++ b/src/live_effects/lpe-ellipse_5pts.cpp
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/** \file
+ * LPE "Ellipse through 5 points" implementation
+ */
+/*
+ * Authors:
+ *   Theodore Janeczko
+ *
+ * Copyright (C) Theodore Janeczko 2012 <flutterguy317@gmail.com>
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include <2geom/ellipse.h>
+#include <2geom/path-sink.h>
+#include <glibmm/i18n.h>
+
+#include "desktop.h"
+#include "inkscape.h"
+#include "message-stack.h"
+
+#include "live_effects/lpe-ellipse_5pts.h"
+
+namespace Inkscape::LivePathEffect {
+
+LPEEllipse5Pts::LPEEllipse5Pts(LivePathEffectObject *lpeobject)
+    : Effect(lpeobject)
+    , _unit_circle{ // Run an IIFE to build the unit circle.
+        []() {
+            Geom::PathBuilder builder;
+            builder.moveTo({1, 0});
+            builder.arcTo(1, 1, 0, true, true, {-1, 0});
+            builder.arcTo(1, 1, 0, true, true, { 1, 0});
+            builder.closePath();
+            return builder.peek();
+        }()}
+{}
+
+/** Flash a warning message on the status bar. */
+void LPEEllipse5Pts::_flashWarning(char const *message)
+{
+    auto &app = Inkscape::Application::instance();
+    if (auto desktop = app.active_desktop()) {
+        _clearWarning();
+        _error = desktop->messageStack()->flash(Inkscape::WARNING_MESSAGE, message);
+    }
+}
+
+/** Clear our warning from the status bar. */
+void LPEEllipse5Pts::_clearWarning()
+{
+    if (_error == INVALID) {
+        return;
+    }
+    auto &app = Inkscape::Application::instance();
+    if (auto desktop = app.active_desktop()) {
+        desktop->messageStack()->cancel(_error);
+        _error = INVALID;
+    }
+}
+
+/** Fit an ellipse to the first 5 nodes in the given PathVector. */
+Geom::PathVector LPEEllipse5Pts::doEffect_path(Geom::PathVector const &path_in)
+{
+    auto const &source = path_in[0];
+    if (source.size() < 4 /* For 5 nodes, we need at least 4 segments. */) {
+        _flashWarning(_("Five points required for constructing an ellipse"));
+        return path_in;
+    }
+
+    std::vector<Geom::Point> source_points;
+    source_points.reserve(5);
+    for (int i = 0; i < 5; i++) {
+        source_points.push_back(source.pointAt((Geom::Coord)i));
+    }
+
+    Geom::Ellipse ellipse;
+    bool fitting_fail = false;
+    try {
+        ellipse.fit(source_points);
+    } catch (Geom::RangeError &e) {
+        fitting_fail = true;
+    }
+    if (fitting_fail || ellipse.ray(Geom::X) == 0 || ellipse.ray(Geom::Y) == 0) {
+        _flashWarning(_("No unique ellipse passing through these points"));
+        return path_in;
+    }
+    _clearWarning();
+
+    // Transform the unit circle contour to the fitted ellipse.
+    return _unit_circle * ellipse.unitCircleTransform();
+}
+
+} //namespace Inkscape::LivePathEffect
+
+/*
+  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 :